Chapter 6: Waves

Question 1

What is an electromagnetic wave?

Answer 1

Oscillating electric and magnetic fields that move at the speed of light

Question 2

What do all waves do?

Answer 2

Transfer energy

Question 3

What are transverse waves?

Answer 3

Waves where the oscillations are perpendicular to the direction of energy transfer (e.g. electromagnetic waves, water waves). Not all transverse waves require a medium

Question 4

What equation links period (time taken for a wave to be produced) to wavelength?

Answer 4

P = 1/f
P = period (s)
f = Frequency (Hz)

Question 5

What equation links wave speed to frequency and wavelength?

Answer 5

V = fλ
V = Speed (m/s)
f = Frequency (Hz)
λ = Wavelength (m)

Question 6

What are longitudinal waves?

Answer 6

Waves where the oscillations are parallel to the direction of energy transfer (e.g. sound waves). These waves all require a medium such as air

Question 7

What is special about transverse waves?

Answer 7

It’s the wave that moves and not the medium

Question 8

How would you measure the speed of sound?

Answer 8

1. Get a stopwatch
2. Stand 500 metres away from someone with 2 cymbals
3. Start timing when you see the person smash the cymbals together
4. Stop timing when you hear the sound
5. Calculate a mean and use s=d/t to calculate the speed of sound

Question 9

What is a wave’s frequency?

Answer 9

Number of waves passing a point per second

Question 10

How are electromagnetic waves produced?

Answer 10

When atoms are heated, electrons move from outer shells to inner shells (higher energy levels). When electrons return to their original shells, electromagnetic waves (e.g. light) are produced. Alternatively, unstable nuclei can release energy in the form of electromagnetic waves (gamma waves)

Question 11

What are some of the dangers of electromagnetic waves?

Answer 11

When absorbed, high frequency electromagnetic waves can knock electrons off atoms, causing chemical changes which can lead to DNA mutations and cancer

Question 12

How are radio waves transmitted and received?

Answer 12

Radio waves are produced when electrons oscillate in AC electrical circuits. The opposite process takes place in receivers

Question 13

What is the electromagnetic spectrum?

Answer 13

From low to high wavelength: Radio waves, Microwaves, Infrared, Visible, Ultraviolet, X-ray, Gamma ray

Question 14

What are the uses of radio waves?

Answer 14

Transmitting radio and terrestrial TV signals (they can spread out easily and travel long distances before being absorbed). We can also send radio waves very long distances around earth, due to the fact that they reflect off the ionosphere

Question 15

What are the uses of microwaves?

Answer 15

Heating up food (water molecules in the food absorb the energy of the waves and heat up, causing the temperature of the food to increase). They are also used to communicate with satellites in space (they can pass through the atmosphere without being reflected or refracted)

Question 16

What are the uses of infrared?

Answer 16

Emitted by electrical heaters, used to cook food in ovens (infrared radiation energy is easily absorbed by the surface of objects). Infrared is also used in infrared cameras to detect heat losses from buildings

Question 17

What are the uses of visible light?

Answer 17

Fibre-optics (used to transmit pulses of light down cables). Due to the short wavelength of visible light it can transmit a high amount of information

Question 18

What are the uses of ultraviolet?

Answer 18

Energy-efficient light bulbs (UV is higher energy than visible). The energy of the UV is captured by the internal surface of the bulb and converted into visible light. This requires less energy than a normal light bulb. UV is also used for tanning (can increase cancer risk)

Question 19

What are X-rays and gamma rays used for?

Answer 19

X-rays are used to scan for broken bones, and gamma rays are used to check for cancer. They are both very penetrating, but X-rays can be absorbed by bones. They are both also used to treat cancer

Question 20

What is refraction?

Answer 20

Where light appears to change direction when passing through water or another medium. Waves can change direction when they change speed

Question 21

What happens when waves slow down when entering another medium?

Answer 21

They bend towards the normal (line perpendicular to the medium). The opposite occurs when waves speed up. This causes the image of the object to change position