Download Physics 1b - The Thomas Cowley High School

Physics 1b
1. The Electromagnetic spectrum
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c.
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d.
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e.
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Shortest
Gamma rays
X-rays
Ultra Violet
Visible light
Infra red
Microwaves
Radio waves
Longest
Wave length
General
Electromagnetic radiation are Electric and Magnetic disturbances,
travel as waves through space( vacuum) at 300million m/s
Wave speed (m/s) = frequency Hertz (Hz) X wavelength metres
Gamma rays and X rays
Gamma rays have the shortest wavelength and highest frequency
absorbed by dense materials such as bone and metal
damage living tissue when they pass through
X-rays used in hospitals for radiographs. Staff wear lead aprons
& stand behind screens – they wear film badges to monitor exposure
Gamma rays used to kill harmful bacteria in food, sterilising surgical equipment and
kill cancer cells
Richard
Light and Ultra Violet radiation
Of
York
UV causes tanning, over exposure can harm skin and eyes
Gave
UV Used in security markers
Battle
Visible light detected by eyes. Different wavelengths seen as different
In
colours. Can be transmitted down optical fibres
Vain
Infra-red, microwaves and Radio waves
Infra red – given out by all hot objects. We sense it as heat & it can burn. Uses –
Toasters, grills, radiant heaters, TV remotes -Night vision equipment detects it
Microwave ovens produce frequencies that are absorbed by water molecules in
food, cooking it from the inside out
Microwave transmitters produce wavelengths that are able to pass through
atmosphere, used to send signals to & from satellites and within mobile phone
networks
Radio waves used to transmit radio & TV programmes
Communication
Different frequencies are used for different applications – Local, national,
international, emergency services and amateur radio, terrestrial TV, Satellite TV, mobile phones
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Optical fibres are thin glass fibres; they can be bent around curves. Light or
infra red radiation is transmitted along fibre by total internal reflection (TIR)
Analogue signals vary continuously in amplitude. Digital signals are either on (1) or
off (0).Compared to analogue signals digital ones are free of noise and distortion.
AND They are able to carry much more information
2.Radioactivity (you need to know basic structure of atoms – Chemistry 1a)
a.Isotopes. Atoms of an element always have the same number of protons Isotopes
have different numbers of neutrons E.g Carbon C12 C14
6
12
C
6 Protons and 6 Electons
6 Protons + 6 neutrons = 12
6 protons + 8 neutrons = 14
6
C
14
Radioactive substances contain unstable nuclei, they may become stable by
emitting radiation
 Random – not affected by external conditions like heat/ pressure/catalysts
b.Three types -Alpha particles (α), Beta particles (β) and Gamma radiation (γ)
 Alpha – A Helium nucleus (2 protons & 2 neutrons). Stopped by paper or few cm
of air. Strongly ionising. Collisions with atoms can “knock off” electrons –
producing ions. Has a positive charge and is deflected by electric & magnetic
fields.
 Beta – high speed electrons. Stopped by thin metal or about 1m of air. Has a
negative charge -deflected by electric and magnetic fields. Less ionising than α,
but more penetrating.
 Gamma – electromagnetic waves. Have an unlimited range in air, stopped by thick
lead. Weakly ionising, but strongly penetrating. Not deflected by either magnetic
or electric fields
c. Half life.
 Time taken for the number (& therefore mass) of parent atoms in a sample to
halve – Also for count rate to fall to half the initial level.
Count
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Time
d.Uses
 Alpha – smoke alarms. Beta – control of thickness of materials like paper in
manufacturing. Gamma & Beta – tracers in medicine. Gamma – sterilisation –
medical equipment and perishable foods
3. Origins of Universe
Our Galaxy, the milky-way contains about 100,000 million stars, there are millions of
galaxies in the Universe
a.Red shift – Light from distant galaxies is red-shifted to longer wavelengths, the
further the galaxy the greater the red shift.
b.The Big Bang
 Red shift shows us that distant galaxies are moving away from us. An Expanding
Universe
 Universe started with a massive explosion from a small point “Big Bang” theory
c.Looking into space
 Telescopes are able to detect visible light or other electromagnetic radiation (X
rays, radio-waves)
 Telescopes on satellites do not have distortion caused by earths atmosphere &
have grater detail