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X-rays are used
in hospitals to
take radiographs.
X-rays and gamma
rays damage living
tissue when they
pass through it.
Large doses can kill
cells, small doses
can cause cancer
Gamma rays
•Have the shortest
wavelengths
• used to kill
bacteria in food,
sterilise surgical
equipment and kill
cancer cells.
Microwaves
•Short waves
•Can pass through
atmosphere for satellite
communications
•Used in cooking, microwave
ovens - heat water molecules
Infrared-IR
•All objects emit IR. The hotter
the object the more IR it emits
•IR heat objects.
•Uses: heaters, IR scanners, IR
cameras, remote controls, optical
fibres and communications
X-rays and gamma rays are absorbed
by dense material such as bone and
metal but pass through soft tissue
Radio waves
•Have the longest wavelengths
•Used in communications
•Radio waves - smallest long waves 300,000Hz+
•Carry radio, TV, mobile phone signals
•Alternating voltage  ariel  receiver
•Frequency of radio wave = alternating
voltage of carrier wave
•High frequency radio waves•Carry more information
•Have a shorter range
•Less diffraction
Optical Fibres
•Visible light and IR carry
signals
•Carry more info than wires
•More secure, signal stays in
wire
Radio waves are
reflected by the
IONOSPHERE.
Stronger in
summer
All EM waves travel through space at speed of
light (300 million m/s).
Wave speed= Frequency X Wavelength
(m/s)
(Hz)
(m)
P1b, Physics
Analogue signals vary
continuously in amplitude or
frequency
Digital signals are on or off.
Digital signal free of
interference and carry more
information.
Carrier waves (radio,
microwaves etc) carries
digital/analogue signal
Ultraviolet-UV
Found naturally in sunlight.
UV harms the skin and
eyes, causes a sun tan, used
in security markers
The use of
radio waves
depends on
the frequency
of the waves
Marie CurieDiscovered
Radioactivity.
Worked with
uranium. Died of
cancer because
of her work.
Alpha particle
Positive charge, deflected in magnetic and
electric fields, Helium nucleus
Beta particle
Negative charge, deflected in magnetic
and electric fields, electron emitted from
nucleus
Gamma particles
No charge, not deflected in magnetic and
electric fields, EM wave
A radioactive substance
contains unstable nuclei.
An unstable nucleus
becomes stable by
emitting radiation.
Alpha Radiation- Stopped by paper or a
few cm of air
Beta Radiation– Stopped by thin aluminium
or about 1m of air
Gamma radiation- Stopped by thick lead or
concrete and has an unlimited range in air
Unstable radioactive elements decay
randomly and give off particles
Isotope atoms of an element have
different numbers of neutrons
Detect radiation with Geiger Muller
Tube (GM tube)
Isotopes
Different
types of
atoms of
the same
chemical
element,
each having
a different
number of
neutrons
•Light from distant galaxy is redshifted to longer wavelengths
•Edwin Hubble discovered that light
from galaxies were red-shifted
•Distant galaxies are moving away
from us
•Speed of distant galaxy is
proportional to distance from us
The universe is expanding
Half life
Time it takes for number of
radioactive nuclei of the isotope to
decay to half its initial value.
Ionisation- Alpha and beta particles
knock electrons out of atoms
Uses of radioactivity
•Automatic thickness monitoring- uses beta
•Radioactive tracers- uses gamma
•Radioactive carbon/uranium dating
•Carbon- wood
•Uranium- rocks
•Smoke detectors- uses alpha
Big Bang (BB)Theory
•Massive explosion from a
small point
•Background microwave
radiation is radiation
created just after the BB.
•Created as high energy
gamma radiation after BB
As universe expanded, it
stretched into longer and
longer wavelengths.
P1b Physics
•Space, time and matter created
by the Big Bang
•BIG BANG happened 13,000
million years ago
The Earths atmosphere
absorbs all electromagnetic
waves, except visible light,
radio waves and some UV
radiation.
Satellite detectors are used
to make observations outside
the visible and radio spectrum.
Clear images are observed
using telescopes on satellites
detecting visible light.
The most distant galaxies are
about 13 million light years away.