Waves

Question 1

Progressive waves

Answer 1

There is a transfer of energy as a result of oscillations, hence they transfer information

Question 2

Stationary waves

Answer 2

No net transfer of energy, traps energy in pockets between nodes

Question 3

Mechanical wave

Answer 3

Waves which need a medium through which to travel

Question 4

Longitudinal waves

Answer 4

The particles of the medium oscillate parallel to the direction of energy transfer

Question 5

Transverse waves

Answer 5

The particles of the medium oscillate perpendicularly to the direction of energy transfer

Question 6

Phase difference

Answer 6

The fraction of an oscillation between two particles or points on the a wave

Question 7

What is polarisation?

Answer 7

A wave is plane polarised if the oscillations are in one direction only and perpendicular to the direction of energy transfer

Question 8

What is a polarising filter?

Answer 8

An object that will absorb the energy from the oscillating electric field of an electromagnetic wave. It consists of long chain molecules perpendicular to the polarising axis.

Question 9

Principle of superposition

Answer 9

When two or more waves meet the resultant displacement is equal to the vector sum of the displacements of each wave

Question 10

How are stationary waves formed?

Answer 10

When a progressive wave is reflected between two fixed points, so two waves with the same frequency and amplitude travelling in opposite directions, meet and superpose/interfere creating regions of nodes and antinodes

Question 11

Phase difference in stationary wave

Answer 11

Oscillating particles between nodes are in phased. Oscillating particles in adjacent segments are in antiphase. Oscillating particles in alternate segments are in phase

Question 12

What is the fundamental mode of vibration?

Answer 12

The pattern of a stationary wave, which appears at the lowest possible resonant frequency for a particular system

Question 13

Define coherence

Answer 13

Two waves are coherent if they have a constant phase difference, and same frequency

Question 14

Define interference

Answer 14

when two or more waves meet and superpose at the point there is a change int the overall intensity

Question 15

What is diffraction?

Answer 15

waves spread due to an obstacle or gap, most notable when the gap spacing is about the same size as the wavelength

Question 16

Describe the intensity profile of single slit diffraction

Answer 16

Wide central maximum with lower intensity maxima half as wide on either side

Question 17

Describe the intensity profile of double slit diffraction?

Answer 17

Same overall shape, with more maxima in a “single slit envelope”

Question 18

What is refraction?

Answer 18

Part of the wave energy is transmitted into another medium, exhibiting refraction i.e. change of direction of wave propagation

Question 19

What is Snells Law

Answer 19

The ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of the velocities, or reciprocal of the ratio of the indices of refraction

Question 20

Define dispersion

Answer 20

Different wavelengths of light propogating through the glass slow down by different amounts since the refractive index varies with wavelength

Question 21

Describe material dispersion

Answer 21

Different wavelengths have different speeds due to different refractive indices within the core, a sharp pulse will spread out into a broader signal - reduce by using a monochromatic beam or shorter repeaters to reform the pulse

Question 22

Describe modal dispersion

Answer 22

Different paths have different lengths so effective time along fibre differs. This is causes pulse broadening and limited bandwidth - reduce by using a monomode fibre

Question 23

What is a monomode fibre?

Answer 23

Fibre with a narrow core and the change in n between core and cladding is small, hence light ray is nearly confined to one single path along the cable