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Science Notes for Exam
1) The electromagnetic spectrum (in order of increasing wavelength
and decreasing frequency) is: Gamma and X-rays, ultraviolet, visible
light, infra-red, microwaves and radio waves.
2) All electromagnetic waves travel through space at a speed of 300
3) Wave speed= Wavelength X Frequency
Wavelength= Wave speed / Frequency
Frequency= Wave speed / Wavelength
Frequency is measured in Hertz (H)
Wave speed is measured in Metres per second (M/s)
Wavelength is measured in Metres (M)
4) The Wavelength is the distance from one wave peak to the next
wave peak along the waves.
5) Electromagnetic waves are electrical and magnetic disturbances
that transfer energy from one place to another.
6) The frequency of electromagnetic waves of a certain wavelength is
the number of complete waves passing a point each second.
7) X-rays and gamma radiation are absorbed by dense materials in the
bone and by 2metal.
8) X-rays and gamma radiation damage living tissue when they pass
9) X-rays are used in hospitals to take radiographs.
10) Gamma rays are used to kill harmful bacteria in food, to sterilise
surgical equipment and to kill cancer cells.
11) Ultraviolet radiation harms the skin and the eyes.
12) Colours in the electromagnetic spectrum are Red, Orange, yellow,
green, blue, indigo and violet. (In order of radio waves down to
13) Optical fibres are very thin glass fibres. We use them to transmit
signals carried by light or infra-red radiation. The light rays can't
escape from the fibre. When they reach the surface of the fibre,
they are reflected back into the fibre. Optical fibres carry much
more information-this is because the frequency of light and
infra-red radiation is much higher, optical fibres are more secure
because the signals stay in the fibre.
14) Analogue signals vary in amplitude.
15) Digital signals are either high 1 or low 0.
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Digital transmission when compared with analogue transmission is
free of noise and distortion. It can also carry much more
17) A radioactive substance contains unstable nuclei.
18) An unstable nucleus becomes stable by emitting radiation.
19) There are 3 main types of radiation from radioactive substances-
alpha, beta and gamma radiation.
20) Radioactive decay is a random event-we cannot predict or
influence when it will happen.
21) Alpha radiation is stopped by paper or a few centimetres of air.…read more