2B

Question 1

Describe what is meant by ‘simple harmonic motion’.

Answer 1

An object in simple harmonic motion oscillates due to a linear restoring force.
(F= -ky)

Question 2

State the two solutions to SHM.

Answer 2

y = Asin(t) and y = Acos(t)

Question 3

State what is meant by ‘damping’

Answer 3

A reduction in the amplitude and energy of an object in SHM.

Question 4

Describe how a stationary wave is produced.

Answer 4

An incident wave and a reflected wave of equal amplitude and frequency interfere.

Question 5

Describe what is meant by a ‘node’ on a stationary wave.

Answer 5

A point where there is no displacement.

Question 6

Describe what is meant by an ‘anti-node’ on a stationary wave.

Answer 6

A point where there is maximum displacement.

Question 7

State the condition for two waves to be coherent.

Answer 7

For waves to be coherent they must have equal phase.

Question 8

Describe when a phase change will occur when light travels from one medium to another

Answer 8

When light travels from a low to a high refractive index medium a  phase change occurs
(low to high gives ). When going from high to low then no phase change occurs.

Question 9

State three examples of interference by division of amplitude.

Answer 9

Thin films, wedge fringes and anti-reflective coatings.

Question 10

State one example of interference by division of wavefront.

Answer 10

Youngs’ double slits.

Question 11

Explain how anti-reflective coatings work.

Answer 11

The ray of light reflected from the top surface of the coating interferes with the ray of light
reflected from the bottom surface of the coating. There is a  phase change for each
reflection. The thickness of the coating is chosen to allow destructive interference to
occur.

Question 12

Explain how thin films produce interference patterns.

Answer 12

The ray of light reflected from the top surface of the thin film interferes with the ray of light
reflected from the bottom surface of the film. There is a  phase change for the reflection
off of the top surface only. The thickness of the film determines which colours interfere
constructively and which interfere destructively.

Question 13

Explain how a wedge of air produces interference patterns.

Answer 13

The ray of light reflected from the bottom surface of the top slide interferes with the ray of
light reflected from the top surface of the bottom slide. The thickness of the wedge of air
varies along the length of the wedge and has thicknesses where constructive interference
and destructive interference occur.

Question 14

Explain why anti-reflective coatings have a purple tinge.

Answer 14

Anti-reflective coatings are set up to cause destructive interference in the middle of the
visible spectra (green). The edges of the visible spectra (red and blue) do not destructively
interfere and mix to give purple.

Question 15

Describe why bright fringes can be observed on a far away screen if laser light is shone
through a double slit.

Answer 15

Waves meet in phase and constructively interfere to produce maxima.

Question 16

Describe why dark fringes can be observed on a far away screen if laser light is shone
through a double slit.

Answer 16

Waves meet exactly out of phase and destructively interfere to produce minima.

Question 17

Describe the effect of changing the wavelength of light on the spacing of fringes in a Youngs’
double slit experiment.

Answer 17

Increasing the wavelength increases the space between fringes. Decreasing the wavelength
decreases the space between fringes.

Question 18

State what is meant by the term ‘unpolarised’.

Answer 18

The electric field vector oscillates in more than one plane.

Question 19

State what is meant by the term ‘plane polarised’.

Answer 19

The electric field vector only oscillates in one plane.

Question 20

Describe what is meant by ‘Brewster’s angle’.

Answer 20

When unpolarised light is incident on a glass or water surface if the incident angle is equal to
Brewster’s angle then the reflected component of light from the surface will be plane
polarised.