3.3 - DEFINITIONS

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

Question 4

coherent waves

Answer 4

waves which have the same wavelength and frequency and a fixed phase difference

Question 5

diffraction grating

Answer 5

a grating with hundreds of slits per millimetre which results in sharper interference patterns

Question 6

diffraction

Answer 6

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

Question 7

electromagnetic waves

Answer 7

waves which 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

Question 9

fringe spacing

Answer 9

the distance between two adjacent bright fringes or two adjacent dark fringes

Question 10

interference

Answer 10

the superposition of waves which occurs when two waves meet; either constructive or destructive

Question 11

laser

Answer 11

a coherent light source

Question 12

longitudinal wave

Answer 12

a wave with oscillations that are parallel to the direction of energy propagation

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

Question 14

modal dispersion

Answer 14

waves enter an optical fibre at slightly different angles, so the distance each beam has to travel is slightly different; this leads to 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 with a surrounding layer of cladding through which signals are passed

Question 17

path difference

Answer 17

a measure of how far ahead a wave is compared to another wave; terms of the wavelength

Question 18

phase difference

Answer 18

the difference in phase between two points on a wave; radians

Question 19

Phase

Answer 19

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

Question 20

polarisation

Answer 20

the restriction of a wave so that it can only oscillate in a single plane; only for transverse waves

Question 21

pulse broadening

Answer 21

the elongation of a signal passed down an optical fibre, due to modal/material dispersion

Question 22

refractive index

Answer 22

a material property; the ratio of speed of light in a vacuum to the speed of light in a given material

Question 23

stationary wave

Answer 23

a wave that stores, but does not transfer, energy

Question 24

total internal reflection

Answer 24

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

Question 25

transverse wave

Answer 25

a wave with oscillations that are perpendicular to the direction of energy propagation