Download Glossary of terms from option chapters

IB Physics Course Companion
Glossary of terms from option chapters
A
absolute magnitude
The absolute magnitude of a star is the apparent magnitude it would have if it were observed from
a distance of 10 pc.
[Option E]
absorbed dose
Absorbed dose is the energy absorbed per unit mass of tissue:
E
D=
m
D is the absorbed dose in Gy,
E is the total energy absorbed by the tissue in J,
m is the mass of tissue in kg.
[Option I]
absorption of electromagnetic (EM) waves
When EM waves enter a medium, they can be transmitted, absorbed, or scattered. The absorption
of EM radiation describes EM radiation whose energy is received by the medium.
[Option G]
accommodation
Accommodation is the name given to the process by which the eye can focus on different objects.
The lens changes shape as a result of changes in tension in the ciliary muscles and the
suspensory ligaments.
[Option A]
acoustic impedance
Acoustic impedance is the product of the density and the speed of sound. Very strong reflections
take place from the boundary between two substances with very different acoustic impedances:
z = pc
z is the acoustic impedance in kg m–2 s–1
p is the density in kg m–3
c is the speed of sound in m s–1.
[Option I]
aerial
An aerial is a device that picks up the electromagnetic signals broadcast in a modulated carrier
wave. It can be as simple as a straight piece of wire or a coil of wire.
[Option F]
amplitude modulation (AM)
Amplitude modulation (AM) is the process by which the amplitude of a signal wave is continually
modified to encode the signal wave.
[Option F]
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IB Physics Course Companion
Glossary of terms from option chapters
analogue vs digital
An analogue signal encodes the information using a range of possible values. A digital signal
encodes the information using only two possible values (1 or 0).
The digital transmission of information as compared to the analogue transmission of information is
not as susceptible to the effects of noise, thus increasing the quality of broadcast information.
[Option F]
analogue-to-digital converter (ADC)
An analogue-to-digital converter (ADC) takes a single inputted analogue signal and converts it into
a parallel digital signal outputted on several digital output lines.
[Option F]
angular magnification
Angular magnification is the ratio of the angle subtended by the object for the unaided eye to the
angle subtended by the object with the use of lenses. The angle subtended by the object for the
unaided eye is often assumed to be its maximum possible value, i.e. when the object is placed at
the near point:
θ
M = i
θo
M is the angular magnification (no units)
θi is the angle subtended by the image in °
θo is the angle subtended by the object in °.
[Option G]
angular magnification of an astronomical telescope
The angular magnification of an astronomical telescope is:
f
M = o
fe
M is the angular magnification (no units),
fo is the focal length of the objective lens in m,
fe is the focal length of the eyepiece lens in m.
[Option G]
angular magnification of a simple magnifying glass
The angular magnification of a simple magnifying glass depends on where the image is formed.
Image formed at near point:
D
M = +1
f
Image formed at infinity:
D
M=
f
M is the angular magnification (no units),
D is the distance to the near point in cm (normally 25 cm),
f is the focal length of the lens in cm.
[Option G]
antiparticle
Every particle has its own antiparticle. This has the same mass as its particle but all the quantum
numbers are opposite. Some particles, for example the photon, are their own antiparticle.
[Option J]
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IB Physics Course Companion
Glossary of terms from option chapters
apparent brightness
The apparent brightness of a star is the power per unit area received by an observer on the Earth
in W m–2. The link between brightness and luminosity is:
L
b=
4πd 2
b is the apparent brightness in W m-2
L is the luminosity in W
d is the distance between the star and Earth in m
[Option E]
apparent magnitude scale
The brightness of stars is compared using the (apparent) magnitude scale. This is a logarithmic
scale with a magnitude 1 (the brightest stars in the night sky) star being 100 times brighter than a
magnitude 6 (just visible to the naked eye) star. One ‘step’ on the magnitude scale is equivalent to
a brightness ratio of 2.51 between stars.
[Option E]
apparent vs absolute magnitude
The relationship linking apparent and absolute magnitude is:
⎛d ⎞
m – M = 5 log⎜⎜ ⎟⎟
⎝ 10 ⎠
m is the apparent magnitude (no units),
m is the absolute magnitude (no units),
log is the logarithm to the base 10,
d is the distance from the Earth to the star in pc.
[Option E]
A-scan
An ultrasonic A-scan is an amplitude-modulated scan where the information is presented as a
graph of signal strength against time.
[Option I]
asteroid belt
The asteroid belt in the Solar System is between Mars and Jupiter. It contains many asteroids –
small rocky bodies orbiting the Sun.
[Option E]
astronomical telescope
An astronomical telescope consists of two lenses. The first lens (the objective lens) forms a real,
diminished image of the object being viewed. The second lens (the eyepiece lens) uses this
intermediate image as its object and forms a virtual magnified image. In normal adjustment this
final image is located at infinity.
[Option G]
asymptotic freedom
Asymptotic freedom is a description of how individual quarks and gluons behave while confined
within hadrons – effectively they are free particles within the bounds of their confinement.
[Option J]
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IB Physics Course Companion
Glossary of terms from option chapters
attenuation
Attenuation is the reduction of intensity of a signal as a result of some of the signal energy being
scattered, or absorbed, as it travels along a fibre optic. The defining equation is:
I
attenuation = 10 log 1
I2
attenuation is measured in decibels (dB),
log is the logarithm to the base 10,
I1 is the intensity of the output power in W,
I2 is the intensity of the input power in W.
The attenuation of an optic fibre cable is often expressed in terms of the attenuation per unit length
measured in dB m–1.
[Option F]
attenuation coefficient for X-rays
A parallel beam of X-rays is reduced in intensity as a result of passing through matter as given by:
I = I 0 e – μx
I is the intensity of the transmitted sound in W m–2,
I0 is the original intensity of the sound in W m–2,
e is the number 2.718,
µ is the attenuation coefficient in m-1,
x is the thickness of the material in m.
[Option I]
audio-frequency (AF) amplifier
An audio-frequency (AF) amplifier is an amplifier capable of increasing the amplitude of signals
that are oscillating at audio frequencies (30 Hz to 30 kHz).
[Option F]
average kinetic energy (KE) vs absolute temperature
The relationship between average kinetic energy of particles and the absolute temperature is:
Ek = 32 kT
Ek is average kinetic energy of a system of particles in J,
k is Boltzmann’s constant (1.38 × 10–23 J K–1),
T is the absolute temperature of the system in K.
[Option J]
B
balanced risk
The medical use of radioisotopes exposes a patient to ionizing radiation and therefore involves an
extra risk. There will also be a risk to the patient if radioisotopes are not used and the condition is
either undiagnosed or untreated. Balanced risk is the concept that these two factors need to be
considered when deciding upon what procedures to use.
[Option I]
bandwidth
The bandwidth is the range of frequencies occupied by modulated carrier wave.
[Option F]
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IB Physics Course Companion
Glossary of terms from option chapters
baryons
Baryons are hadrons containing three quarks. Protons and neutrons are baryons.
[Option J]
baryon number
All baryons have a baryon number of +1. All antibaryons have a baryon number of –1. All other
particles have a baryon number of 0. Baryon number is conserved in all reactions.
[Option J]
Big Bang
The Big Bang is the creation of the Universe – mass, space, and time. Approximately 15 billion
years ago, all of the observable matter of the universe was crushed together at a very high density
and temperature. Since then, the universe has been expanding, and thus the temperature and the
density have both been decreasing.
[Option E]
binary stars
Often what appears to be a single star is, in fact, a binary star – two stars in orbit around their
common centre of mass.[Option E]
biological half-life
The biological half-life of a chemical is the time taken for the number of molecules of a chemical in
the body to halve, as a result of biological processes.
[Option I]
bit-rate
A greater number of bits used for each sample allows for a greater quality of transmitted signal.
Thus an increase in bit-rate (the speed at which bits need to be transmitted) will improve the quality
of the reproduction of a transmitted signal.
[Option F]
black holes
Black holes are regions of space-time with extreme curvatures due to the presence of a mass. A
large-mass star ends its red giant phase in a supernova. The remnant in the centre could be a
black hole if its mass is large enough.
[Options E & H]
blooming
Blooming is a thin coating that is added to lenses, solar panels, or solar cells to increase the
amount of light entering the device. The width of the coating is such that, for typical wavelengths,
destructive interference takes place between rays that are reflected from the top and bottom
surfaces of the blooming. This maximizes the amount of light energy that is transmitted.
