How can standing sound waves be demonstrated in air?

A loudspeaker faces a flat reflecting board, and a microphone moved between them detects loud and quiet points. The quiet points are nodes, half a wavelength apart.

What is resonance in a standing wave system?

Resonance occurs when a system is driven at one of its natural frequencies. The amplitude of the standing wave then becomes very large.

What is the difference between a node and an antinode?

A node is a point of zero amplitude where the medium stays still. An antinode is a point of maximum amplitude midway between two nodes.

How far apart are neighbouring nodes in a standing wave?

Neighbouring nodes are half a wavelength apart. A node and the next antinode are a quarter of a wavelength apart.

CCEA A-Level Life and Health Sciences 0008

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Sound and Light

Standing waves, harmonics and resonance tubes

3 things to know
A2 4

Overview

Forming standing waves on strings and in air, nodes and antinodes, harmonics on strings and in closed pipes, worked wavelengths, and measuring the speed of sound with a resonance tube.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Resonance lengths of 0.160 m and 0.495 m are found with a 512 Hz tuning fork. Calculate the speed of sound.

Process

How is a standing wave formed?

Key term

Describe an experiment to demonstrate standing waves on a string.

Questions from this subtopic

Each one with the model answer underneath.

1
How is a standing wave formed?
Model answer
A standing wave forms when two waves of the same frequency and amplitude travel in opposite directions and superpose. A wave reflected from a fixed end usually provides the second wave.
2
Describe an experiment to demonstrate standing waves on a string.
Model answer
A string is stretched over a pulley by a hanging mass and driven by a vibration generator. The frequency is adjusted until a steady pattern of loops appears.
3
How can standing sound waves be demonstrated in air?
Model answer
A loudspeaker faces a flat reflecting board, and a microphone moved between them detects loud and quiet points. The quiet points are nodes, half a wavelength apart.
4
What is resonance in a standing wave system?
Model answer
Resonance occurs when a system is driven at one of its natural frequencies. The amplitude of the standing wave then becomes very large.
5
What is the difference between a node and an antinode?
Model answer
A node is a point of zero amplitude where the medium stays still. An antinode is a point of maximum amplitude midway between two nodes.
6
How far apart are neighbouring nodes in a standing wave?
Model answer
Neighbouring nodes are half a wavelength apart. A node and the next antinode are a quarter of a wavelength apart.

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