12: Superposition

Question 1

Principle of Superposition

Answer 1

When two or more waves of the same type meet at a point in space, the resultant displacement of the waves at any point is the vector sum of the displacement due to each wave acting independently.

Question 2

Stationary waves

Answer 2

Stationary waves are waves whose waveform does not advance and there is no translation of energy. The amplitude of the waves varies according to the position from zero at the nodes to a maximum at the antinodes.

Question 3

Conditions for stationary wave:

Answer 3

• 2 progressive waves
• same amplitude
• same frequency
• same speed
• opposite direction
• superpose

Question 4

Diffraction

Answer 4

Diffraction is the spreading of waves at an edge or a slit so that the waves do not travel in straight lines.

Question 5

Coherence

Answer 5

Sources are coherent if they have a constant phase difference.

Question 6

Interference

Answer 6

Interference is the superposing of two or more coherent waves to produce regions of maxima and minima in space, according to the principle of superposition.

Question 7

Conditions for observable interference pattern (4)

Answer 7

1. Waves must OVERLAP / MEET at a point to produce regions of maxima and minima.
2. Sources must be COHERENT.
3. Waves must have (approximately) the SAME AMPLITUDE.
4. Waves must be UNPOLARISED / SAME PLANE OF POLARISATION.