[Option G]
blueshift
Light from distant stars and galaxies that are coming towards the Earth will show a Doppler shift
towards the shorter wavelengths. This is known as blueshift.
[Option E]
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IB Physics Course Companion
Glossary of terms from option chapters
Bragg scattering equation
The Bragg scattering equation is:
2d sinθ = nλ
d is the distance between the atomic planes in m,
θ is half the angle of deviation by the beam in °,
λ is the wavelength of light in m,
n is an integer (1, 2, 3 etc.).
[Option G]
bremsstrahlung (braking) radiation
Bremsstrahlung (braking) radiation is radiation emitted when a charged particle accelerates. In
particle accelerators this represents energy being lost by the particle which needs to be continually
replaced.
[Option J]
B-scan
An ultrasonic B-scan is a brightness-modulated scan where the information is presented as the
brightness of a dot of light on a screen.
[Option I]
bubble chamber
A bubble chamber is a particle detector that arranges for liquid hydrogen to be superheated as a
result of a sudden expansion. Bubbles of hydrogen are formed within the body of the liquid. Any
ionizing particle passing through the chamber will cause a trail of bubbles, as the bubbles will
preferentially form on the ions. A photograph thus reveals the particle’s path as a track of bubbles.
[Option J]
C
carrier wave
Carrier wave is the name given to the electromagnetic wave that is being modified to transmit a
signal from source to receiver, for example a particular radio frequency.
[Option F]
cellular exchange
The cellular exchange is connected to all of the base stations in a given area. It selects and
monitors the base stations and arranges the allocations of frequency channels to individual base
stations and mobile phones.
[Option F]
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IB Physics Course Companion
Glossary of terms from option chapters
Cepheids
Cepheid variable stars are a particular type of unstable star that have an observed regular variation
in brightness, as a result of a periodic expansion and contraction in their outer layers. There is a
mathematical link between the period of brightness variation and their average luminosity: the
greater the period of the variation, the greater the luminosity. This relationship allows astronomers
to calculate the distance to some galaxies that contain Cepheid variable stars.
[Option E]
Chandrasekhar limit
The Chandrasekhar limit is the maximum size for a white dwarf star to be able to exist
(approximately 1.4 solar masses). Below this mass, electron degeneracy pressure allows the white
dwarf to be stable. Above this mass, further gravitational collapse must take place.
[Option E]
channels of communication
A channel of communication is another phrase for method of transferring information. These
include wire pairs, coaxial cables, optic fibres, radio waves, and satellite communication.
[Option F]
characteristic X-ray spectrum
An X-ray spectrum often contains high intensities of some wavelengths that are specific to the
target’s element. These X-rays are produced as the incoming electrons collide with the target
atoms and cause inner orbital electrons of the target atom to be promoted up to higher energy
levels. As these promoted electrons fall back down, they emit X-rays of a particular wavelength.
[Option G]
chromatic aberration
Chromatic aberration is the term used to describe the fact that rays of different colours will be
brought to a slightly different focus point by the same lens. In general a white point object will focus
into a blurred image of different colours.
[Option G]
clock
A clock pulse (a square-wave signal generated by an oscillator) is used to control and coordinate
all the different processes in digital system.
[Option F]
closed universe
A closed universe is one whose expansion is brought to a stop as a result of the force of gravity.
The universe will then collapse back on itself. This would happen if the density of the universe
were high.
[Option E]
coagulator
A coagulator ensures that blood in a small region will clot, thus potentially stopping bleeding. A
defocused laser acts as a coagulator.
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
coaxial cables
A coaxial cable is formed from two wires arranged in such a way as to reduce electrical
interference. A central wire is surrounded by the second wire in the form of an outer cylindrical
copper tube or mesh. An insulator separates the two wires.
[Option F]
cochlear fluid function
Overall the ear converts sound pressure variations in air into larger pressure variations in the
cochlear fluid. This is achieved as a result of the mechanical advantage of the levers and pistons of
the ossicles, as well as the area of the oval window being much smaller than that of the area of the
eardrum.
[Option H]
coherent
Two sources of light are said to be coherent if there is a constant phase relationship between the
sources. Laser light is coherent because each photon is in phase with all the other photons that are
emitted.
[Option G]
colour of quarks and gluons
Quarks can be one of three different colours (red, green, blue) and antiquarks one of three different
anticolours (antired, antigreen, antiblue). Gluons also carry colour, and their emission and
absorption changes the colours of the individual quarks. Only white or colourless combinations of
quarks are possible, and thus baryons contain three quarks (red, green, and blue = white),
antibaryons contain three antiquarks (antired, antigreen, and antiblue = white) and mesons contain
two quarks (red and antired = colourless, etc).
[Option J]
comets
Comets are mixtures of rock and ice in very elliptical orbits around the Sun.
[Option E]
comparator
The output of a comparator circuit depends on how the input to the circuit compares with a fixed
known value.
[Option F]
compound microscope
A compound microscope consists of two lenses. The first lens (the objective lens) forms a real,
magnified image of the object being viewed. The second lens (the eyepiece lens) uses this
intermediate image as its object and forms a virtual magnified image. In normal adjustment this
final image is located at the near point of the eye.
[Option G]
computed tomography (CT)
Computed tomography (CT) uses a computer to reconstruct a three-dimensional ‘map’ inside the
body in terms of X-ray attenuation. The information comes from a series of scans where the X-ray
source and the detectors are rotated around a patient.
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
cones
Cones are light-sensitive cells responsible for photopic vision (the colour vision that takes place at
normal light levels). There are three different types of cones are mainly located in the centre of the
retina.
[Option A]
constellation
A constellation is a group of stars that, to an observer on the Earth, are in close angular proximity
to one another for a region of the sky with a specific pattern of stars.
[Option E]
continuous X-ray spectrum
An X-ray spectrum contains a range of wavelengths above a minimum wavelength. These X-rays
are produced as the incoming electrons collide with the target atoms and are decelerated. The
energy of the X-ray photon depends on the energy lost by the electron in the collision.
[Option G]
Coolidge tube (intensity)
A Coolidge X-ray tube produces X-rays that result from the collisions between fast-moving
electrons and a metal target. The electrons are emitted from a heated cathode (thermionic
emission) and are accelerated towards the target by a p.d. The target is cooled. The intensity of
the X-rays is increased by increasing the heater current to the cathode.
[Option G]
cosmic microwave background radiation
Cosmic microwave background radiation is the microwave radiation that is coming towards us from
all directions in space and provides evidence for the existence of the Big Bang. The spectrum of
this radiation is in agreement with black-body radiation for an object at a temperature of 2.7 K.
Radiation released soon after the Big Bang would change wavelength as the universe expanded
and is consistent with the current average temperature of the universe.
[Option E]
critical angle
When a ray crosses the boundary between two media, for example from a more optically dense
medium into a less optically dense medium, it is refracted away from the normal. The critical angle
is the angle of incidence in the denser medium (i.e. between the ray and the normal) that produces
a refracted ray that has grazing emergence along the boundary (i.e. has a refracted angle of 90°).
[Option F]
critical density
The critical density is the density of the universe that would create a flat universe. It is
approximately 5 × 10–26 kg m–3.
[Option E]
cyclotron
A cyclotron accelerates charged particles as they travel in an outward spiral inside two hollow
electrodes in a vacuum. Circular motion is achieved with a fixed magnetic field, and acceleration is
achieved as the charged particles cross the gap between two hollow electrodes. An alternating p.d.
between the electrodes ensures that the particles always accelerate in the gap.
[Option J]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
D
dark matter
Dark matter makes up the majority of the mass in the universe and its nature is unknown. It is
called dark matter because it does not emit light. The mathematics of orbital motion allow us to
calculate how much matter must be contained within a galaxy in order for the outer stars to remain
in orbit. The stars and their associated planes account for a maximum of 10% of the matter that
must be there. The unexplained 90% is dark matter.
[Option E]
de Broglie relationship
De Broglie hypothesized that all moving particles have a ‘matter wave’ associated with them. de
Broglie equation is:
h
p=
λ
p is the momentum in kg m s-1
h is Planck’s constant (6.63 × 10–34J s)
λ is the wavelength in m.
The same equation can be used to calculate the momentum associated with photons.
[Option J]
deep inelastic scattering
Deep inelastic scattering experiments involve scattering leptons off hadrons when large amounts of
energy (compared to their rest masses) and momentum are transferred to the hadrons. Charged
constituents of the hadrons (i.e. quarks) can be identified.
