Waves

Question 1

What is the phase difference between between two points on a wave?

Answer 1

It’s the difference in their positions in the wave’s cycles

Question 2

Describe the phase difference between two waves

Answer 2

It’s how much one lags behind the other

Question 3

Describe stationary waves

Answer 3

All points between consecutive nodes are vibrating in phase as they all reach their maximum displacement at the same time

Question 4

What is superposition?

Answer 4

When similar waves meet the total displacement of the wave is the vector sum of the individual displacements

Question 5

What is the first harmonic?

Answer 5

The lowest frequency at which a standing wave is formed, it has an antinode in the centre. It has 1/2 a wavelength

Question 6

What happens when you blow into a pipe like a flute?

Answer 6

A stationary wave is formed in the pipe with nodes at the closed ends and antinodes at the open ends.

Question 7

What is a polarised wave?

Answer 7

A transverse wave whose oscillations are confined to one plane

Question 8

Name two uses of polarising filters

Answer 8

Sunglasses to reduce glare
TV signals, the alignment of the receiving aerial must match the polarisation direction of the transmitted waves

Question 9

When is diffraction most noticeable?

Answer 9

When the aperture is a similar size to the wavelength of the wave

Question 10

Describe the diffraction pattern from a single slit

Answer 10

There is a central maxima which is twice as wide and much more intense than the other maxima. The smaller the gap, the wider the central maxima.

Question 11

What happens when white light passes through the slit?

Answer 11

Each colour diffracts a different amount which leads to a rainbow effect in all but the central maximum

Question 12

What does it mean if two waves are coherent

Answer 12

Two sources of waves are coherent if they have the same frequency, are polarised in the same plane and they maintain a constant phase difference

Question 13

When does constructive interference occur?

Answer 13

When the path difference from the source is a integer number of wavelengths

Question 14

When do you get destructive interference?

Answer 14

When the path difference is a half number of wavelengths (n+0.5) wavelengths

Question 15

Define w=λD/s

Answer 15

Fringe spacing=wavelength×distance between slits and screen/spacing between slits

Question 16

Define dsinx=nλ

Answer 16

Distance between slits×sin(angle between incident beam and nth maximum)=order of maximum×wavelength
d=1/number of slits in 1m

Question 17

What are the two layers of optical fibres?

Answer 17

The inner layer, the core, where the light is transmitted and the outer layer, the cladding, which protects the cable

Question 18

How does light pass through the fibre?

Answer 18

Total internal reflection

Question 19

What is the critical angle?

Answer 19

The angle of incidence at which the light is refracted along the boundary

Question 20

What is snell’s law

Answer 20

n1sinx1=n2sinx2

Question 21

Critical angle equation?

Answer 21

Sinxc=n2/n1

Question 22

What are 4 problems that can occur with optical fibres?

Answer 22

Absorption, some of the signals energy is absorbed by the material of the fibre which reduced the signal amplitude
If a fibre is bent too sharply, the angle the ray makes with the normal will be altered and the light can strike the cladding at less than the critical angle and leave the fibre
Modal dispersion, rays enter at different angles so they take different times to leave the fibre, use a narrower fibre
Chromatic dispersion, white light splits into a spectrum, use monochromatic light