Year 12 - Waves and Optics

Question 1

Amplitude

Answer 1

The maximum displacement of the oscillating particle from the equilibrium/rest position.

Question 2

Anti-node

Answer 2

Points on a stationary wave that oscillate with maximum amplitude. This is due to Construction.

Question 3

Cladding

Answer 3

The Core of a fibre optic is surrounded by a protective cladding
• keeps signals secure (1)
• reduces pulse broadening (1)
• it keeps most light rays in the core due to total internal reflection at boundary (1)
• it prevents scratching/damage of the core (1)

Question 4

CoherentSource

Answer 4

Waves with the same wavelength/frequency and a constant phase relationship [constant phase difference].

Question 5

Compression

Answer 5

A region where particles are close to one another (High pressure).

Question 6

Construction

Answer 6

Two or more waves overlap in such a way that they combine to create a larger wave.

Question 7

Critical Angle

Answer 7

Angle of incidence when the angle of refraction is equal to 90 degrees.

Question 8

Destruction

Answer 8

Two or more waves overlap in such a way that they cancel each other out.

Question 9

Diffraction

Answer 9

The bending or spreading out of waves, when they travel through a small opening or when they pass round a small obstacle.

Question 10

Diffraction Grating

Answer 10

A grating with hundreds (Typically between 300 to 1000) of lines per millimetre, that cause diffraction when lights passes through.

Question 11

EM Waves

Answer 11

Transverse waves composed of perpendicular oscillating electric and magnetic fields. Hence EM or Electromagnetic.

Question 12

Frequency

Answer 12

The number of complete cycles per unit time.

Question 13

Fringe Spacing

Answer 13

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

Question 14

Horizontal Polarisation

Answer 14

Transverse waves that only oscillate in the horizontal plane.

Question 15

Intensity

Answer 15

The rate of transfer of energy (Power) per unit area.

Question 16

Interference

Answer 16

The superposition of two or more coherent waves to produce regions of maxima and minima in space, according to the principle of superposition.

Question 17

Laser

Answer 17

A light source that produces a coherent beam of light. The waves are identical, in phase, with a constant phase relationship.

Question 18

Longitudinal Wave

Answer 18

Particle vibration same as (or parallel to) direction of propagation(or energy transfer).

Question 19

Material Dispersion

Answer 19

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 20

Maxima

Answer 20

Point of maximum constructive interference.

Question 21

Minima

Answer 21

Point of maximum destructive interference.

Question 22

Modal Dispersion

Answer 22

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

Question 23

Monochromatic

Answer 23

Waves of a single wavelength/frequency.

Question 24

Node

Answer 24

Points on a stationary wave of zero amplitude and appear to be fixed. This is due to Destruction.

Question 25

Optical Fibre

Answer 25

A thin glass fibre through which light signals are passed through. The Core of Optical fibres usually has cladding surrounding it.

Question 26

Path Difference

Answer 26

A measure of the difference in distances waves travel, due to taking different paths, usually expressed in terms of the wavelength.

Question 27

Period

Answer 27

Period T is the time for one complete oscillation/cycle.

Question 28

Phase

Answer 28

A measure of how far through the wave’s cycle a given point on the wave is. A whole cycle is 360 degrees or 2p radians.

Question 29

Phase Difference

Answer 29

The difference in phase between two points on a wave. It is usually expressed in radians. The phase difference between two particles or two waves tells us how much a particle (or wave) is in front or behind another particle (or wave).

Question 30

Polarisation

Answer 30

(only) transverse waves can be polarised, (oscillations) restricted to a single plane.

Question 31

Polarised Light

Answer 31

Transverse waves that only oscillate in a single plane.

Question 32

Progressive Wave

Answer 32

Transfers Energy without transferring matter.

Question 33

Pulse Broadening

Answer 33

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

Question 34

Rarefaction

Answer 34

A region where the particles are furthest apart (Low pressure).

Question 35

Refraction

Answer 35

The bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.

Question 36

Refractive Index

Answer 36

The ratio of the speed of light in a vacuum and the speed of light in a substance

Question 37

Relative Refractive Index

Answer 37

The Ratio of the speed of light in substance 1 compared to the speed of light in substance 2 at a boundary. Alternatively the Ratio of the refractive index of substance 2 compared to the refractive index of substance 1 at a boundary.

Question 38

Stationary Wave

Answer 38

A wave which does not transfer energy from one place to another.

Question 39

Stationary Wave Conditions

Answer 39

Superposition of 2 progressive waves, with the same frequency/wavelength and speed, travelling in opposite directions, with a phase difference of 180 degrees.

Question 40

Superposition

Answer 40

When two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point.

Question 41

Total Internal Reflection

Answer 41

Reflection that occurs when light rays travel from a more optically dense medium to a less optically dense medium.

Question 42

Transverse Wave

Answer 42

Particle vibration perpendicular to direction of propagation (or energy transfer).

Question 43

Unpolarised Light

Answer 43

Transverse waves where the wave’s oscillations (or vibrations) exist in more than a single plane.

Question 44

Vertical Polarisation

Answer 44

Transverse waves that only oscillate in the vertical plane.

Question 45

Wave Displacement

Answer 45

Displacement is the distance moved by the particle from its equilibrium/rest position.

Question 46

Wave Speed

Answer 46

The distance travelled by a wave per unit time. Measured in metres per second.

Question 47

Wavelength

Answer 47

The wavelength is the distance between 2 adjacent points on a wave which are in phase with one another.

Question 48

Young's Double Slit Experiment

Answer 48

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

Question 49

Young's Double Slit Experiment: Construction

Answer 49

Caused when the path difference of the 2 waves is an integer number of wavelengths. E.g. Path Diff=nl.

Question 50

Young's Double Slit Experiment: Destruction

Answer 50

Caused when the path difference of the 2 waves is an integer number of half wavelengths. E.g. Path Diff=(l/2+n).