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P1b revision
Topic 11 Now you see it, now you don’t
1. Transverse and Longitudinal waves
2. Amplitude, Frequency, Wavelength
Digital signals only have two amplitudes. Analogue have many.
3. Speed = Distance
Time
and
Speed = Frequency x Wavelength
4. Electromagnetic waves : are transverse
 travel at the speed of light
 3x108 m/s in a vacuum
 have different wavelengths and frequencies
 radio, micro, infra red, visible light, ultra violet, X, gamma
5. Uses : radio waves for communication ( via antennae )
microwaves for communication ( via dishes ) and heating water
infra red waves for heating, remote controls, thermal imaging cameras
visible light for communications ( via optical fibres ) endoscopy
ultraviolet waves for scanning bank notes, suntanning
X waves for scanning bones and teeth
Gamma waves for medical diagnosis and treatment
6. Dangers : heating effect of microwaves and infrared waves
ionising effect of ultraviolet, X and gamma
7. Sound waves : are longitudinal
 travel at the speed of sound
 330 m/s in air at 0oC
 can be heard if between 20 and 20kHz
 above 20kHz are called ultrasound
8. Uses of ultrasound : measuring the depth of the sea and detecting fish
scanning unborn babies
detecting cracks in structures
9. Earthquake waves are longitudinal (P) waves that can travel through the
liquid outer core or transverse (S) waves that can’t
Topic 12 Space
1. Stars, Planets, moons, asteroids, meteors, meteorites, comets
2. Solar System, Galaxy, Universe
3. Distance from Sun to Earth = 1a.u. A light year is how far light travels in 1 year
4. Conditions required for life : The right temperature ( between 1 and 35oC to permit water to exist )
 An atmosphere ( protects us from meteors ) of oxygen
 A gravitational field strength capable of holding down an atmosphere
5. Travelling in space : Escaping the Earth requires you to travel at 11km/s
 You have to carry or have the means of producing oxygen
 You can create gravity by spinning your spacecraft – avoids muscle wastage
 You have to produce electricity for life support systems / computers
Solar cells, Fuel cells, Nuclear fuel cells
6. Newton’s 3rd law : if A pushes B with 2N, B pushes A back with 2N
Allows us to get our rocket off the ground
Newton’s 2nd law : an unbalanced force F causes acceleration and a = F/m
Newton’s 1st law : balanced forces mean constant speed
7. Life cycle of a star
8. Spectra
When light from a star is observed through a diffraction grating, black
absorption lines appear according to the elements that are present in the star.
More distant stars or galaxies show the same lines moved towards the red end
of the spectrum ( their wavelength appears longer ) – red shift
When an ambulance approaches you the frequency of its siren increases.
If frequency increases, wavelength decreases.
If starlight shows a lengthening of wavelength ( decrease of frequency ) it must
mean the star or galaxy is moving away from us.
9. Big Bang theory
 states the Universe is expanding and at the beginning of time it must have been
in a small space.
 is backed up by observations of red shift
 in 1965, Arno Penzias and Robert Wilson’s observations of background
microwave radiation suggested the Universe is at the same temperature as
that which would be expected if it was cooling down from a Big Bang
 replaces the previously thought Steady State theory that the Universe had no
beginning and no end.
 Oscillating theory suggests that gravity will eventually stop the expansion and
cause the Universe to contract again – Big Crunch – and then maybe explode
outwards in another Big Bang and so on.
Scientists will know more when they finally determine the mass of the
Universe. Currently, Dark Matter ( emits no EM waves so is hard to detect )
hinders the calculation.