Physics 9702 · Paper 1

Superposition

Definitions: Superposition

One exam question, the mark-scheme answer, and the exact phrases that score (highlighted, then listed below in the same colour).

Exam question

State the principle of superposition.

1 mark

Model answer

When two (or more) waves meet at a point, the resultant displacement is the sum of the individual displacements.

Marking points

1 mark each

1resultant displacement is the sum of the individual displacements(1)

Exam question

State what is meant by two coherent sources.

1 mark

Model answer

Two sources are coherent when they have a constant phase difference.

Marking points

1 mark each

1constant phase difference(1)

Exam question

State the conditions for constructive and for destructive interference.

2 marks

Model answer

Constructive: the waves arrive in phase (path difference = $n\lambda$ ), so displacements add to a maximum. Destructive: the waves arrive in antiphase (path difference = $(n + \tfrac{1}{2})\lambda$ ), so they cancel.

Marking points

1 mark each

1in phase (path difference = $n\lambda$ ), so displacements add to a maximum(1)
2in antiphase (path difference = $(n + \tfrac{1}{2})\lambda$ ), so they cancel(1)

Exam question

State what is meant by diffraction.

1 mark

Model answer

Diffraction is the spreading of a wave as it passes through a gap (or past an edge).

Marking points

1 mark each

1spreading of a wave as it passes through a gap (or past an edge)(1)

Exam question

State how a stationary wave forms, and define a node and an antinode.

3 marks

Model answer

A stationary wave forms when two waves of the same frequency (and speed) travel in opposite directions and superpose. A node is a point of zero amplitude; an antinode is a point of maximum amplitude.

Marking points

1 mark each

1two waves of the same frequency (and speed) travel in opposite directions and superpose(1)
2zero amplitude(1)
3maximum amplitude(1)

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Superposition

Definitions: Superposition

One exam question, the mark-scheme answer, and the exact phrases that score (highlighted, then listed below in the same colour).

Exam question

State the principle of superposition.

1 mark

Model answer

When two (or more) waves meet at a point, the resultant displacement is the sum of the individual displacements.

Marking points

1 mark each

1resultant displacement is the sum of the individual displacements(1)

Exam question

State what is meant by two coherent sources.

1 mark

Model answer

Two sources are coherent when they have a constant phase difference.

Marking points

1 mark each

1constant phase difference(1)

Exam question

State the conditions for constructive and for destructive interference.

2 marks

Model answer

Marking points

1 mark each

1in phase (path difference = $n\lambda$ ), so displacements add to a maximum(1)
2in antiphase (path difference = $(n + \tfrac{1}{2})\lambda$ ), so they cancel(1)

Exam question

State what is meant by diffraction.

1 mark

Model answer

Diffraction is the spreading of a wave as it passes through a gap (or past an edge).

Marking points

1 mark each

1spreading of a wave as it passes through a gap (or past an edge)(1)

Exam question

State how a stationary wave forms, and define a node and an antinode.

3 marks

Model answer

A stationary wave forms when two waves of the same frequency (and speed) travel in opposite directions and superpose. A node is a point of zero amplitude; an antinode is a point of maximum amplitude.

Marking points

1 mark each

1two waves of the same frequency (and speed) travel in opposite directions and superpose(1)
2zero amplitude(1)
3maximum amplitude(1)