Module 4 - Chapter 11 - Waves 1

Question 1

What is a progressive wave?

Answer 1

A progressive wave is an oscillation that travels through matter to transfer energy from one place to another.

Question 2

What is a transverse wave?

Answer 2

A transverse wave is a progressive wave where the oscillations are perpendicular to the direction of energy transfer.

Question 3

Give 3 examples of transverse waves

Answer 3

Water waves
Electromagnetic waves
S-waves

Question 4

What is a longitudinal wave?

Answer 4

A longitudinal wave is a progressive wave where the oscillations are parallel to the direction of energy transfer.

Question 5

What is the displacement of a wave?

Answer 5

The displacement is the distance from the equilibrium. (m)

Question 6

What is the amplitude of a wave?

Answer 6

The amplitude is the maximum distance a wave goes from equilibrium. (m)

Question 7

What is the wavelength?

Answer 7

The wavelength is the distance between 2 point on the wave that are in phase with each other. (m)

Question 8

What is the period of oscillation / time period?

Answer 8

The period of oscillation or the time period is the time it takes for one full oscillation to complete. (s)

Question 9

What is the frequency?

Answer 9

The frequency is the number of wavelengths passing past a point every second. (Hz)

Question 10

What is the wave speed?

Answer 10

The wave speed is the distance travelled by the wave per second. (m/s)

Question 11

State the wave equation

Answer 11

v = fλ
wave speed (m/s) = frequency (Hz) x wavelength (m)

Question 12

State the time period equation

Answer 12

f = 1/T
T = 1/f
time period = 1 / frequency

Question 13

What is phase difference?

Answer 13

Phase difference is the difference in displacement of particles in a wave or waves.

Question 14

What is phase difference measured in and what is 1 complete cycle equivalent to in this unit?

Answer 14

Phase difference is measured in ° or radians, 1 full cycle is 2π radians or 360°.

Question 15

What is antiphase?

Answer 15

Antiphase is when the 2 points have a phase difference of 180° or π radians this means that the waves are out of phase by 1/2 of a wavelength so they would oscillate in complete opposite directions to each other.

Question 16

What is the law of reflection?

Answer 16

The law of reflection states that the angle of incidence is equal to the angle of reflection.

Question 17

What is refraction?

Answer 17

Refraction is when the wave changes direction from going from one medium to another with different densities.

Question 18

What is diffraction?

Answer 18

Diffraction is when waves pass through a gap or past a corner they spread out.

Question 19

What is polarisation?

Answer 19

Polarisation means that the wave only oscillates on one plane / in one direction. Only transverse waves can be polarised.

Question 20

What is intensity?

Answer 20

The intensity of a progressive wave is the radiant power passing through a surface area per unit area.

Question 21

State the equation for intensity

Answer 21

I = P/A
intensity = radiant power / surface area

Question 22

What is special about EM waves?

Answer 22

They can travel through a vacuum.

Question 23

How can you write the wave equation differently for EM waves?

Answer 23

since EM waves travel 3 x 10⁸ m/s in a vacuum and a very similar speed in air, we can use c to represent this and write the equation different
c = fλ

Question 24

What is a polariser?

Answer 24

A polariser is a filter that only lets waves through in one way because of its fence like structure.

Question 25

What is the refractive index?

Answer 25

The refractive index is to do with the material of a medium that makes light refract differently depending on the refractive index even if the angle the light is approaching the medium does not change.

Question 26

State the equation to find the refractive index

Answer 26

n = c / v refractive index = speed of light through vacuum / speed of light through material n₁sinθ₁ = n₂sinθ₂

Question 27

What is needed for total internal reflection?

Answer 27

1. The light must be in a medium with a higher refractive index at a boundary than the other medium at the boundary. 2. The light must hit the boundary at an angle greater than the critical angle from the normal. This angle depends on the refractive index of the material.

Question 28

What is the relationship between the critical angle and the refractive index?

Answer 28

sinC = 1 / n sin(critical angle) = 1 / refractive index From this we can see that if the refractive index is bigger, the critical angle will be smaller, also making it easier for TIR to be achieved.