Waves

Question 1

What can we use waves for?

Answer 1

Transmitting energy and information

Question 2

What is the direction of travel of the wave the same as?

Answer 2

The direction in which the wave transfers energy

Question 3

Describe a transverse wave

Answer 3

The oscillation (vibration) of the particles is perpendicular to the direction in which the wave travels

Question 4

Describe a lonitudinal wave

Answer 4

The oscillation of the particles is parallel to the direction of the wave

Question 5

Describe electromagnetic waves

Answer 5

• Can travel through a vacuum
• There are no particles moving, they are oscillations in electric and magnetic fields
• Are transverse

Question 6

Describe mechanical waves

Answer 6

• E.g. waves on springs and sound waves
• Travel through a medium (substance)
• Can be transverse or longitudinal

Question 7

Describe sound waves

Answer 7

• Vibrations in the air/other media
• These are eventually picked up by your ear, producing the sound
• Longitundial

Question 8

Aside from transverse and longitundal, what types of waves are there (and are they transverse or longitundinal)?

Answer 8

• Electromagnetic - Transverse
• Mechanical - Either
• Sound - Longitundinal

Question 9

Do longitudinal waves have an amplitude?

Answer 9

No

Question 10

What is the amplitude of a wave?

Answer 10

The height of the wave crest or the depth of the wave trough from the position at rest

Greater amplitude = more energy

Defines the loudness of a sound wave (think of amps)

Question 11

Complete the sentence:

The greater the amplitude of a wave…

Answer 11

…the more energy a wave has

Question 12

What is the wavelength of a wave?

Answer 12

The distance from one crest to the next, or from one trough to the next

Measured in metres

Question 13

What is the frequency of a wave?

Answer 13

The number of complete waves passing a set point per second

Measured in hertz (Hz) which is equivalent to per second

Question 14

What is the wavelength of a longitudinal wave?

Answer 14

The distance from the middle of one compression/rarefaction to the next

(Instead of from one peak/crest/trough)

Question 15

What is the frequency of a longitudianl wave?

Answer 15

The number of compressions passing a point per second

(As opposed to crests/troughs/peaks. Still complete waves)

Question 16

What is meant by a plane mirror?

Answer 16

A flat mirror

Question 17

When drawing a ray diagram, what should you always remember?

Answer 17

To draw the normal!

Question 18

Where is the normal line drawn?

Answer 18

Perpendicular to the mirror/medium at the point where the incident ray hits the mirror

Question 19

What does the law of reflection state?

Answer 19

That the angle of incidence is equal to the angle of reflection

Question 20

What is the angle of incidence/reflection?

Answer 20

The angle between the incident/reflected ray and the normal

I.e. Not the medium/mirror!

Question 21

Describe the image formed on a mirror

Answer 21

• Same size as the object (not magnified/diminshed)
• Upright
• Same distance behind the mirror as the object is in front
• Virtual

Question 22

What is a real image?

Answer 22

One that can be formed on a screen becayse the rays of light actually pass through it

Question 23

What is a virtual image?

Answer 23

Cannot be formed on a screen because the rays of light only appear to pass through it

Question 24

What changes when a wave crosses a boundary between different substances?

Answer 24

The speed and wavelength

The frequency stays the same

The wave also changes direction due to the change in speed

Question 25

Refraction is a property of what kind of wave?

Answer 25

All kinds

Question 26

What does the change in the speed of a wave cause?

Answer 26

A change in direction (refraction)

Question 27

What happens when light enters a **more dense** substance?

Answer 27

It slows down and bends **towards** the normal

Question 28

What happens when light enters a **less** dense substance?

Answer 28

It speeds up and bends **away** from the normal

Question 29

If light is travelling along the normal and enters a different substance, what will happen?

Answer 29

It will not change direction

Question 30

What is dispersion?

Answer 30

* **Different colours of light have different wavelengths** * These are **refracted by slightly different amounts** when entering a different substance * When a ray of **white light** is shone onto a **triangular prism** we can see this because a **spectrum is produced** * Violet light is refracted the most, red light the least

Question 31

Why does light split up into different colours when it passes through a triangular prism?

Answer 31

Because the different wavelengths of light are refracted by different amounts

Question 32

What types of waves is diffraction a property of?

Answer 32

All waves

Question 33

What is diffraction?

Answer 33

The spreading out of waves when they pass through a gap/around an obstacle It is most noticable if the wavelength of a wave is about the same size as the gap/obstacle

Question 34

Why don't we often observe the diffraction of light during everyday life?

Answer 34

Because the wavelength of light is very short

Question 35

Why might someone get poor TV/mobile signal if they live in a hilly area?

Answer 35

* These signals are carried by radio waves * These might be blocked by a hill * Radio waves will be diffracted around the hill * If they do not diffract enough, the signal will not reach the reciever aerial and will be poor

Question 36

Draw a diagram showing diffraction through a narrow and wide gap

Answer 36

Question 37

What causes sound?

Answer 37

Mechanical vibrations in a substance. It travels as waves

Question 38

What can sound travel through and at what speed (roughly)?

Answer 38

Can travel through solids, liquids, and gases. It travels fastest in solids and slowest in gases *In other words, sound needs a medium through which to travel*

Question 39

What can sound not travel through and how do we know this?

Answer 39

It cannot travel through a vacuum This can be tested by listening to a ringing bell in a 'bell jar'. If the air is pumped out of the jar, the sound fades away.

Question 40

What range of frequencies of sound can be heard by the human ear, and how does age affect this?

Answer 40

20Hx to 20,000Hz The ability to hear higher frequencies declines with age

Question 41

What are the reflections of sound waves called?

Answer 41

Echoes

Question 42

What affects how/if echoes are produced?

Answer 42

* Only **hard, flat surfaces** such as flat walls and floors **reflect** sound * **Soft things** like carpets, curtains, and furniture **absorb** sounds * An empty room will sound different once soft furnishings etc. are put into it/removed

Question 43

Where does the refraction of sound waves take place?

Answer 43

At the boundaries between layers of air at different temperatures

Question 44

What does the pitch of a note/sound depend upon?

Answer 44

The frequency of a wave The higher the frequency, the higher the pitch

Question 45

What does the loudness of a note/sound depend upon?

Answer 45

The amplitude of a wave The higher the amplitude, the louder the sound This is because the wave carries more energy *(Think of amps)*

Question 46

What does an oscilloscope show?

Answer 46

Waves + the differences in **waveform** (comparing waves)

Question 47

What can tuning forks and signal generators be used to produce?

Answer 47

'Pure' waveforms

Question 48

What does the quality of a note depend upon?

Answer 48

The waveform

Question 49

Why do different instruments not sound the same?

Answer 49

Because they produce different waveforms

Question 50

How do musical instruments produce sound?

Answer 50

* **Vibrations** created in an instrument when it is played produce sound waves * In some instruments, e.g. saxophones, a **column of air vibrates** * In others, e.g. a violin, a **string vibrates** * Some instruments **vibrate when they are struck**, e.g. a xylophone