WAVES

Question 1

Describe Transverse Wave

Answer 1

Particles oscillate perpendicular to direction of energy propagation.

Question 2

Describe Longitudinal Wave.

Answer 2

Particles oscillate parallel to direction of energy propagation.

Question 3

Define Amplitude.

Answer 3

Maximum displacement of particle from the equilibrium position.

Question 4

Define Wavelength.

Answer 4

Shortest distance between two points in phase.

Question 5

Define frequency.

Answer 5

Number of oscillations per second (of a particle.)

Question 6

Define Time period.

Answer 6

Time for one complete oscillation.

Question 7

Define a polarised wave.

Answer 7

A polarised wave has only vibrations which oscillate in one plane perpendicular to direction wave is travelling.

Question 8

How do polarising filters work?

Answer 8

Works by only allowing through electrical field oscillations in one plane. This works by absorbing the energy of all other planes.
Polarised light is less intense as less energy transmitted through filter.

Question 9

State some applications for polarisation.

Answer 9

Polarising filters used in sunglasses.
Reflected light is weakly polarised.
Polarising filters in sunglasses can be orientated to remove the reflected polarised light.
This reduces glare.

TV transmitters where the aerial has to be orientated in the same plane as the transmitter to receive the signals.

Question 10

Define Refraction.

Answer 10

Refers to bending of a wave when it changes speed (usually when passing from one material to another with different optical density.)

Question 11

Define the normal.

Answer 11

Line at 90⁰ to the surface.

Question 12

Define angle of incidence.

Answer 12

The angle between light Ray and normal.

Question 13

FAST Acronym

Answer 13

Fast
Away from the normal
Slow
Towards the normal

Question 14

Define Critical Angle.

Answer 14

Angle of incidence that provided Angle of refraction of 90⁰

Question 15

State conditions for Total Internal Reflection.

Answer 15

Angle of incidence greater than critical angle.
Light travelling from material with higher refractive index into material with lower refractive index.

Question 16

Describe how an Optical fibre works.

Answer 16

Thin glass fibre that transmits light or infrared radiation. Trapped inside by TIR. Possible if each reflection has angle of incidence greater than critical angle.
This depends on ratio of refractive index of core and cladding

Question 17

Describe step index optical fibre

Answer 17

Has a central core with uniform refractive index,cladding has different smaller refractive index.
Choosing certain materials for core and cladding limits certain wavelengths which can travel through fibre by TIR.

Question 18

Describe Modal dispersion

Answer 18

Occurs when rays in optical fibre they take slightly different paths.
Rays that take longer paths take longer to travel through fibre which increases pulse duration (pulse broadening.)

Occurs multimode fibres as fibre broad enough to allow rays to take different paths.
Solution monomode fibres has very narrow core confines light to one signal path.

Question 19

Describe Material Dispersion.

Answer 19

Occurs as refractive index of Optical fibre varies with frequency.
Different wavelengths of light in signal travel different speeds.
Causes sharp pulse to spread into broader therefore duration pulse increases (pulse broadening.)
Problem with this limits maximum frequency of pulses therefore bandwidth available.