School of Physics Lecture Demonstration Manual

Wb-6 The Monochord (The Sonometer)

Published: Tuesday 14 March 2006 - Updated: Wednesday 30 March 2011

Aim

To demonstrate the fundamental law of vibration of a stretched string.

Apparatus

Diagrams

Click on pictures to enlarge.

Monochord Diagram

Monochord Equation

Description

The monochord consists of a sounding box which supports a wire whose length of vibration may be adjusted by the movable bridge B. The tension is adjustable by the weights D. The equation for the vibration of a stretched string may be verified .

The equation above shows that:

for a string under constant tension the frequency varies inversely as the length;for a string of constant length the frequency is proportional to the square root of the tension;for a given length and constant tension the frequency varies inversely as the square root of the mass/unit length.

which are Mersenne's laws.

Safety notes

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