[Option J]
demodulator
A demodulator is a circuit that reconstructs the signal wave from a modulated carrier wave.
[Option F]
depth of vision
The depth of vision is the range of distances that are in focus at any given instant. Normal vision
has the eye focused on infinity (when the eye is relaxed) and this results in the greatest depth of
vision.
[Option A]
diagnostic applications
Diagnostic applications are medical procedures designed to find out what is wrong with a patient.
[Option I]
diagnostic frequency, factors affecting
The diagnostic frequency chosen for ultrasound is a balance between resolution and attenuation.
To resolve small objects, a small wavelength is needed, but small-wavelength ultrasound is
strongly attenuated.
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
diffraction grating
A diffraction grating is a series of parallel slits with a regular separation. Increasing the total
number of slits does not affect the separation of the bright fringes but it does make them sharper
and brighter.
[Option G]
diffraction grating formula
The diffraction grating formula is:
d sinθ = nλ
d is the separation between the slits in m,
λ is the wavelength of light in m,
θ is the angle between the straight through direction and the bright fringe under consideration in °,
n is an integer (1, 2, 3 etc.).
[Option G]
digital-to-analogue converter (DAC)
A digital-to-analogue converter (DAC) takes a parallel digital signal inputted on several digital lines
and converts it into a single outputted analogue signal.
[Option F]
dioptre
The dioptre (dpt) is the unit for the power of a lens:
1 dpt = 1 m–1
[Option G]
discomfort in normal hearing
The approximate magnitude of intensity level at which discomfort is experienced by a person with
normal hearing is 120 dB.
[Option I]
dispersion
Dispersion is the phenomenon by which white light entering a prism is split into its component
colours, as a result of the different refraction indexes for different wavelengths.
[Option G]
dose equivalent and quality factor (relative biological effectiveness)
Dose equivalent is a measure of the radiation damage that occurs in tissues. It is defined as:
H = QD
H is the dose equivalent in Sv,
Q is the quality factor or relative biological effectiveness for different radiations (see table below) –
no unit,
D is the absorbed dose in gy.
Radiation Q
X-rays
1
γ-rays
1
β-particles 1
α-particles 20
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
double-slit experiment
The double-slit experiment for light involves two coherent sources of monochromatic light which
are often narrow slits in an otherwise dark obstacle. The light from these two sources interferes
and produces light and dark fringes.
[Option G]
double-slit fringe separation
There are several equivalent equations for the analysis of the double-slit fringe pattern:
λD
s=
d
nλ
sinθ =
d
For a bright fringe:
x nλ
=
D d
For a dark fringe:
x ⎛
1⎞ λ
= ⎜n + ⎟
D ⎝
2⎠d
s is the fringe separation in m,
λ is the wavelength of light in m,
D is the distance from slits to screen in m,
d is the separation between the slits in m,
θ is the angle between the straight-through direction and the bright fringe under consideration in °,
n is an integer (1, 2, 3 etc.),
x is the distance on the screen from the central maximum to the fringe under consideration in m.
[Option G]
down-link frequency
Different frequencies are used for sending information to and from a satellite. The down-link
frequency is the frequency used for receiving information from a satellite.
[Option F]
E
ear, human, basic structure of
Longitudinal sound vibrations enter the outer ear and arrive at the ear drum (tympanic membrane).
In the middle ear, three small bones (the malleus, incus, and stapes), which are collectively known
as the ossicles, pass the oscillations into the fluid in the inner ear via the oval window. Oscillations
in the fluid are converted in the cochlea into electrical signals that are sent along the auditory nerve
to the brain. Another part of the inner ear not involved in hearing sounds is the semicircular canals,
which are involved in detecting movement and keeping the body balanced.
[Option H]
ear, response of
There is a logarithmic response of the ear to intensity.
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
eclipsing binary stars
A spectroscopic binary is a pair of stars whose existence can be deduced from analysis of
variations in the brightness of the light received. Over time the wavelengths show a periodic ‘dip’ in
brightness.
[Option E]
effective half-life
The effective half-life of a radioactive isotope in the body is the time taken for the number of atoms
of the radioactive isotope in the body to halve, as a result of both biological processes and
radioactive decay.
[Option I]
Einstein’s mass–energy equivalence formula
The formula representing the equivalence of mass and energy is:
E0 = m0 c 2
E0 is the rest energy of a mass in J,
m0 is the rest mass in kg,
c is the velocity of light in m s–1 (3 × 108 m s–1).
[Option H]
Einstein’s principle of equivalence
The principle of equivalence is that there is no difference between an accelerating frame of
reference and a gravitational field; for example, inside a closed elevator it would be impossible to
distinguish between an upward acceleration of the elevator and a downward gravitational field.
[Option H]
electromagnetic (EM) waves
Electromagnetic (EM) waves are changing electric and magnetic fields that propagate through
space at a given speed in a vacuum: the speed of light. They are produced by oscillating electric
charges. EM waves are transverse waves – the plane of the oscillating electric field is at 90° to the
plane of the oscillating magnetic field.
[Option G]
electron degeneracy pressure
The quantum mechanical process that allows white dwarf stars to be stable and avoid further
gravitational collapse.
[Option E]
elementary (fundamental) particles
An elementary particle is one with no internal structure, for example quarks, leptons, and exchange
particles.
[Option J]
elementary (fundamental) particles in the early universe
At the very high temperatures of the early universe, only elementary (fundamental) particles could
exist. Over time, expansion gave rise to cooling, eventually resulting in temperatures at which light
nuclei could be stable, followed by temperatures at which atoms could be formed.
[Option E]
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IB Physics Course Companion
Glossary of terms from option chapters
endoscopes
An endoscope consists of a tube containing a collection of optical fibres. This tube can be inserted
inside the body without the need for surgery, and illumination from an outside source can be
directed onto a region under investigation. Reflected light is collected and further optical fibres are
used to allow an image to be viewed.
[Option I]
energy considerations in particle production
The energy equation that links the centre-of-mass frame with the laboratory frame for the collision
between a moving particle and a stationary particle is:
2
2
2
E a = 2Mc 2E + (Mc 2 ) + (mc 2 )
Ea is the energy available for the formation of particles as a result of a collision in MeV (centre-ofmass frame),
M is the rest mass of the target particle in MeV c–2,
c is the speed of light (substituted as symbol),
E is the total energy of the incoming particle in the laboratory frame (i.e. rest energy + kinetic
energy) in MeV,
m is the rest mass of the incoming particle in MeV c–2.
[Option J]
enhancement in X-ray detection
Enhancement in X-ray detection is any process that intensifies the image produced, for example
intensifying screens or image-intensifier tubes.
[Option I]
equilibrium of a star
A star’s size is stable because it is in equilibrium between radiation ‘pressure’ (the tendency of the
hot central mass to expand outwards into the surrounding vacuum of space) and gravitational
‘pressure’, the inward pull of gravity.
[Option E]
exchange particles
Exchange particles mediate the known interactions in nature. They are:
EM
photons
weak
W+, W–, Z0
strong
8 gluons
gravity
gravitons
[Option J]
exposure
The exposure is the total amount of ionization produced as a result of ionizing radiation. It is
defined as:
Q
X=
m
X is the exposure in C kg–1,
Q is the total charge of one sign produced as the radiation passes through air in C,
m is the mass of air in kg.
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
eye, human, basic structure of
Looking into somebody’s eyes, the iris (the coloured part) has a dark central gap (the pupil) that
changes in size to control the amount of light that enters the eye. Light entering the eye passes
through the cornea (where it is refracted) and then the aqueous humour before passing through
the pupil and going through the lens. Further refraction takes place at the lens, whose shape is
controlled by the ciliary muscles and the suspensory ligaments. The light then passes through the
vitreous humour before striking the retina where light-sensitive cells (rods and cones) respond to
the light by sending electrical signals via the optic nerve to the brain. A part of the retina is
occupied by the optic nerve, resulting in a blind spot that is not sensitive to light.
[Option A]
eyepiece lens
The second lens in an optical instrument involving two lenses. Light from the object being viewed
leaves the instrument and enters the observer’s eye via the eyepiece lens.
[Option G]
F
far point
The far point is the furthest point that can be focused upon without straining or optical aids. In
normal vision, the distance to the near point is taken as infinite.
[Options A & G]
Feynman diagram
Feynman diagrams are space-time diagrams used to represent possible particle interactions and
calculate the overall probability of an interaction taking place.
