waves

Question 1

define a progressive wave

Answer 1

an oscillation of particles/fields in a medium that transfers energy from one point to another, without transferring material

Question 2

give an equation for wave speed

Answer 2

c=fλ

Question 3

give an equation for frequency, with relation to period.

Answer 3

f= 1/T

Question 4

define a transverse wave

Answer 4

the direction of oscillation is perpendicular to the direction of motion of the energy. i.e. electromagnetic

Question 5

what is a longitudinal wave

Answer 5

the direction of the oscillation is parallel to the direction of motion of the energy i.e. sound waves

Question 6

define polarization, and give an application

Answer 6

only allowing a wave to oscillate on one plane,

van be used in sunglasses/aerials

Question 7

state the equation for the law of reflection

Answer 7

θ1=θ2

Question 8

state the equation for refractive index

Answer 8

n =c/c(s)

where c is the speed of light and c(s) is the speed of light in the material

Question 9

give snell’s law of refraction

Answer 9

n(a)sinθ(a) = n(b)sinθ(b)

Question 10

what properties are affected by refraction

Answer 10

wavelength varies, wave speed varies

Question 11

what is the refractive index of air

Answer 11

1

Question 12

what is total internal reflection

Answer 12

where no refraction occurs if the angle of incidence is greater than the critical angle
sinθ =n(b)/n(a)

Question 13

describe step index optical fibres, and the use of their cladding

Answer 13

• thin glass fibres that fire signals made of light pulses
• light undergoes TIR, so no light escapes
• cladding has a lower refractive index to ensure TIR happens
• cladding acts as protection for thin fibre

Question 14

what is modal dispersion?

Answer 14

when light rays enter a fibre at different angles causing them to take longer to reach the end.

Question 15

what is material dispersion, and how do you prevent it?

Answer 15

when different wavelengths travel at different speeds resulting in them arriving at different times
(can be overcome by using monochromatic light)

Question 16

what is diffraction

Answer 16

waves spreading out after passing through a gap with a similar size to the wavelength

Question 17

Define monochromatic

Answer 17

Single wavelength

Question 18

Define coherent

Answer 18

Constant phase difference

Question 19

State a safety precaution when using a laser

Answer 19

dont look into the laser

Question 20

State and explain the effect of using a laser with a shorter wavelength on the maxima spacing in Young’s double slit

Answer 20

Maxima closer together

use w=𝜆D/s

Question 21

Use wave theory to explain how the fringe pattern is formed

Answer 21

Slits act as coherent sources
Waves diffract at slits
Waves superpose
Bright patches: constructive
Dark patches: destructive

Question 22

State two requirements for two light sources to be coherent

Answer 22

Same wavelength

Same phase

Question 23

Explain how Young’s double slit arrangement produces interference fringes, refer to width of first slit and coherence of second slits

Answer 23

Narrow single slit gives wide diffraction to ensure that both second slits are illuminated
Paths to second slits are of constant length giving constant phase difference
Light diffracted at slits and overlap and interfere
Where path lengths differ by whole number of wavelengths, constructive interference occurs producing a bright fringe

Question 24

If Young’s double slit was carried out with red light and then with white light, how would the two differ?

Answer 24

Central fringe would be white
Dark fringes would be closer together
Side fringes are spectra

Question 25

State two ways a diffraction pattern on single slit would change if the slit became narrower

Answer 25

Increased separation

Lower intensity

Question 26

State and explain what happens to angle θ in λ = d sin θ when wavelength decreases?

Answer 26

Angle θ gets smaller

As path difference gets smaller

Question 27

Why will total internal reflection occur when light ray travels from water into glass?

Answer 27

TIR only occurs when ray travels from higher n to lower n

Question 28

State and explain an advantage of a smaller diameter core in a fibre optic

Answer 28

Reduce multipath

Which would cause poor resolution

Question 29

Define amplitude of a wave

Answer 29

The maximum displacement of the wave from the equilibrium position

Question 30

What is an S-wave?

Answer 30

A secondary wave that is transverse

Question 31

What is a P-wave?

Answer 31

A primary wave that is longitudinal

Question 32

What is a compression and a rarefaction?

Answer 32

A compression is an area of high pressure and a rarefaction is an area of low pressure

Question 33

What is the principle of superposition?

Answer 33

This is when two waves overlap, they superpose. When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves.