Electromagnetic Waves v2

Question 1

electromagnetic waves (2 key facts and 1 eg of one of these facts)

Answer 1

• transverse waves
• transfer energy from the source of the waves to an absorber
  eg: infrared waves emitted from a hot object transfer thermal energy

Question 2

order of electromagnetic spectrum

Answer 2

visible light is red -> violet

Question 3

speed of electromagnetic waves

Answer 3

all types of electromagnetic wave travel at the same velocity through a vacuum or air
3 x 10⁸m/s through a vacuum

Question 4

fill in the blanks

Different substances may [4 things] electromagnetic waves in ways that vary with ………..
Some effects, for example …………, are due to the difference in velocity of the waves in different substances.

Answer 4

Different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength.
Some effects, for example refraction, are due to the difference in velocity of the waves in different substances.

Question 5

examples of EM waves being produced by changes inside an atom/nucleus

Answer 5

• gamma rays are produced by changes in the nucleus of an atom
• when electrons in an atom move down between energy levels, they emit EM waves

Question 6

properties of radiowaves

Answer 6

Radio waves can be produced by oscillations in electrical circuits.
- to produce at a specific frequency - the oscillations must have the frequency you want the waves to have

When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit.

Question 7

use of radio waves and why

Answer 7

television and radio signals
- can travel long distances through air
- longer wavelengths can bend around obstructions to allow detection of signals when not in line of sight

Question 8

2 uses of microwaves and why

Answer 8

satellite communications
- can pass through Earths’ atmosphere to reach satellites
cooking food
- can penetrate into food and are absorbed by water molecules in food, heating it

Question 9

2 uses of infrared and why

Answer 9

infrared cameras
- all hot objects emit infrared waves - sensors can detect these to turn them into an image

electrical heaters & cooking food
- can transfer energy quickly to heat rooms and food

Question 10

use of visible light and why

Answer 10

fibre optic communications
- short wavelength means visible light carries more information

Question 11

use of ultraviolet and why

Answer 11

energy efficient lights & artificial sun tanning
- carries more energy than visible light
- some chemicals used inside light bulbs can absorb UV and emit visible light

Question 12

2 uses of X rays & gamma rays and why

Answer 12

medical imaging
- pass easily through flesh, but not denser materials like bone
treatments
- high doses kill living cells, so can be used to kill cancer cells - gamma rays can also be used to harm bacteria

Question 13

hazards associated with UV

Answer 13

can damage skin cells, causing skin to age permaturely and increasing the risk of skin cancer, and can cause blindness

Question 14

hazards associated with X-rays & gamma rays

Answer 14

forms of ionising radiation
- can damage or kill cells, cause mutation of genes, lead to cancers

Question 15

hazards of radiowaves & microwaves

Answer 15

can penetrate the body and cause internal heating

Question 16

hazards of infrared and visible light (2 different ones)

Answer 16

infrared can damage or kill skin cells due to heating
visible light can damage the retina

Question 17

wavefront diagrams

Answer 17

the wave front is an imaginary line at right angles to the direction the wave is moving

For a given frequency of light, the wavelength is proportional to the wave speed:
wave speed = frequency × wavelength
So if a wave slows down, its wavelength will decrease. The effect of this can be shown using wave front diagrams, like the one below. The diagram shows that as a wave travels across a boundary from air to water it slows down and the wavelength decreases. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.

Question 18

explaining refraction

Answer 18

In this diagram, light waves move from air into water. Light waves move slower in water. The right hand side (the bottom edge) of the incoming wave slows down before the left hand side does. This causes the wave to change direction.