[Option J]
film badge
A film badge is a piece of photographic film held within a plastic container and not exposed to light.
It is used to monitor the exposure received by those who work with radiation. Different filters are
placed either side of the film so as to be able to determine the nature of the ionizing radiation that
has affected the film.
[Option I]
flat universe
A flat universe is one that continues to expand forever. The force of gravity will continually slow
down the rate of recession of the galaxies. The density of the universe is an exact amount so that it
takes an infinite amount of time to bring the expansion to a halt. This happens if the density of the
universe were equal to the critical density.
[Option E]
focal length
The focal length is the distance between the centre of the lens and the focal point.
[Option G]
focal point
The focal point of a lens is the point on the principal axis, to which rays that were parallel to the
principal axis are brought to focus after passing through the lens.
[Option G]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
frame of reference
Any observer that makes observations of events with respect to where they are with rulers and
clocks that are at rest with respect to the observer is known as a frame of reference.
[Option H]
frequency modulation (FM)
Frequency modulation (FM) is the process by which the frequency of a signal wave is continually
modified to encode the signal wave.
[Option F]
fundamental interactions
The four fundamental interactions of nature are electromagnetic, strong, weak, and gravity. The
electromagnetic and the weak interactions are two aspects of the same interaction, the
electroweak interaction.
[Option J]
fusion
Fusion is main energy source in stars.
[Option E]
G
gain
The gain of an amplifier is defined by:
V
G = OUT
VIN
G is the gain (and has no units: it is a ratio),
VOUT is the output voltage in V,
VIN is the input voltage in V.
[Option F]
gain of a non-inverting amplifier
The gain of non-inverting amplifier is given by:
R
G = 1+ F
R
G is the gain (and has no units: it is a ratio),
RF is the feedback resistor in Ω,
R is the input resistor (the resistor between non-inverting input and 0 V) in Ω.
[Option F]
gain of an inverting amplifier
The gain of an inverting amplifier is given by:
R
G=– F
R
G is the gain (and has no units: it is a ratio),
RF is the feedback resistor in Ω,
R is the input resistor in Ω.
[Option F]
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IB Physics Course Companion
Glossary of terms from option chapters
galactic cluster
A galactic cluster is a number of galaxies (e.g. 103) that are located relatively close to one another.
[Option E]
galactic supercluster
A galactic supercluster is a large number of galactic clusters that are located relatively close to one
another. Typically the galaxies are arranged together in bands.
[Option E]
Galilean transformation
A Galilean transformation is a set of equations that allows for measurements in one frame of
reference to be deduced from another frame of reference by applying classical mechanics (i.e.
without taking the theory of relativity into consideration).
Suppose that, according to an observer in a frame S, the frame of reference S′ is moving past S
with a constant velocity v in the x direction. The frames are on top of one another when t = t′ = 0.
Then:
y′ = y
z′ = z
t′ = t
and
x′ = x – vt
u′= u – v
In frame S:
x, y, and z are measurements of distance in m,
t is the measurement of time in s,
u and v are measurements of velocity in m s-1,
The corresponding measurements in frame S′ are:
x′, y′ and z′ – the measurements of distance in m,
t' – the measurement of time in s,
u′ – the measurement of velocity in m s-1.
[Option H]
geostationary satellite
A geostationary satellite maintains the same position relative to a point on the Earth’s surface. The
orbit is above the equator with time period of exactly 24-hours.
[Option F]
geostationary satellites, frequencies used by
The frequencies used by a geostationary satellite for communications are all in the super-highfrequency (SHF) range, i.e. GHz.
[Option F]
gravitational attraction by warping of space-time
The gravitational attraction between two objects can be expressed in terms of the warping
(bending) of space-time by the presence of any mass.
[Option H]
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IB Physics Course Companion
Glossary of terms from option chapters
gravitational lensing
Gravitational lensing is the bending of light around massive galaxies giving the same results as
light is bent by a convex lens.
[Option H]
gravitational mass
Gravitational mass is the property of an object that determines how much gravitational force it feels
when near another object.
gravitatio nal force ∝ m(g )
gravitational force is measured in N,
m(g) is the gravitational mass in kg.
[Option H]
gravitational red shift
Clocks slow down in a gravitational field. This results in a change of frequency for a photon when it
moves through a gravitational field. If the gravitational field is constant, then the frequency change
can be calculated from:
Δf g Δh
= 2
f
c
Δf is the change in frequency in Hz,
f is the frequency emitted at the source in Hz,
g is the value of the uniform gravitational field in N kg–1,
Δh is the height difference in the gravitational field in m,
c the velocity of the light in m s-1 (3 × 108 m s–1).
[Option H]
H
hadrons
All particles (apart from exchange particles) can be classified as either hadrons (‘heavy’) or leptons
(‘light’). Hadrons can be further classified as either baryons or mesons. All hadrons are composed
of quarks. Protons and neutrons are hadrons.
[Option J]
Hafele–Keating experiment
In the Hafele–Keating experiment, atomic clocks were put into aircraft and flown, both eastwards
and westwards, around the world. Before and after the flights the times on the clocks were
compared with clocks that remained fixed in the same location on the surface of the Earth. The
results of the experiment agreed with the predictions of special relativity within the uncertainties of
the experimental procedure.
[Option H]
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IB Physics Course Companion
Glossary of terms from option chapters
half-lives
Different half-lives are linked with the following formula:
1
1
1
=
+
TE TP TB
TE is the effective half-life of a radioactive isotope in the body measured in s,
TP is the physical half-life of a radioactive isotope measured in s,
TB is the biological half-life of a radioactive isotope in the body measured in s.
[Option I]
half-value thickness
The half-value thickness is the thickness of a material that results in the intensity of X-rays being
reduced to a half of their original value. It is related to the attenuation coefficient as follows:
μx 1 = ln 2
2
μ is the attenuation coefficient in m-1,
x 21 is the half-value thickness of the material in m,
ln is the natural logarithm (logarithms to the base e).
[Option I]
hardness of X-rays
The hardness of an X-ray beam measures its penetration power. High frequencies are harder.
[Option G]
Hertzsprung–Russell diagram (and main-sequence stars)
Hertzsprung–Russell diagrams are plots of data from different stars with each point representing a
different star. Their axes have different possible labels, but whichever one is chosen the diagram
will be equivalent.
The vertical axis is a logarithmic plot of the luminosity or the absolute magnitude of the star.
The horizontal axis is the spectral class of the star or a (decreasing) logarithmic plot of it
temperature. The majority of stars are found on a line that runs from top left to bottom right called
the main sequence.
[Option E]
Higgs particle
The Higgs particle is a hypothesized elementary particle necessary to explain the process by which
particles can acquire mass.
[Option J]
Hubble constant used to estimate the age of the universe
If the speed of recession of the galaxies has been constant since the beginning of the universe,
then:
1
T=
H0
T is the age of the universe in s,
H0 is the Hubble constant in s–1 (note that a conversion is necessary between the ‘usual’ units of
km s–1 Mpc–1 and the units of s–1).
[Option E]
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IB Physics Course Companion
Glossary of terms from option chapters
Hubble’s law
The recession velocity of a galaxy is proportional to the distance of the galaxy from Earth:
v = H 0d
v is the recession speed of the galaxy in km s–1,
d is the distance of the galaxy from Earth in Mpc,
H0 is the Hubble constant in km s–1 Mpc–1.
[Option E]
I
ideal operational amplifier (op-amp)
An ideal operational amplifier (op-amp) has infinite gain and draws zero current on its inputs.
[Option F]
improving contrast of an X-ray image
The contrast of an X-ray image can be improved by introducing a dense substance to increase the
difference in densities involved, for example a barium meal.
[Option I]
improving sharpness of an X-ray image
The sharpness of an X-ray image can be improved by using tomography to make the X-ray image
focus on a certain region or ‘slice’ through the patient. All other regions are blurred out of focus.
[Option I]
inertial frame of reference
An inertial frame is a frame of reference in which the laws of inertia (Newton’s law) apply. An
inertial frame is one that is either stationary or moving with a constant velocity.
[Option H]
inertial mass
Inertial mass is the property of an object that determines how it responds to a given force:
F
Inertial mass m(i) =
a
m(i) is the inertial mass in kg.
[Option H]
intensity level (IL)
Sound intensity level is defined as:
I
IL = 10 log
I0
IL is the intensity level measured in dB,
log is the logarithm to the base 10,
I is the intensity of the received sound in W m–2,
I0 is the minimum audible intensity of sound (1.0 × 10–12 W m–2).
