Two points on a wave of wavelength 1.2 m are 0.30 m apart. What is their phase difference?

The phase difference is 90°, or π/2 radians. The working is (0.30 ÷ 1.2) × 360° = 90°.

Two waves of period 8.0 ms are offset in time by 3.0 ms. What is their phase difference?

The phase difference is 135°, or 3π/4 radians. The working is (3.0 ÷ 8.0) × 360° = 135°.

Two points on a wave are 1.5 wavelengths apart. What is their phase difference?

Points 1.5 wavelengths apart are in antiphase, a phase difference of 180°. The extra whole wavelength adds a full cycle, which does not change the phase relationship.

CCEA A-Level Life and Health Sciences 0008

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Sound and Light

Phase difference and the electromagnetic spectrum

3 things to know
A2 4

Overview

Phase difference, in phase and antiphase with worked examples, the electromagnetic spectrum and its shared features, visible wavelengths, a frequency calculation, and why ultraviolet is harmful.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is phase difference?

Key term

What does it mean for two points on a wave to be in phase?

Key term

What does antiphase mean?

Questions from this subtopic

Each one with the model answer underneath.

1
What is phase difference?
Model answer
Phase difference describes how far one oscillation is ahead of or behind another. Phase difference is measured as a fraction of a cycle, in degrees or radians.
2
What does it mean for two points on a wave to be in phase?
Model answer
Two points in phase move in exactly the same way at the same time. Points in phase are separated by a whole number of wavelengths.
3
What does antiphase mean?
Model answer
Two waves in antiphase are half a cycle, 180° or π radians, out of step. A crest of one arrives at the same time as a trough of the other.
4
Two points on a wave of wavelength 1.2 m are 0.30 m apart. What is their phase difference?
Model answer
The phase difference is 90°, or π/2 radians. The working is (0.30 ÷ 1.2) × 360° = 90°.
5
Two waves of period 8.0 ms are offset in time by 3.0 ms. What is their phase difference?
Model answer
The phase difference is 135°, or 3π/4 radians. The working is (3.0 ÷ 8.0) × 360° = 135°.
6
Two points on a wave are 1.5 wavelengths apart. What is their phase difference?
Model answer
Points 1.5 wavelengths apart are in antiphase, a phase difference of 180°. The extra whole wavelength adds a full cycle, which does not change the phase relationship.

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