Waves

Question 1

What is a wave?

Answer 1

A transfer of energy from one place to another without the transfer of matter

Question 2

What is the substance that a wave passes through called?

Answer 2

The medium

Question 3

What is the equilibrium position?

Answer 3

Where the particle is found when no energy is passing through

Question 4

What are the two types of waves?

Answer 4

Transverse and longitudinal

Question 5

How do particles in the medium of a transverse wave vibrate?

Answer 5

Perpendicular (at right angles) to the direction of energy. (If the energy is going to the left, the particles go up and down)

Question 6

What is the top end position of a particle’s vibration? (transverse)

Answer 6

Crest

Question 7

What is the bottom end position of a particle’s vibration? (transverse)

Answer 7

Trough

Question 8

Examples of transverse waves

Answer 8

Light waves and earthquake S waves

Question 9

How do particles in the medium of a longitudinal wave vibrate?

Answer 9

Parallel to the direction of the energy transfer.

Question 10

What is it called when the particles of a longitudinal wave are close together?

Answer 10

Compression

Question 11

What is it called when the particles of a longitudinal wave are spread apart?

Answer 11

Rarefaction.

Question 12

Examples of longitudinal waves

Answer 12

Sound waves, earthquake P waves

Question 13

Amplitude

Answer 13

The maximum displacement of a particle in the medium from its equilibrium position. The more energy (louder, brighter), the large the wave amplitude. Measured in meters (m), symbol (A)

Question 14

Wavelength

Answer 14

The distance between two successive particles undergoing the same motion. Ie distance from a trough to a trough, or rarefaction to a rarefaction. Measured in meters (m), symbol λ

Question 15

Period (T)

Answer 15

The time taken for one complete wave to pass a point. Ie - the time for two crests to pass by. Measured in seconds (s), symbol (T)

Question 16

Frequency (f)

Answer 16

The number of complete waves passing a point per second. Measured in hertz (Hz). Symbol (f). Higher frequency, higher pitch. Different colours have different frequencies.

Question 17

Echo

Answer 17

When sound waves are reflected and bounced back, we hear the reflected sound as an echo.

Question 18

Reflection

Answer 18

When waves hit a surface and bounce off

Question 19

Ray

Answer 19

A ray is an arrow drawn that represents the direction in which energy is being transferred by a wave

Question 20

What two things happen when a wave hits a different medium?

Answer 20

Some of the energy is reflected off the surface, some of the energy enters the new medium

Question 21

When a wave is reflected, what changes?

Answer 21

The amplitude will decrease as some energy will be transferred to the medium

Question 22

What is the ray called that goes into the other medium?

Answer 22

Incident ray (with the angle of incidence)

Question 23

What is the ray called that goes out of the other medium?

Answer 23

The reflected ray (with the angle of reflection)

Question 24

Refraction

Answer 24

The change in speed of a wave when a wave travels from one medium to another

Question 25

Refractive index symbol

Answer 25

n, no units

Question 26

If a wave is slowing down when entering a new medium, it will bend ...

Answer 26

Towards the normal

Question 27

If a wave is speeding up when entering the new medium, it will bend ...

Answer 27

Away from the normal

Question 28

What does the speed of light depend on in a transparent medium?

Answer 28

The optical density

Question 29

What is the refractive index?

Answer 29

The measure of the speed a wave will travel in a medium. The higher n, the slower the wave will travel

Question 30

Refractive Index units

Answer 30

No units but symbol n

Question 31

What do we see as a wave?

Answer 31

The vibration of the particles in the medium

Question 32

Where is the normal?

Answer 32

90 degrees from the surface

Question 33

What is the law of reflection?

Answer 33

That the angle of incidence and the angle of reflection are the same

Question 34

What direction does a wave reflect on a smooth even surface and a uneven surface?

Answer 34

Smooth surface - regular reflection, parallel rays Rough surface - diffuse reflection - all at different directions

Question 35

What is a plane mirror?

Answer 35

A flat mirror

Question 36

What happens when light is reflected off a plane mirror?

Answer 36

An image of the original object will be formed in the mirror

Question 37

Images in plane mirrors are what distance, size etc

Answer 37

Laterally inverted, same size, same distance behind the mirror as the object is in front of the mirror, virtual

Question 38

What is the refractive index of light in the air?

Answer 38

n = 1.00

Question 39

Snell's law is used to find the refractive index (n) of a medium. When is it used?

Answer 39

When light is travelling from air into another medium.

Question 40

Why does an object under water appear shallower than it actually is?

Answer 40

Our brain thinks that light waves travel in straight line. The refraction of the ray due to the change in medium. Our brain follows the refraction ray into the new medium so the lines meet at a shallower depth and the coin appears closer.

Question 41

What is a wavefront?

Answer 41

A line drawn to represent the part of a wave where the medium is undergoing the same motion (crests or compressions etc).

Question 42

What is the distance between wavefronts?

Answer 42

The wavelength

Question 43

When would a wavefront not be straight lines?

Answer 43

When a stone is dropped in water.- if the wave speed is the same in all directions, circular wavefronts will be formed

Question 44

When a wavefront is refracted, where do you draw the wavefronts?

Answer 44

At 90 degrees to the refracted ray

Question 45

When a wave slows down (wavefront), what changes/stays the same?

Answer 45

Wave speed decreases, frequency stays the same so wavelength decreases

Question 46

What is total internal reflection?

Answer 46

Where light becomes trapped within a medium, occurs when light is travelling from a more to less optically dense medium. The angle of incidence is greater than the critical angle.

Question 47

What happens when the angle of incidence is equal to the critical angle?

Answer 47

The light travels along the medium.

Question 48

The lower the refractive index...

Answer 48

The lower the number on the index, the faster light travels through the medium, the less the light is bent

Question 49

Diffraction

Answer 49

When waves move past an object or gap and tend to spread out

Question 50

When are circular wavefronts created in diffraction?

Answer 50

When the gap is approximately equal to the wavelengths

Question 51

Can a sound/light wave travel without a medium?

Answer 51

Light waves can travel through a vacuum but sound waves need a medium.

Question 52

What is dispersion?

Answer 52

When white light enters a prism, a rainbow comes out on the other side. White light is made up of different colours of light in the rainbow with different wavelengths. When they enter the prism, shorter wavelengths slow down more and so refract at the greatest angle, longer wavelengths speed up so refract at a smaller angle. The differing refraction separates them into a spectrum (rainbow). (splitting up of white light into separate colours)

Question 53

How do rainbows occur in the sky?

Answer 53

Water droplets act as tiny prisms, light stays constant so rainbow stays constant

Question 54

Why does a red shirt appear red?

Answer 54

It absorbs all colours but reflects red

Question 55

White light absorbs or reflects light?

Answer 55

White light reflects all light

Question 56

Blacklight absorbs or reflects light?

Answer 56

Blacklight absorbs all light

Question 57

What are the primary colours of light?

Answer 57

Red, green, blue

Question 58

What is a mechanical wave?

Answer 58

A wave that needs a medium for energy to travel through. Eg sound, seismic earthquake waves.

Question 59

What is an electromagnetic wave?

Answer 59

A wave that doesn't need a medium for energy to travel. They can still travel through a medium, however. Eg visible light, radio waves

Question 60

All electromagnetic waves are what?

Answer 60

Transverse waves, can travel through a vacuum, travel at 3 x 10^8.

Question 61

What is the critical angle?

Answer 61

The smallest angle of incidence at which total internal reflection happens.

Question 62

Optical density

Answer 62

Optical density is a measure of how fast light can travel through a substance. The higher the optical density, the slower the wave