[Option I]
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IB Physics Course Companion
Glossary of terms from option chapters
intensity
The intensity of a sound wave is the power per unit area that is received by the observer:
p
I=
A
I is the intensity in W m–2,
p is the power received in W,
A is the area at right angles to the wave that receives the power.
[Option I]
interference between two sources, conditions for
In order to observe interference between two sources, they must be coherent sources of roughly
the same amplitude.
[Option G]
inverting amplifier circuit using an op-amp
An inverting amplifier circuit has the non-inverting input of the op-amp connected to 0 V. There is
an input resistor between the inverting input of the op-amp and the input signal, and a feedback
resistor connected between the output and the inverting input of the op-amp.
[Option F]
K
kinetic energy of a particle
The kinetic energy of a particle moving at relativistic speeds is given by:
E K = (γ – 1)m0 c 2
EK is the kinetic energy of the moving particle in J,
γ is the Lorentz factor for the moving object (and has no units: it is a number ≥ 1),
m0 is the rest mass of the particle in kg,
c is the velocity of light in m s–1 (3 × 108 m s–1).
[Option H]
L
laser light
Laser stands for Light Amplification by Stimulated Emission of Radiation. Electrons are promoted
to higher energy levels. If a significant population inversion exists, the electrons can be stimulated
by a photon of the correct frequency to fall down and emit further identical photons. This emission
can produce significant light amplification.
[Option G]
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IB Physics Course Companion
Glossary of terms from option chapters
length contraction
The length of an object as measured by a moving frame of reference will be less than the length of
the object as measured in the object’s own frame of reference. This effect is known as length
contraction. The length contraction formula is:
L
L= 0
γ
L is the length of an object in m as measured in the frame in which the object is moving,
L0 is the proper length for the object in m,
γ is the Lorentz factor for the moving frame (and has no units: it is a number ≥ 1).
[Option H]
leptons
Leptons are elementary particles. There are six different types of lepton: electron, electronneutrino, muon, muon-neutrino, tau, tau-neutrino.
[Option J]
lepton number
The total number of leptons in each family is conserved in any reaction.
[Option J]
light clock
A light clock is an imaginary device in which a beam of light bounces between two mirrors. The line
taken by the light between bounces is the basic time interval measured by the clock.
[Option H]
light-year
A unit of distance to measure the distance travelled by light in a vacuum during one year. It is
equal to 9.46 × 1015 m.
[Option E]
linear accelerator
In a linear accelerator, charged particles are accelerated along a horizontal evacuated tube. A
radio-frequency alternating p.d. is connected along a series of hollow electrodes. The charged
particles are accelerated by the electric field between the electrodes.
[Option J]
linear magnification
Linear magnification is the ratio between the size of the image and the size of the object:
h
v
m= i =–
h0
u
m is the linear magnification (no units),
hi is the height of the image in m,
ho is the height of the object in m,
v is the image distance in m,
u is the object distance in m.
[Option G]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
Lorentz factor
The Lorentz factor is:
1
γ=
v2
1– 2
c
γ is the Lorentz factor (and has no units: it is a number ≥ 1),
v is the velocity of the moving object in m s-1,
c is the velocity of the light in m s–1 (3 × 108 m s–1).
[Option H]
loudspeaker
A loudspeaker converts electrical oscillations into sound waves at the same frequency.
[Option F]
LSB and MSB
The least-significant bit (LSB) is the bit representing 20 and is the furthest on the right when a
binary number is written down. The most-significant bit (MSB) is the bit representing the highest
power of 2 and is the furthest on the left when a binary number is written down.
[Option F]
luminosity
The luminosity of a star is the total power radiated in W.
[Option E]
M
MACHOs
Massive astronomical compact halo objects (MACHOs) are one possible theoretical explanation for
dark particles.
[Option E]
malignant
Malignant cells are cancerous cells.
[Option I]
mass of star, effect on the end product of nuclear fusion and changes in nucleosynthesis
Stars on the main sequence are fusing hydrogen nuclei to create helium nuclei. A star’s mass
affects the end product of nuclear fusion. Small-mass stars go through a red giant phase in which
helium is fused, creating carbon and oxygen. This process ends in a planetary nebula with the
remnant being a white dwarf. Larger-mass stars end up as a red supergiant in which the elements
up to iron can be fused. This process ends in a supernova with the remnant being a neutron star or
a black hole.
[Option E]
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IB Physics Course Companion
Glossary of terms from option chapters
mass–luminosity relationship
The luminosity of a star on the main sequence is related to its mass by:
L ∝ mn , where 3 < n < 4
L is the luminosity in W,
m is the mass in kg,
n is a number between 3 and 4.
[Option E]
material dispersion
Material dispersion is a process by which a pulse that starts out as a square wave will tend to
spread out as it travels along an optical fibre, as a result of the different frequencies that make up
the pulse having slightly different speeds along the fibre.
[Option F]
mesons
Mesons are hadrons containing a quark/antiquark pair.
[Option J]
Michelson–Morley interferometer
The Michelson–Morley interferometer involves two beams of light that have paths that are at right
angles to one another. Having travelled the different paths, the light was brought together where it
interfered, producing constructive and destructive interference patterns. It was expected that a
rotation of the apparatus would cause the interference pattern to move, and the speed of the Earth
through the aether could be calculated. The rotation did not produce any observable change in the
interference pattern, which implies that the aether does not exist. The result is consistent with the
postulate of the constancy of the speed of light.
[Option H]
minimum wavelength limit
The minimum wavelength limit of an X-ray spectrum corresponds to a collision where all of the
incoming electron’s energy has been converted into an X-ray photon:
hc
λmin =
eV
λmin is the minimum wavelength of emitted X-rays in m
h is Planck’s constant (6.63 × 10–34J s)
c is the speed of light (3 × 108 m s–1)
e is the charge on an electron (1.6 × 10–19 C)
V is the accelerating potential difference in V.
[Option G]
mobile phone cells
In the mobile phone system, any area is divided into a number of cells (each with its own base
station) to which is allocated a range of frequencies for communications.
[Option F]
modal dispersion
Modal dispersion is a process by which a pulse that starts out as a square wave will tend to spread
out as it travels along an optical fibre, as a result of the different paths possible down an optical
fibre that has a significant core diameter.
[Option F]
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IB Physics Course Companion
Glossary of terms from option chapters
modulation
Modulation is the general term for the way in which a carrier wave is modified in order to transmit a
signal from source to receiver. Two important types are amplitude modulation (AM) and frequency
modulation (FM).
[Option F]
monochromatic
Monochromatic means of a single colour or frequency.
[Option G]
muon decay experiments
Cosmic rays cause muons to be created high up in the atmosphere moving with velocities close to
the speed of light. The observed half-life of these moving muons is much longer than the half-life of
muons created at rest in the laboratory. The measured increase in half-life is in agreement with the
time dilation formula.
[Option H]
N
near point
The near point is the closest point that can be brought into focus by the unaided eye. For normal
vision, the near point is taken to be 25 cm away from the observer.
[Options A and G]
neutral current
Weak interactions involving the neutral Z0 boson are called neutral currents.
[Option J]
neutron degeneracy pressure
The quantum mechanical process that allows neutron stars to be stable and avoid further
gravitational collapse.
[Option E]
neutron star
A large-mass star ends its red giant phase in a supernova. The remnant in the centre could be
visible as a neutron star if its mass is small enough.
[Option E]
Newton’s model of the universe
From observations of the stars, Newton’s model of the universe is that it is infinite, uniform, and
static.
[Option E]
noise
Noise, in any signal, is the term used to describe unwanted additions that degrade the quality of
the signal. Dispersions and scatterings that take place within an optical fibre will mean that the
output signal is not identical to the input signal, but also includes some noise.
[Option F]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
non-inverting amplifier circuit using an op-amp
An inverting amplifier circuit has the inverting input of the op-amp connected to 0 V via an input
resistor. The input signal is connected directly to the non-inverting input of the op-amp and a
feedback resistor connected between the output and the inverting input of the op-amp.
[Option F]
normal hearing
The range of audible frequencies experienced by a person with normal hearing is from 20 Hz to 20
kHz.
[Option I]
nuclear magnetic resonance (NMR) imaging
Nuclear magnetic resonance (NMR) imaging is a very complicated process in which the response
of tissues that are placed in a strong non-uniform magnetic field to a pulse of radio waves is
analysed to produce an image, for example brain scans.
