State the principle of superposition.

When two or more waves meet at a point, the resultant displacement at that point is the vector sum of the displacements each wave would produce there on its own.

A wave of amplitude 5.0 cm meets a wave of amplitude 3.0 cm in antiphase. State the amplitude of the resultant.

The resultant amplitude is 5.0 − 3.0 = 2.0 cm, and the resultant is in phase with the larger of the two waves.

Define constructive interference.

Constructive interference occurs where waves meet in phase, so that their displacements add and the resultant amplitude is larger than that of either wave alone.

CCEA A-Level Physics 1210

Physical Quantities, Scalars and Vectors

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Superposition, Interference and Diffraction

Superposition of waves

3 things to know
Unit AS 2

Overview

Principle of superposition, graphical addition of two waves and constructive interference.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is meant by the graphical addition of two waves?

Key term

Two waves of amplitude 3.0 cm meet in phase. State the amplitude of the resultant.

Key term

Two waves of amplitude 3.0 cm meet exactly in antiphase. State the amplitude of the resultant.

Questions from this subtopic

Each one with the model answer underneath.

1
State the principle of superposition.
Model answer
When two or more waves meet at a point, the resultant displacement at that point is the vector sum of the displacements each wave would produce there on its own.
2
What is meant by the graphical addition of two waves?
Model answer
The two wave shapes are drawn on the same axes and, at every position along the axis, the two displacements are added together taking their signs into account, and the resulting values are joined up to give the resultant wave.
3
Two waves of amplitude 3.0 cm meet in phase. State the amplitude of the resultant.
Model answer
The resultant amplitude is 3.0 + 3.0 = 6.0 cm, because the displacements are in the same direction at every instant.
4
Two waves of amplitude 3.0 cm meet exactly in antiphase. State the amplitude of the resultant.
Model answer
The resultant amplitude is zero, because the two displacements are always equal and opposite and cancel completely.
5
A wave of amplitude 5.0 cm meets a wave of amplitude 3.0 cm in antiphase. State the amplitude of the resultant.
Model answer
The resultant amplitude is 5.0 − 3.0 = 2.0 cm, and the resultant is in phase with the larger of the two waves.
6
Define constructive interference.
Model answer
Constructive interference occurs where waves meet in phase, so that their displacements add and the resultant amplitude is larger than that of either wave alone.

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