Chapter 8 - Waves

Question 1

What is a longitudinal wave ?

Answer 1

A longitudinal wave is one in which the particles vibrate parallel to the direction in which the wave is travelling

Question 2

Name 4 types of longitudinal waves

Answer 2

• sound waves
• ultrasound waves
• slinky spring waves
• p-type earthquake waves

Question 3

What are compressions ?

Answer 3

A place where the particles bunch together

Question 4

What are rarefactions ?

Answer 4

Are places where the particles are furthest apart

Question 5

What is a transverse wave ?

Answer 5

A transverse wave is one in which the vibrations are at 90*

Question 6

Give some examples of transverse waves

Answer 6

• water waves
• waves on strings and ropes
• electromagnetic waves

Question 7

Name 3 ways how you can prove that waves carry energy

Answer 7

• water waves can be used to generate electricity
• loud sound waves can cause things to vibrate
• microwaves make things heat up

Question 8

What is the frequency of a wave ?

Answer 8

The frequency of a wave is the number of complete waves passing a fixed point in a second

Question 9

What are the units for frequency ?

Answer 9

Hz (hertz)

Question 10

What is the wavelength ?

Answer 10

The wavelength of a wave is the distance between two consecutive crests or troughs

Question 11

What is wavelength measured in ?

Answer 11

measured in meters and the symbol is ‘landa’

Question 12

What is the amplitude of a wave ?

Answer 12

The amplitude of a wave is the greatest displacement of the wave from its undisturbed position

Question 13

What is the unit of amplitude ?

Answer 13

meters, m

Question 14

How do you find the wavelength in a longitudinal wave ?

Answer 14

It is found by measuring the distance from one compression to the next

Question 15

What is the equation for wave speed ?

Answer 15

wave speed = frequency x wavelength

Question 16

What properties does a wave reflected off a barrier have ?

Answer 16

• the angle of incidence = the angle of reflection
• the wavelengths are equal
• the frequencies are equal
• there is continuity of incident waves and reflected waves at the barrier

Question 17

How does changing the depth of the water change how quickly waves can travel through it ?

Answer 17

Waves can travel more slowly through shallower water

the frequency of water travelling through shallow and deep water are equal, so the shallower water must have a shorter wavelength

Question 18

What should be noted when water travels through deep water ?

Answer 18

• angle of incidence in deep water is always bigger than the refraction of shallow water
• wavelength and speed of waves in deep water are greater
• frequencies are the same
• there is continuity of incident and refracted waves at the boundary

Question 19

What is the analogy between water and light waves?

Answer 19

True for both water wavs and light

• angle of incidence = angle of reflection
• reflected wavelength = incident wavelength
• reflected frequency = incident frequency
• reflected speed = incident speed
• the refracted wavelength is less than the incident one
• the refracted speed is less than the incident speed

Question 20

What is the range of audible sound ranges

Answer 20

2Hz to 20000Hz

Question 21

What is sound above 20000Hz called ?

Answer 21

ultrasound

Question 22

Name three ways how humans use ultrasounds

Answer 22

• scanning soft tissues to diagnose cancers
• locating fish by seagoing trawlers
• mapping the surface of the ocean floor

Question 23

Explain an application of ultrasound in medicine

Answer 23

• the probe sends out ultrasound rays and records reflections
• ultrasound can be sent out in a very narrow beam
• by examining the reflections the computer builds up a picture of the foetus

Question 24

How is ultrasound used in scanning metal castings ?

Answer 24

• special devices fitted to a railway track
• ultrasound passes through the track
• if there is a crack or flaw it can be imaged by a computer

Question 25

How quickly does ultrasound travel in steel ?

Answer 25

5000 m/s

Question 26

What does sonar stand for ?

Answer 26

Sound navigation and ranging

Question 27

How quickly does ultrasound travel in seawater ?

Answer 27

1500 m/s

Question 28

What does radar stand for ?

Answer 28

Radio detection and ranging

Question 29

What are some uses for radar ?

Answer 29

• tracking planes
• tracking missiles
• detect ships

Question 30

Why is radar used ?

Answer 30

It travels very fast and can be used to track things that move very quickly

Question 31

Can radar be used underwater ?

Answer 31

No

Question 32

What can electromagnetic waves do ?

Answer 32

• can travel in a vacuum
• all travel at exactly the same speed in a vacuum
• are transverse waves

Question 33

Give three examples of electromagnetic waves

Answer 33

• X-rays
• radio waves
• visible light

Question 34

What are the dangers of electromagnetic waves ?

Answer 34

Can disrupt DNA which may lead to cancer:

• gamma rays
• X-rays
• uv light

Cause damage to eye cells
- Visible light

Felt as heat and can cause burns :
- infrared rays