[Option I]
nucleosynthesis
Nucleosynthesis is the process by which nuclei of different elements are formed.
[Option J]
O
objective lens
The first lens in an optical instrument involving two lenses. Light from the object being viewed
enters the instrument via the objective lens.
[Option G]
observed loudness
A change in observed loudness is the response of the ear to a change in intensity of sound.
[Option I]
Olbers’ paradox
Olbers’ paradox is that the night sky is dark, but if one accepts Newton’s model of the universe,
then the night sky should be bright. In simple terms, whatever direction you look in, you should
eventually come across a star.
A more mathematical analysis shows that more distant stars will appear dimmer, but this effect is
cancelled out by the increased likelihood of observing stars at larger distances.
[Option E]
open universe
An open universe is one that continues to expand forever. The force of gravity will slow down the
rate of recession of the galaxies, but it is not strong enough to bring the expansion to a halt. This
would happen if the density of the universe were low.
[Option E]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
Oppenheimer–Volkoff limit
The Oppenheimer–Volkoff limit is the maximum size for a neutron star to be able to exist (between
2 and 3 solar masses). Below this mass, neutron degeneracy pressure allows the neutron star to
be stable. Above this mass, further gravitational collapse must take place into a black hole.
[Option E]
optical fibre transmission, role of amplifiers in
Amplifiers are used to increase signal strength and thus correct for attenuation. An amplifier will
also increase any noise that has been added to the electrical circuit
[Option F]
optical fibre transmission, role of reshapers in
A reshaper can reduce the effects of noise on a digital signal, but returns the signal to a series of
1s and 0s with sharp transitions between the allowed levels.
[Option F]
optical flats
An optical flat is a region that is designed to be completely smooth.
[Option G]
output circuit using light-emitting diodes (LEDs)
Light emitting diodes (LEDs) emit light when current flows through them. If a reverse p.d. is applied
across the LED, no current flows. Most LEDs require a protective resistor in series to limit the
forward current.
[Option F]
P
pair annihilation
Pair annihilation is the name given to the process in which a matter particle and an antimatter
particle interact, and both particles cease to exist.
[Option J]
parallel films, constructive and destructive interference in
The conditions for interference in parallel films are:
Destructive interference:
2nt cos φ = mλ
Destructive interference:
2nt cos φ = m + 21 λ
(
)
n is the refractive index of the medium in the film (no units),
t is the thickness of the film in m,
φ is angle of refraction (the angle between the refracted ray and the normal) in the film in °,
m is an integer (1, 2, 3, etc.),
λ is the wavelength of light in m.
[Option G]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
parallel-to-serial converter
A parallel-to-serial converter converts a parallel digital signal inputted on several digital input lines
into a serial (one-bit-at-a-time) output on a single output digital line.
[Option F]
parsec
The parsec is an astronomical measurement of distance equal to 3.26 light-years. It is the distance
to a star that has a parallax angle of one second of arc, or
o
⎛ 1 ⎞
⎜
⎟
⎝ 3600 ⎠
[Option E]
particle production
The total energy required to created a moving particle is given by:
E = mc 2 + E K
E is the total energy in MeV
m is the rest mass of the particle in MeV c–2
c is the speed of light (substituted as a symbol)
EK is the kinetic energy in MeV.
[Option J]
Pauli exclusion principle
The Pauli exclusion principle states that no two fermions can occupy the same quantum state, i.e.
no two fermions that are in the same quantum system as each other can have exactly the same
set of quantum numbers as each other.
[Option J]
phase change on reflection, conditions for
When light is reflected back from an optically denser medium, there is a phase change of π. When
light is reflected back from an optically less dense medium, there is no phase change.
[Option G]
photomultiplier
Some particles cause a photon to be emitted from certain materials. A photomultiplier allows
individual photons (and thus individual particles) to be detected by using the photon to cause the
photoelectric emission of an electron from a cathode. This single electron is accelerated and
causes further electrons to be emitted in an avalanche of collisions which results in a pulse of
current.
[Option J]
physical half-life
The physical half-life of an isotope is the time taken for the number of nuclei concerned to halve, as
a result of radioactive decay.
[Option I]
piezoelectric crystals
Piezoelectric crystals are quartz crystals that change shape when an electric current flows. They
also generate p.d.s when receiving sound pressure waves, and thus one crystal can be used for
the generation and detection of ultrasound.
[Option I]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
pion decay experiments
A particle known as a neutral pion can decay into two gamma-ray photons. When this decay takes
place with pions moving close to the speed of light, the speed of the gamma-rays was measured to
be equal to the speed of light. This is consistent with the speed of light being independent of the
speed of its source.
[Option H]
planetary nebula
A low-mass star ends its red giant phase by ejecting the other layers of the star. The remains of
the outer layers are visible as a planetary nebula. The remnant in the centre is a white dwarf star.
[Option E]
polar-orbiting satellites
Polar-orbiting satellites are ones that are in a low-altitude orbit that passes over the poles. They
can be used for monitoring the weather, remote sensing, or military surveillance.
[Option F]
population inversion
Normally, electrons will always occupy the lowest available energy levels in an atom. A population
inversion is said to exist when a large number of electrons are at higher energy levels than would
be normally expected. They can be easily stimulated to fall down to the lower energy level.
[Option G]
Pound–Rebka experiment
The Pound–Rebka experiment was able to measure the decrease in frequency of a gamma-ray
photon as it changed height in a gravitational field.
[Option H]
power of a lens
The power of a lens is the reciprocal of the focal length:
1
P=
f
P is the power of the lens in dpt,
f is the focal length of the lens in m.
[Option G]
power spectrum of a carrier wave
A modulated carrier wave will contain different frequencies. A power spectrum is plot of amplitude
(on the y axis) vs frequency (on the x axis).
[Option F]
primary colours
The primary colours are red, green, and blue. By adding combinations of these three frequencies
at different intensities, the other colours of the rainbow can be perceived (red and green light
together appears as yellow light).
[Option A]
principle axis of a lens
The principle axis is the line going directly through the middle of the lens. Technically it joins the
centres of curvatures of the two surfaces.
[Option G]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
proper length
The proper length of an object is the length as measured in a frame of reference where the two
measurement events take place at the same time. It is the length of an object recorded in the
object’s frame of reference.
[Option H]
proper time interval
The proper time interval between two events is the time as measured in a frame of reference
where the two events take place at the same point in space. It is the shortest possible time that any
observer could correctly record for the time interval.
[Option H]
public switched telephone network (PSTN)
The public switched telephone network (PSTN) is the arrangement of phones that are physically
connected with wires (landline). Different users are connected to one another by the exchange
switching connections.
[Option F]
pulsars
Pulsars are cosmic sources of very weak radio wave energy that pulsate at a very rapid and
precise frequency. They have been theoretically linked to rotating neutron stars.
[Option E]
pulse oximetry
Pulse oximetry involves shining red and infrared laser light through a thin part of a patient’s
anatomy. The changing relative amount between two wavelengths can be used to determine the
ratio of blood cells with oxygen to those without oxygen.
[Option I]
Q
quantum numbers
All particles (elementary, as well as composite) are specified in terms of their mass and various
quantum numbers that define the particle concerned. Quantum numbers include electric charge,
spin, strangeness, colour, lepton number, and baryon number.
[Option J]
quark confinement
The term ‘quark confinement’ means that isolated quarks cannot be observed. If sufficient energy
is supplied to a hadron in order to attempt to isolate a quark, then more hadrons (or mesons) will
be produced rather than isolated quarks
[Option J]
quarks
Quarks are the elementary particles that make up all hadrons (baryons and mesons). There are six
different types of quark: up, down, charm, strange, top, and bottom.
[Option J]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
R
radio-frequency (RF) amplifier
A radio-frequency (RF) amplifier is an amplifier capable of increasing the amplitude of a signals
that are oscillating at radio frequencies (104 Hz and above).
[Option F]
range of interactions
The formula for estimating for the range of interactions is:
h
R≈
4πmc
R is the approximate range of the interaction in m,
h is Planck’s constant (6.63 × 10–34J s),
m is the rest mass of the exchange particle in kg,
c is the speed of light (3 × 108 m s–1).
[Option J]
real image
A real image is one in which the rays of light pass through the image. It can be projected onto a
screen.
[Option G]
‘real-is-positive’ convention
The ‘real-is-positive’ convention for the thin-lens formula is that the distances are always measured
out from the lens, so positive values of u and v correspond to the object and image being on
different sides of the lens, i.e. a real image.
