3. Waves Definitions

Question 1

Define amplitude

Answer 1

A wave’s maximum displacement from its equilibrium position

Question 2

Define antinode

Answer 2

A position of maximum displacement in a stationary wave

Question 3

Define 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

Define 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

Define 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

Define diffraction

Answer 6

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

Question 7

Define electromagnetic waves

Answer 7

Waves that consist of perpendicular electric and magnetic oscillations

Question 8

Define 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

Define fringe spacing

Answer 9

The distance between adjacent bright fringes or two adjacent dark fringes

Question 10

Define interference

Answer 10

The name given to the superposition of the 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

Define laser

Answer 11

A light source that produces a collimated and coherent beam

Question 12

Define 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

Define 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

Define modal dispersion

Answer 14

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

Question 15

Define node

Answer 15

A position of minimum displacement in a stationary wave

Question 16

Define optical fibre

Answer 16

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

Question 17

Define 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

Define phase difference

Answer 18

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

Question 19

Define phase

Answer 19

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

Question 20

Define 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

Define pulse broadening

Answer 21

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

Question 22

Define 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

Define 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

Define speed of a wave

Answer 24

The product of a wave’s frequency and wavelength

Question 25

Define stationary wave

Answer 25

A wave that stores, but does not transfer, energy

Question 26

Define 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

Define 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

Define 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

Define Young’s Double-Slit experiment.

Answer 29

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