4.4 Waves

Question 1

What is a progressive wave?

Answer 1

An oscillation that travels through matter (or in some cases a vacuum), transferring energy from one place to another, but not transferring any matter.

Question 2

What is a transverse wave? Give an example.

Answer 2

A wave with oscillations that are perpendicular to the
direction of energy transfer.

For example, EM waves.

Question 3

What is a longitudinal wave? Give an example.

Answer 3

A wave with oscillations that are parallel to the direction of energy transfer. They cannot travel through a vacuum.

For example, sound waves.

Question 4

Define displacement.

Answer 4

The distance from the equilibrium position in a particular direction.

Question 5

Define amplitude.

Answer 5

The maximum displacement from the origin.

Question 6

Define wavelength.

Answer 6

The minimum distance between two adjacent points on a wave oscillating in phase.

Question 7

Define period.

Answer 7

The time taken for a full oscillation of one wavelength to pass a given point

Question 8

Define frequency.

Answer 8

The number of complete oscillations passing a given point per unit time.

Question 9

How can we find the frequency of a wave?

Answer 9

Frequency (f) = 1 / Period (T)

Question 10

What are two equations for finding wave speed?

Answer 10

Wave speed (v) = Wavelength (λ) / Period (T)

Wave speed (v) = Wavelength (λ) x Frequency (f)

Question 11

Define reflection

Answer 11

When waves rebound from a barrier, changing direction but remaining in the same medium.

Question 12

How does light reflecting off a mirror work?

Answer 12

The angle of the incident ray to the normal of the boundary between the two media is the same as the angle of the reflected ray to the normal.

Question 13

How does wavelength and frequency change during reflection?

Answer 13

It doesn’t.

Question 14

Define refraction.

Answer 14

When waves change direction when they travel from one medium to another due to a difference in the wave speed in each medium.

Question 15

A wave has been refracted.

How has the frequency of the refracted wave changed in the new medium?

Answer 15

It is the same.

Question 16

A wave has been refracted.

How has the speed of the refracted wave changed in the new medium?

Answer 16

It has changed, depending on the type of wave and the density of material.

Sound waves speed up in denser materials, whereas EM waves slow down.

The wavelength changes, as a result.

Question 17

A sound wave is refracted in a dense material.

How has its speed changed?

Answer 17

It has sped up.

Question 18

An EM wave is refracted in a dense material.

How has its speed changed?

Answer 18

It has slowed down.

Question 19

In refraction, wave speed changes whereas frequency remains the same. How does this affect wavelength?

Answer 19

Wavelength also changes.

Question 20

What will there always be in refraction?

Answer 20

Partial reflection at the boundary between the two media.

Question 21

What is diffraction?

Answer 21

The spreading out of a wave front as it passes through a gap.

Question 22

How is wavelength and frequency affected during diffraction?

Answer 22

They remain the same.

Question 23

When will maximum diffraction occur?

Answer 23

When the gap the wave passes through is the same size as the wavelength of the incident wave.

Question 24

Polarisation is a property unique to what kind of wave?

Answer 24

Transverse waves.

Question 25

When does polarisation occur?

Answer 25

When the oscillation of a wave is restricted to one place only - this type of wave is said to be plane polarised.

Question 26

Why can longitudinal waves not experience polarization?

Answer 26

The direction of energy transfer is already in one plane only.

Question 27

Why can transverse waves experience polarization?

Answer 27

The oscillations occur in many planes, at right angles to the direction of travel.