A virtual image is represented by a negative value of v – in other words it will be on the same side
of the lens as the object.
[Option G]
red giants and supergiants
Red giant stars are large in size and comparatively cool and so red in colour. They are one of the
later possible stages for a star where the source of energy is the fusion of some elements other
than hydrogen. Red supergiants are even larger.
[Option E]
redshift and recession speed of galaxies
Redshift is due to the expansion of the universe. The recession speed of galaxies can be
approximated from the redshift:
Δλ v
≅
λ c
Δλ is the difference between the observed wavelength and the emitted wavelength of EM radiation
in m,
λ is the wavelength of EM radiation as emitted by the source in Hz,
v is the recession speed of the source in m s–1,
c is the speed of EM waves in m s–1.
[Option E]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
redshift
Light from distance stars and galaxies that are receding will show a Doppler shift towards longer
wavelengths. This is known as redshift.
[Option E]
refractive index and critical angle
The refractive index and the critical angle are related:
1
n=
sinC
n is the refractive index of a material,
C is the critical angle (in the material) for total internal reflection to take place on the boundary
between the material and a vacuum.
[Option F]
refractive index
The refractive index of a medium is the ratio between the speed of the wave in a vacuum and the
speed of the wave in the medium.
[Option F]
relativistic addition of velocities
Suppose that, according to an observer in a frame S, the frame of reference S′ is moving past S
with a constant velocity v in the x direction. The frames are on top of one another when t = t′ = 0.
Then:
u –v
u′x = x
u v
1 – x2
c
ux′ is the velocity of an object as measured by frame S′
ux is the velocity of an object as measured by frame S
v is the velocity of the moving object in m s–1
c is the velocity of light in m s–1 (3 × 108 m s–1)
[Option H]
relativistic energy, momentum, rest mass
The equation linking relativistic energy, momentum, and rest mass is:
2
E 2 = p 2c 2 + m0 c 4
E is the total energy of the moving particle in J,
p is the momentum of the moving particle in kg m s–1
m0 is the rest mass of the particle in kg,
c is the velocity of light in m s–1 (3 × 108 m s–1)
Alternative units are:
MeV for energy,
MeV c–1 for momentum,
MeV c–2 for rest mass.
If this is the case, the speed of light is substituted by the symbol c.
[Option H]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
relativistic momentum
The relativistic momentum of a moving particle is given by:
p = γm0u
p is the momentum of the moving particle in kg m s–1,
γ is the Lorentz factor for the moving object (and has no units: it is a number ≥ 1),
m0 is the rest mass of the particle in kg,
u is the velocity of the particle in m s-1.
Alternative units for relativistic momentum are MeV c–1. If this is the case, the rest mass will be
measured in MeV c–2 and the velocity of the particle will be measured relative to c (the speed of
light).
[Option H]
rest mass
The rest mass of an object is the mass of the object as measured in its own frame of reference. It
is an invariant quantity and can be measured in kg. Alternative units for rest mass are MeV c–2. An
object that has a rest mass of x MeV c–2, has an associated rest energy of x MeV.
[Option H]
rods
Rods are light-sensitive cells responsible for scotopic vision (the black-and-white vision that takes
place in dim light). Rods are mainly located away from the centre of the retina. The density of the
rods on the retina peaks approximately 20° away from the centre.
[Option A]
S
sample-and-hold
The analogue output of a sample-and-hold system follows the analogue input. On receiving a
control signal, the output stops varying and retains the same fixed value. The input signal is said to
have been sampled.
[Option F]
satellite communication
Satellite communication is relaying information from source to receiver via an artificial satellite in
orbit around the Earth. Communications are in the high-frequency radio part of the EM spectrum
[Option F]
scattering of electromagnetic (EM) waves
When EM waves enter a medium, they can be transmitted, absorbed, or scattered. The scattering
of EM radiation describes EM radiation that is affected in such a way that the energy being
transferred is spread in all directions.
[Option G]
Schmitt trigger
The output of a Schmitt trigger has two possible values. The voltage on the input, which triggers
the change between these two values, has a different value for a rising signal when compared with
a falling signal. It can be used to reshape digital pulses that have been subjected to noise or
dispersion.
[Option F]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
Schwarzschild radius
The Schwarzschild radius is the distance from the centre of a black hole at which the escape
velocity is equal to the speed of light. It can be calculated from:
2GM
RS =
c2
RS is the Schwarzschild radius in m,
G is the gravitational constant (6.67 × 10–11 N m2 kg–2),
M is the mass of the black hole in kg,
c is the velocity of light in m s–1 (3 × 108 m s–1)
[Option H]
secondary colours
The secondary colours are yellow, magenta, and cyan. They result from mixing together two
primary colours (magenta = red + blue; cyan = blue + green; yellow = red + green).
[Option A]
serial-to-parallel converter
A serial-to-parallel converter converts a single input serial digital line into a parallel digital signal
outputted on several digital lines.
[Option F]
Shapiro experiment
The Shapiro experiment measures the time taken for a pulse of EM radiation to travel to a nearby
planet. The gravitational field of the Sun affects the time taken, and measurements confirm the
predictions of general relativity.
[Option H]
sideband frequencies
The power spectrum of an AM signal will show peak amplitude at the frequency of the carrier
waves. In addition, there will be frequencies above and below the carrier wave frequency for each
frequency that is represented in the signal wave. The collection of frequencies above and below
the carrier wave frequency are collectively known as the sideband frequencies.
[Option F]
signal wave
The signal wave is the information that is being sent from source to receiver, for example the
sound signal that is being broadcast using radio waves.
[Option F]
simultaneity
If two events happen together at the same time we say they are simultaneous. Events that take
place at the same point in space are simultaneous to all observers. Events that take place at
different points in space can be simultaneous to one observer, but not simultaneous to another.
[Option H]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
Snell’s law
When a wave is refracted between two media, the ratio of the angle of incidence to the angle of
refraction is a fixed constant that depends on the speeds of wave in each media:
n1 sinθ 2 v 2
=
=
n2 sinθ1 v 1
n1 is the refractive index of medium 1 (no units),
n2 is the refractive index of medium 2 (no units),
θ2 is the angle of refraction (the angle between the refracted ray and the normal) in medium 2
measured in ° or rad,
θ1 is the angle of incidence (the angle between the incident ray and the normal) in medium 1
measured in ° or rad,
v2 is the speed of the wave in medium 2 in m s-1,
v1 is the speed of the wave in medium 1 in m s-1.
[Option F]
space-time
Space-time is a four-dimensional coordinate system which has the three conventional dimensions
of space (x, y, and z) and a fourth dimension of time (t). An event can be specified by all four
dimensions. All observers agree on the space-time separation between events. Moving objects
always follow the shortest possible path between two points in space-time.
The space-time separation between events is given by:
s 2 = x 2 + y 2 + z 2 – c 2t 2
s is the space-time separation between events in m,
x, y, and z are the distances between the events in the three axis directions in m,
c is the velocity of light in m s–1 (3 × 108 m s–1),
t is the time between the events in s.
[Option H]
special relativity, the two postulates of
The two postulates of special relativity state that the speed of light in a vacuum is the same
constant for all inertial observers and that the laws of physics are the same for all inertial
observers.
[Option H]
spectral class
Stars are classified into different categories depending on their different spectra of light emitted.
The seven main spectral classes (in descending temperature) are O, B, A , F, G, K and M.
[Option E]
spectroscopic binary stars
A spectroscopic binary is a pair of stars whose existence can be deduced from analysis of
variations in the spectrum of the light received. Over time the wavelengths show a periodic shift of
splitting of frequency.
[Option E]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
spectroscopic parallax
It is possible to estimate a star’s luminosity from the relative intensities of different frequencies in
its spectrum. The luminosity and the apparent brightness can be used to estimate the stellar
distance. This process is known as spectroscopic parallax.
The method of spectroscopic parallax is limited to measuring stellar distances less than about
10 Mpc.
[Option E]
spherical aberration
Spherical aberration is the term used to describe the fact that rays striking the outer regions of a
spherical lens will be brought to a slightly different focus point from those striking the inner regions
of the same lens. In general, a point object will focus into a small circle of light rather than a point
image.
[Option G]
spin
Particles with non-integer spin ±
(
1
2
±
3
2
) are called fermions. All leptons and baryons are fermions.
This includes all the ‘everyday’ particles of matter, such as protons, neutrons, and electrons.
