Propagation Of Light

Question 1

Continuous waves and wave pulses

Answer 1

Continuous waves: uninterrupted/continuous wave of light.
Wave pulses: pulses of light, such as flashing light with gaps in between

Question 2

Define the following: Wavelength, Velocity, Frequency and Amplitude

Answer 2

Wavelength: distance between two waves, this could be crest to crest or trough to trough. Measured in nano meters and shown as a ‘lambda’ (line giraffe).

Velocity: speed of each wave within a given time. Measured in ms-1 and shown as ‘v’.

Frequency: number of each wave within a given time (normally a second). Measured in Hz (hertz) and ‘f’.

Amplitude: distance from centre line troop of crest or bottom of trough (bigger the wave the more energy it has). Measured in meters per second and shown as a curly ‘a’.

Question 3

Difference between longitudinal and transverse waves

Answer 3

Longitudinal waves: parallel to the direction of wave travel.

Transverse waves: right angles to the direction of wave travel.

Question 4

Relationship between velocity, wavelength and frequency

Answer 4

Remember the triangle!

Velocity = frequency x wavelength

Frequency = velocity / wavelength

Wavelength = velocity / frequency

Question 5

Understand what is meant by wavefront

Answer 5

Wavefront is the imaginary surface used to represent the vibrating part of the wave.

Question 6

Huygens’ contrusction

Answer 6

States that every point on a wave front acts as a source to secondary waves (wavelets). These waves propagate outwards/forwards forming a common tangent which forms the next wavefront.

Question 7

Define: converging light, diverging light and the parallel pencils of light

Answer 7

Converging light: eventually will come to a focus point along the optical axis.

Diverging light: moves further away from the optical axis and will not form a focus point.

Parallel light: never forms a focus point along the optical axis but will also not move further apart from one another.

Question 8

Define vergence

Answer 8

Vergence is the angle formed by rays of light that are not parallel to one another (either converging or diverging).
Measured in diopters.

Question 9

Define curvature of a wavefront

Answer 9

Curvature of a wavefront is how curved the wave/ripple is.
The curvature of a wavefront decreases the further away from the front source.

Converging lenses (plus) increases the curvature of a wavefront to converge.

Diverging lenses (minus) decreases the curvature of a wavefront to diverge.

Question 10

Distinguish the difference between point source and extended source

Answer 10

Point source: only forms umbra on a surface e.g a pinhole camera.

Extended source: forms both umbra and penumbra on a surface e.g the sun.

Question 11

Properties of an image formed by a pinhole

Answer 11

The image will be:
-inverted
-no distortion
-image size will increase with length of box
-brightness of image will diminish as size increases