Download period ____ due date

Fourth Quarter Notes
Light & Optics Unit
light
electromagnetic spectrum
electromagnetic radiation
Huygens principle
Planck’s proposal
Einstein’s idea
A range (frequencies) of the electromagnetic spectrum which can be detected by the human eye.
Phrase used to describe electromagnetic radiation of all wavelengths and frequencies. This includes
radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays, etc.
Waves which can move through a vacuum because they are self propagating (causing their own
continuation). They self propagate by using changing electric fields which generate changing
magnetic fields which generate changing electric fields and so on
Light must be made of waves this explains diffraction.
Proposed energy is made-up of packets of energy (particles) called quanta. He did this to explain
blackbody radiation.
Einstein described the photoelectric effect as particles of light called photons bumping the electrons
off. This led to the dual nature of light principle.
wave or particle (duality of light)
Light is both a particle and a wave.
luminous source
An object that emits light.
illuminated source
Object that is visible as a result of light reflecting off of it.
transparent
Media which transmits light.
translucent
Media which transmits light but does not allow objects to be seen.
opaque
Media which does not allow light to transmit through it.
additive colors
Colors which when combined optically form white. (luminous sources)
This process is used for film and television.
additive primary colors
red, green, and blue (RGB)
additive secondary colors
cyan, magenta, yellow
subtractive colors
Colors which combined, usually by mixing pigments, form black. (illuminated sources)
This process is used in printing and art.
subtractive primaries (or primary
pigment)
cyan, magenta, and yellow (CMY) or blue, red, and yellow
photometry
Measuring light.
luminous intensity
Amount of light used to define the base metric unit, candela (cd). One candela was defined as the
light
candela, cd
metric unit of light intensity
luminous flux
The rate of energy (energy per time or power) in the form of visible light is emitted by a luminous
source. Note: Most luminous sources have an output consisting of a lot of infrared light, this is not
included in this measurement.
lumen, lm
metric unit of luminous flux
illuminance
The measurement of the amount of light that
strikes a surface.
lux, lx
speed of light
FORMULA: wave speed for
electromagnetic waves
metric unit on illuminance,
1 lux = 1 lumen per meter squared
300,000 kilometers per second or 186,000 miles per second
symbolized by c (lower case)
c=λ·f
E=
P
4π r 2
ray model of light
The use of rays (lines with arrows on one end as in geometry) to represent light waves.
polarization
The use of filters to limit waves to only one plane of travel. Filters may be naturally occurring or
man-made.
reflection
When a waves bounces off of a surface.
specular reflection
Mirror-like reflection, a high degree of reflection with little scattering.
diffuse reflection
Reflection with a lot of scattering.
diffusion
The scattering of light in many directions.
incident ray
Incoming light ray.
“I” in the diagram.
reflected ray
Outgoing light ray.
“R” in the diagram.
normal line
A line perpendicular to the surface of reflection
or refraction. “N” in the diagram
angle of incidence
Angle between the incident ray and the normal line.
angle of reflection
Angle between the reflected ray and the normal line.
law of reflection
angle of incidence = angle of reflection
plane mirror
A flat mirror. Images formed by plane mirrors are virtual, upright, left-right reversed, the same
distance from the mirror as the object's distance, and the same size as the object.
object
The person or thing reflected in the mirror.
real image
An image formed in front of a mirror. Light converges to form real images. Real images can
be projected.
virtual image
An image formed behind a mirror. Virtual images are formed where light does not reach.
concave mirror
A spherical mirror which is curved towards the object.
principal axis
focal point
focal length
A line from the center of curvature of a mirror to
the object.
The point of focus of a mirror. “F” in the
diagram.
The distance from the focal point to the mirror.
1 1 1
=
+
f do di
do, distance to object
di, distance to image
f, distance to focus
FORMULA: mirror equations
h
d
M= i = − i
ho
do
spherical aberration
ho, height of object
hi, height of image
M, magnification
Image defect of spherical mirrors which does not allow parallel light rays to converge at the focal
point. Produces a fuzzy image.
magnification
The factor of enlargement.
convex mirror
A spherical mirror which is curved away from the object.
refraction
The bending of a wave when it passes from one medium to another.
optical density
optical refraction
The property of a transparent material that is an inverse measure of the speed of light through the
material.
The bending of light rays as they pass obliquely from one medium into another of different optical
density.
index of refraction
FORMULA: Snell’s law
The ratio of the speed of light in a vacuum to the speed of light of the medium in question.
n1·sinθ1 = n2·sinθ2
n1, index of refraction of one material
n2, index of refraction of second material
θ1, angle of incidence
θ2, angle of refraction
lenses
Transparent material with two nonparallel surfaces. Surfaces can be spherical, parabolic, cylindrical,
or flat.
diverging lens
A lens which causes light rays to spread out from
the focal point.
converging lens
A lens which causes light rays to spread in at the
focal point.
1 1 1
=
+
f do di
FORMULA: lenses
chromatic aberration
total internal reflection
h
d
M= i = − i
ho
do
do, distance to object
di, distance to image
f, distance to focus
ho, height of object
hi, height of image
signs:
hi is negative for an inverted
image
di is negative for a virtual
image (same side of lens as the
object)
f is negative for diverging lens,
positive for converging lens.
