Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Standing Waves on a String

Objective

To make standing wave on a string with an oscillator-vibrator system.

Introduction

This demo uses an oscillator which is an electronic instrument generating sinusoidal voltage waveform of a frequency that can be controlled. The vibrator is an instrument that can vibrate when sinusoidal signal is applied to it. Audio speaker is used as a vibrator. As voltage from the oscillator is applied to the speaker, it vibrates. A small plastic cap with a hole is fixed on the central hub of the speaker. As the speaker vibrates, this cap also vibrates up and down with the same frequency.

Apparatus

an oscillator giving sinusoidal voltage signal of few hertz frequency, an eliminator, a vibrator which can be made from audio speaker.

Procedure

Connect one end of a string to the cap of the vibrator and the other end to the fixed object. The distance between two ends may be few meters. Do not make the string tight. Connect the oscillator to the vibrator and slowly increase the frequency from very low value.

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Discussion

We will see the fundamental mode, first overtone, second overtone etc.\ clearly on the string.