The seven groups in order, what they have in common, how frequency and wavelength change across the spectrum, and the required practical on infrared radiation.
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1.What type of wave are all electromagnetic waves?
Transverse.
2.How fast do electromagnetic waves travel in a vacuum?
All at the same speed, about 3 x 10 to the power 8 metres per second.
3.Do electromagnetic waves need a medium?
No. They can travel through a vacuum, which is why light reaches us from the Sun.
4.List the seven groups from longest to shortest wavelength.
Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays.
5.Which group has the lowest frequency?
Radio waves.
6.Which group has the highest frequency?
Gamma rays.
7.What is the relationship between frequency and wavelength across the spectrum?
As frequency increases, wavelength decreases, because the speed is the same for all of them.
8.Why is the electromagnetic spectrum described as continuous?
The groups merge into one another. The boundaries between them are not sharp divisions.
9.Which groups are ionising?
Ultraviolet, X-rays and gamma rays.
10.What does ionising mean?
The radiation carries enough energy to knock electrons off atoms, which can damage cells.
11.Which part of the spectrum can the human eye detect?
Visible light, a very narrow band between infrared and ultraviolet.
12.List the colours of visible light from longest to shortest wavelength.
Red, orange, yellow, green, blue, indigo, violet.
13.How are radio waves produced?
By oscillations in electrical circuits.
14.What happens when radio waves are absorbed by a conductor?
They create an alternating current with the same frequency as the wave, which is how they are received.
15.What can changes in atoms and their nuclei produce?
Electromagnetic waves over a wide frequency range, including gamma rays from the nucleus.
16.What determines the effect of an electromagnetic wave on the body?
Its frequency, since higher frequency means more energy per wave.
17.In the required practical, what is investigated?
How the amount of infrared radiation absorbed or emitted by a surface depends on the nature of that surface.
18.Which surface is the best emitter of infrared radiation?
A matt black surface.
19.Which surface is the worst emitter?
A shiny silver surface.
20.Which surface is the best absorber of infrared radiation?
A matt black surface, which is also the best emitter.
21.What apparatus is used for that practical?
A Leslie cube filled with hot water, with different surfaces, and an infrared detector at a fixed distance.
22.Why must the detector be the same distance from each surface?
Intensity falls with distance, so a different distance would change the reading for reasons other than the surface.
23.Why are marathon runners wrapped in shiny blankets?
A shiny surface is a poor emitter of infrared, so it reduces energy transferred away from the body.
24.Why are the backs of fridges often painted black?
A matt black surface is a good emitter, so it transfers energy away more effectively.
25.What happens to the wavelength of an electromagnetic wave entering glass?
It decreases, because the wave slows down while its frequency stays the same.
26.Which travels faster in a vacuum, red light or gamma rays?
Neither. All electromagnetic waves travel at the same speed in a vacuum.
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