Wave Phenomena

Question 1

Angular frequency

Answer 1

equal to the angular speed that an object undergoing uniform circular motion would have were it to match the SHM (units = rads^-1)

Question 2

Maximum value of velocity SHM

Answer 2

= ωxo

Question 3

Maximum value of acceleration in SHM

Answer 3

as a = -ω^2x and maximum aceleration occurs at maximum displacement
then = - -ω^2xo

Question 4

Maximum value of force in SHM

Answer 4

as F = ma
= -m -ω^2xo

Question 5

Damping

Answer 5

total energy of SHM will decrease over time due to frictional forces converting Ek to heat energy
light damping = exponential decrease in amplitude
critical damping = motion stops first time the equilibrium position is reached
during damping the amplitude of the oscillation decreases but the frequency and period of oscillation is unchanged

Question 6

Single Slit Diffraction

Answer 6

an interference pattern can be created with a single slit as the two edges of the slit each act as a wave source due to diffraction
interference will occur between the two wave sources to form a pattern of light and dark bands
the wider central maximum is created by rays passing straight through the slit, these waves have all travelled the same distance so meet in phase (constructive interference)
the first minimum is created by waves travelling at an angle as they have been diffracted by the edges of the slit so they do not all travel the same distance and meet out of phase (destructive interference)

Question 7

Effect of slit width (b) on the single slit diffraction pattern

Answer 7

a wider slit will produce:
- higher intensity peaks as more light can pass through
- minima closer together
- a narrower central maximum

Question 8

Effect of wavelength on the single slit diffraction pattern

Answer 8

a greater wavelength will produce:
- minima further apart
- a wider central maximum

Question 9

White light and single slit diffraction

Answer 9

• the central maximum will be white with an orange edge (due to greater diffraction of longer wavelengths of red, orange and yellow)
• the other maxima are rainbows with blue towards centre and red towards outside

Question 10

Modulation

Answer 10

the reshaping of the double slit interference pattern by single slit diffraction

Question 11

Multiple slit diffraction differences to double slit diffraction

Answer 11

the bright fringes are:
- in the same positions as for double slit (for the same slit width and spacing)
- narrower (more overlapping patterns)
- brighter (intensity is proportional to the square of the number of slits)

this is because more slits give more wave sources for interference and also allow more light through to create the pattern

Question 12

Diffraction grating interference patterns

Answer 12

the interference pattern is:
- sharper because more slits create more wave sources that can interfere
- brighter because more light can pass through the greater number of slits

if the distance between slits does not change then maxima occur in the same positions

Question 13

Thin film interference

Answer 13

a thin film is a thin layer of material that has a different refractive index than its surroundings
thin films cause incident light to undergo interference which may be destructive or constructive depending on the wavelength of the light and the thickness of the film
as light is reflected off a medium of higher refractive index it will undergo a 180 degrees phase change but will not undergo phase change if it reflects off a surface of lower refractive index

Question 14

Resolution

Answer 14

ability to detect the two light sources as separate

Question 15

Rayleigh Criterion

Answer 15

the maximum of one diffraction pattern is over the first minimum of the other

Question 16

how do you find source angle to compare to raighleigh’s criterion angle

Answer 16

if distance between sources is much much smaller than distance to the sources then:
source angle = distance to sources/distance between sources

Question 17

Resolvance def.

Answer 17

the ratio between the wavelength being investigated and the smallest possible resolvable wavelength difference

Question 18

Doppler Effect def.

Answer 18

the change in the observed frequency of a wave when there is relative motion between the wave source and the observer

Question 19

Key things to remember for Doppler Effect with moving source for mechanical waves

Answer 19

the speed of the wave does not change
if source is approaching use v-us
if source is moving away use v+us
Doppler effect only becomes noticeable if the speed of the source is significant relative to the speed of the wave

Question 20

Key things to remember for Doppler Effect with moving observer for mechanical waves

Answer 20

wavelength is the same
if the observer is approaching use v+uo
if the observer is moving away use v-uo

Question 21

Doppler effect for light waves

Answer 21

formula can only be used if the velocity of the source or the observer is much smaller than the speed of light