Color distortion in an image produced by a lens, caused by the inability of the lens to bring the
various colors of light to focus at a single point.
M, magnification
A refraction event that causes a “perfect” reflection inside of a material.
critical angle
interference
diffraction
An angle of incidence that will produce an angle of refraction of 90º.
Any angle greater than the critical angle will cause total internal reflection.
The interaction of two or more waves with each other interaction of two or more waves with each
other.
The bending of waves through an opening or around small objects. Since diffracted light interferes
with itself, it was considered proof that light travels in waves.
scattering
A beam of light cannot be seen unless it is scattered by particles.
lasers
A light which produces a coherent beam of light in which all of the waves have identical frequency
and wavelength and are in phase with each other.
Nuclear Physics Unit
The three subatomic parts of an atom, their charges and where they are located.
a) proton
b) neutron
c) electron
elements
isotopes
The positively charged atomic particle which is located in the center or nucleus of the atom.
The number of protons designates the atomic number which determines the unique nature of the
The atomic particle of no charge which is located in the center or nucleus of the atom.
The neutron is believed serve a function of holding the nucleus together.
The negatively charged particle which can be found in regions of high probability outside
of the nucleus.
A substance composed of atoms having an identical number of protons in each nucleus.
There are 92 naturally occurring elements and 23 artificially, laboratory created elements.
Atoms of the same atomic number or element but different numbers of neutrons.
Some isotopes are stable and last indefinitely. Some are unstable and decay.
ions
Atoms which do not have the same number of protons and electrons and, therefore, have a charge.
atomic number
The number of protons in an atom. Also the number of the element.
symbol: Z
mass number
The number of protons and neutrons in an atom.
symbol: A
atomic mass
Weighed average of all the isotopes of an element.
Blackbody Radiation.
Objects will glow at colors which depend on their temperatures. The objects start to glow at the long
wavelength colors (red) and continue to shorter wavelengths (ultraviolet) as the temperature increases.
Objects stop moving to shorter wavelengths once they reach UV even if the temperatures increase.
This is referred to as the “UV catastrophe”.
Photoelectric effect.
A metal surface emits electrons when light of certain frequencies shines on it.
Planck’s formula
energy = Planck’s constant * frequency
E=n·h·f
n can be 1, 2, 3, 4, ….
Planck’s constant
h = 6.63 x 10-34 J·s
Historic Summary
a) J.J. Thompson’s idea
b) Rutherford’s idea
c) Planck’s idea
d) Einstein’s idea
Discovered the electron and proposed the “plum pudding” model of the atom. Think of blue berry
muffins with the electrons as blue berries.
Rutherford shot alpha particles at gold foil. Most of the alpha particles went through but some
bounced back which indicated a dense nucleus surrounded by empty space. This led him to propose
the “planetary model” of the atom.
Proposed energy is made-up of packets of energy (particles) called quanta. He did this to explain
blackbody radiation.
Einstein described the photoelectric effect as particles of light called photons bumping the electrons
off. This led to the dual nature of light principle.
e) Bohr’s idea
Explained the spectra of atoms by using Planck’s quanta. Also proposed Bohr’s model of the atom.
f) De Broglie’s idea
All particles have wave properties.
g) Schrödinger & Heisenberg’s
idea
Introduced uncertainty and probability to the study of the atom and the quantum mechanical model.
strong nuclear force
The force that holds the nucleus together. One of four forces of nature.
mass deficit/binding energy
The mass of the nucleus is less than the sum of its parts. This difference is the mass deficit. It is held
as energy that holds the nucleus together. This is the binding energy.
atomic mass unit to megaelectron volt conversion
931.494 mega-electron volts = 1 atomic mass unit
Radioactivity
Why do isotopes decay?
Because they are unstable.
parent
Unstable isotopes before they decay.
daughter
Unstable isotopes after they decay and transmute into something else.
half-life
The time it takes for half of the original amount to decay. It is different for different isotopes.
half-life curve
No is the original amount of atoms.
N is the current amount of atoms.
k is the radioactive decay constant which is substance dependent.
t is time.
half-life formula
N = N 0e
radioactivity
Spontaneous emission of energy or radiation.
kt
three types of radiation
a) alpha particle, α
4
+2
2 He
b) beta particle, β
An electron or positron. A sheet of aluminum foil offers protection.
c) gamma particle, ɣ
A high energy photon. No mass and no charge. One inch of lead offers protection.
, a helium nuclei. A sheet of paper offers protection.
units of radioactive decay
becquerel
Unit of radioactive decay. 1 becquerel (Bq) = 1 decay/second
curie
Unit of radioactive decay. 1 currie (Ci) = 3.7 x 1010 decays/second
nuclear decay series
If the daughter nucleus is stable the decay process ends, if it is unstable the process continues.
Nuclear Reactions
nuclear fission
Breaking an atom apart.
chain reaction
Neutrons released by fission can then cause more nuclei to fission.
controlled chain reaction
The process that is used in a nuclear power plant.
uncontrolled chain reaction
The process that is used in a nuclear bomb.
nuclear fusion
Smashing atoms together.
radiometric dating
The use of radioactive isotopes to determine the age of archeological and geological samples.