Particles with integer spin (0, ± 1, ± 2) are called bosons. All mesons are bosons, as are photons,
and the other exchange particles, for example gluons.
[Option J]
standard candles
‘Standard candle’ is a term used to describe a source of known luminosity used to make
comparisons and estimate other sources of luminosity that are at equivalent distances; for
example, if the luminosity of one star in a galaxy is known, then the luminosities of all the other
stars in that galaxy can be estimated.
[Option E]
Stefan–Boltzmann law
The equation for the total power radiated in black-body radiation is:
P = σAT 4
P is the total power radiated by the black body in W,
σ is the Stefan–Boltzmann constant (5.67 × 10–8 W m–2 K–4),
A is the surface area in m–2,
T is the absolute temperature of the black body in K.
[Option E]
stellar cluster
A stellar cluster is a group of stars that are in close relative proximity to one another.
[Option E]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
stellar parallax
Stellar parallax is the apparent movement (when compared to the ‘fixed’ background of stars) of
nearby stars over the course of a year. It is a result of the movement of the Earth during the year.
The measured amplitude of the angle variation is called the parallax angle for the star and can be
used to calculate its distance:
1
d=
p
d is the distance from the Earth to the star in pc,
p is the parallax angle of the star in seconds of arc,
1 o.
(3600
)
[Option E]
step-index optical fibre
An optical fibre with a very narrow core is known as a step-index optical fibre. Pulses of EM waves
can be transmitted along the core of the fibre.
[Option F]
strangeness
Strangeness is a property carried by the strange quark. Strange quarks have a strangeness of –1,
whereas antistrange quarks have a strangeness of +1. Strangeness will be conserved in
electromagnetic and strong interactions.
[Option J]
string theory
String theories regard elementary particles not as points but as strings. The different quantum
properties correspond to different modes of vibration of the string. These models are formulated in
more dimensions than the four dimensions of the standard model – typically 10. The extra
dimensions cannot be perceived as they are curved into a very compact space whose typical linear
size is unobservable small.
[Option J]
strong force in terms of colour force
The colour interaction is the fundamental interaction that binds quarks together into baryons and
mesons. The residual strong interaction is the force that binds colour neutral particles (such as the
proton and neutron) together in the nucleus.
[Option J]
supernova
A supernova is the catastrophic final end of a red giant star – most of the mass of the star is
ejected in a violent explosion.
[Option E]
synchrotron
In a synchrotron, charged particles move in an approximately circular path of large radius inside an
evacuated pipe. Magnets and p.d.s are used to accelerate the particles.
[Option J]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
T
temperature change of the universe since the Big Bang
The temperature of the universe was 1032 K at 10–43 s after the Big Bang and is 2.7 K at present.
[Option J]
therapeutic applications
Therapeutic applications are medical procedures designed to cure or relieve the suffering of a
patient.
[Option I]
thin air wedge
A thin air wedge is the gap between the two surfaces of two glass plates that are at a small angle
to one another.
[Option G]
thin lens formula
The following applies to thin lenses using the ‘real-is-positive; convention:
1 1 1
= +
f v u
f is the focal length of the lens in m
v is the image distance in m
u is the object distance in m
[Option G]
three family structure of quarks and leptons
Quarks and leptons both come in three ‘families’ or ‘generations’:
Quarks
Leptons
1
U, D
e, νe
2
C, S
μ, νμ
3
T, B
τ, ντ
[Option J]
time dilation close to a black hole
The time dilation factor equation for an object close to a black hole is:
Δt 0
Δt =
R
1− S
r
Δt is the time interval between events in s as observed a long distance away from the black hole,
Δt0 is the (proper) time interval between events in s as observed near the black hole,
RS is the Schwarzschild radius in m,
r is the distance away from the black hole in m.
[Option H]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
time dilation formula
The time interval between two events, recorded by a moving clock, is less than the time recorded
by a clock for which the two events take place at the same point of space. This effect is known as
time dilation. The time dilation formula is:
Δt = γΔt 0
Δt is the time interval recorded in s in the frame in which the events take place at different points in
space,
γ is the Lorentz factor for the moving frame (and has no units: it is a number ≥ 1),
Δt0 the proper time interval recorded in s.
[Option H]
time-division multiplexing
Time-division multiplexing is a technique that allows several signals to be sent along the same
channel of communication at the same time. It uses the time between the samples of one message
to send samples from other messages.
[Option F]
total energy of a moving object
The total energy of a moving object is greater than its rest energy:
E0 = γm0 c 2
E0 is the rest energy of a mass in J,
γ is the Lorentz factor for the moving object (and has no units:it is a number ≥ 1),
m0 is the rest mass in kg,
c is the velocity of light in m s–1 (3 × 108 m s–1).
[Option H]
total internal reflection
Total internal reflection takes place when a ray meets the boundary between two media heading
from a more optically dense medium towards a less optically dense medium, with an angle of
incidence that is greater that the critical angle. The ray cannot be refracted so it must stay within
the optically denser medium and is reflected off the boundary.
[Option F]
transmission of electromagnetic (EM) waves
When EM waves enter a medium, they can be transmitted, absorbed, or scattered. The
transmission of EM radiation describes EM radiation that passes through a medium unaffected.
[Option G]
tuning circuit
A tuning circuit is one that responds to preferentially amplified signals at a given frequency.
Typically, a capacitor and an inductor are used to create a circuit with its own natural frequency of
oscillation. If this circuit is stimulated at its natural frequency, then resonance occurs and the
oscillations are greatly increased in amplitude.
[Option F]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
twin paradox
One of two twins undertakes a journey in a space ship that involves travelling at a high speed away
from the Earth and then back to the Earth. The other twin stays on the Earth. According to the twin
on Earth, the twin in the space ship is moving, so time must run slowly for the twin on the space
ship and they must age less. According to the twin on the spaceship, the twin on Earth is moving
so it would seem that the time must run slowly for the twin on the Earth and they must age less.
The paradox is that they both cannot be right. Since the twin in the spacecraft makes an outward
and return journey, this is no longer a symmetrical situation for the twins – the twin in the
spacecraft will age less.
[Option H]
U
ultrasound
Ultrasound is sound waves at a frequency above that of human hearing.
[Option I]
uncertainty principle
The uncertainty principle, in terms of time and energy, allows for the creation of a particle with
energy ΔE to exist no longer than a time Δt as given by:
h
ΔEΔt ≥
4π
ΔE is the uncertainty in energy in J,
Δt is the uncertainty in time in s,
h is Planck’s constant (6.63 × 10–34J s).
[Option J]
up-link frequency
Different frequencies are used for sending information to and from a satellite. The up-link
frequency is the frequency used for sending information to a satellite.
[Option F]
V
virtual image
A virtual image is one in which the rays of light do not pass through the image. It cannot be
projected onto a screen.
[Option G]
virtual particles
A virtual particle is one that only exists for a short enough time for the uncertainty relationship to
allow for their existence. They are involved in Feynman diagrams but cannot be physically
detected.
[Option J]
© Oxford University Press 2010
IB Physics Course Companion
Glossary of terms from option chapters
W
wedge films
The conditions for interference in wedge films are:
Constructive interference:
2nt = mλ
Destructive interference:
1⎞
⎛
2nt = ⎜ m + ⎟λ
2⎠
⎝
n is the refractive index of the medium in the wedge (no units),
t is the thickness of the wedge at the point being considered in m,
m is an integer (1, 2, 3, etc.),
λ is the wavelength of light in m.
[Option G]
white dwarfs
White dwarf stars are small in size and comparatively hot so white in colour. They are one of the
final possible stages for a star being a hot remnant that is cooling down without any fusion
reactions taking place.
[Option E]
Wien’s displacement law
Wien’s displacement law relates the wavelength at which the intensity of radiation is a maximum to
the temperature of the black body:
2.90 × 10 −3
λmax =
T
λmax is the wavelength at which the intensity of radiation is a maximum in m,
T is the absolute temperature of the black body in K.
[Option E]
WIMPs
Weakly Interacting Massive Particles (WIMPs) are one possible theoretical explanation for dark
particles.
[Option E]
wire chamber
A wire chamber is a particle detector involving very many fine wires held a few millimetres apart
from one another with large p.d.s between them. The ionizations, caused by particles travelling
through the detector, trigger small pulses of current which can be recorded and analysed to identify
the path taken by the particle.
[Option J]
wire pairs
Wire pairs are two wires used directly to connect the sender and receiver of information.
[Option F]
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IB Physics Course Companion
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