Waves

Question 1

Wave speed

Answer 1

speed = frequency x wavelength
c = fλ

Question 2

Period

Answer 2

f = 1/T

Question 3

First Harmonic

Answer 3

f = 1/2L x sqrt T/μ

Question 4

Fringe spacing

Answer 4

w = λD/s

Question 5

Diffraction grating

Answer 5

d sinθ = nλ

Question 6

Law of refraction (snells law)

Answer 6

N₁ sinθ₁ = N₂ sinθ₂

Question 7

Critical angle

Answer 7

sinθ꜀ = N₂/N₁ as long as N₁ > N₂

Question 8

Define phase difference

Answer 8

How much a waves lags behind another wave

Question 9

What is a progressive wave?

Answer 9

A wave that transfers energy from one place to another without transferring matter

Question 10

What is the equation for phase difference in radians

Answer 10

2πd/λ

Question 11

What is the phase difference between constructive waves

Answer 11

2π

Question 12

What is the phase difference between destructive waves

Answer 12

π

Question 13

What is a longitudinal wave?

Answer 13

A wave where oscillation of the particles is parallel to the direction of the wave

Question 14

What is a transverse wave?

Answer 14

A wave where the oscillation of the particles is perpendicular to the direction of the wave

Question 15

What is plane polarisation?

Answer 15

A method of allowing only transverse waves orientated in the same direction

Question 16

What is a standing wave?

Answer 16

A wave that is the result of the superposition of two waves with the same amplitude, frequency and speed travelling in opposite directions

Question 17

Define the principle of superposition

Answer 17

When two or more coherent waves meet, the total displacement at a point is the sum of displacements of each wave at that point. Waves superpose upon each other by interfering and either produce constructive or destructive interference

Question 18

Define total internal reflection

Answer 18

When a ray of light reaches a boundary with a medium that ahs a lower refractive index and is completely reflected. The angle of incidence is greater than the critical angle

Question 19

Define the term refractive index

Answer 19

The ratio of the velocity of light in a vacuum to its velocity in a medium

Question 20

Define absorption (optical fibres)

Answer 20

Where part of the signals energy is absorbed by the fibre which reduces the amplitude of the signal

Question 21

Define modal dispersion

Answer 21

Light rays enter the fibre at different angles and therefore take different paths. The rays take a different amount of time to travel through the fibre

Question 22

Define pulse broadening

Answer 22

When the pulses of light spread out as thy travel which can cause two consecutive pulses to overlap

Question 23

What two conditions are needed for total internal reflection?

Answer 23

The medium has to have a higher RI

The critical angle has to be exceeded