Topic 3: Waves

Question 1

amplitude

Answer 1

A wave’s maximum displacement from its equilibrium position.

Question 2

antinode

Answer 2

A position of maximum displacement in a stationary wave.

Question 3

cladding

Answer 3

A protective layer on an optical fibre to improve the tensile strength of the fibre, prevent scratching and to prevent signal transfer between adjacent fibres.

Question 4

coherence

Answer 4

Waves are coherent if they have the same wavelength and frequency, as well as there being a fixed phase difference between them.

Question 5

diffraction grating

Answer 5

A grating with hundreds of slits per millimetre, that results in sharper interference patterns. They are used to calculate atomic spacing and to analyse elements.

Question 6

diffraction

Answer 6

The spreading of waves as they pass through a gap of a similar magnitude to their wavelength.

Question 7

electromagnetic waves

Answer 7

Waves that consist of perpendicular electric and magnetic oscillations.

Question 8

frequency

Answer 8

The number of waves that pass a point in a unit time period. It is the inverse of the time period.

Question 9

fringe spacing

Answer 9

The distance between two adjacent bright fringes or two adjacent dark fringes.

Question 10

interference

Answer 10

The name given to the superposition of waves that occurs when two waves meet. If the waves are in phase they will constructively interfere, but if they are out of phase, they will destructively interfere.

Question 11

laser

Answer 11

A light source that produces a collimated and coherent beam.

Question 12

longitudinal wave

Answer 12

A wave with oscillations that are parallel to the direction of energy propagation. Sound waves are an example of a longitudinal wave.

Question 13

material dispersion

Answer 13

Waves of different wavelengths travel at slightly different speeds through an optical fibre and so reach the end of the fibre at slightly different times, causing pulse broadening. The use of monochromatic light fixes this.

Question 14

modal dispersion

Answer 14

Waves enter an optical fire at sighity different angles, meaning the distance each beam has to travel is slightly different. This loads to the beams reaching the end at different times and so causes pulse broadening.

Question 15

node

Answer 15

A position of minimum displacement in a stationary wave.

Question 16

optical fibre

Answer 16

A thin glass fibre through which signals are passed through. Optical fibres usually have cladding surrounding them.

Question 17

path difference

Answer 17

A measure of how far ahead a wave is compared to another wave, usually expressed in terms of the wavelength.

Question 18

phase difference

Answer 18

The difference in phase between two points on a wave. It is usually expressed in radians.

Question 19

phase

Answer 19

A measure of how far through the wave’s cycle a given point on the wave

Question 20

polarisation

Answer 20

The restriction of a wave so that it can only oscillate in a single plane. This can only occur for transverse waves.

Question 21

pulse broadening

Answer 21

The elongation of a signal passed down an optical fibre, commonly due to modal or material dispersion.

Question 22

refractive index

Answer 22

A material property that is equal to the ratio between the speed of light in a vacuum, and the speed of light in a given material.

Question 23

snell’s law

Answer 23

A law linking a wave’s angle of incidence to its angle of refraction, with the use of the refractive indexes of the mediums involved.

Question 24

speed

Answer 24

The product of a wave’s frequency and wavelength.

Question 25

stationary wave

Answer 25

A wave that stores, but does not transfer, energy.
2 stationary waves
same frequency, wavelength, amplitude
superposition to 0 displacement

Question 26

total internal reflection

Answer 26

An effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, meaning no radiation passes out.

Question 27

transverse wave

Answer 27

A wave with oscillations that are perpendicular to the direction of energy propagation. Electromagnetic waves are examples of transverse waves.

Question 28

wavelength

Answer 28

The distance between two identical positions on two adjacent waves. It is commonly measured from peak to peak or trough to trough.

Question 29

Young’s double slit experiment

Answer 29

An experiment that demonstrates the diraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of bright and dark fringes.