pHYSICS

Experiment 1

Principle

When AC is passed through the sonometer wire kept under magnetic field perpendicular to the length of the wire, then from Fleming’s left hand rule, a mechanical force acts on the wire and pulls it up and down as the sinusoidal current varies from a

positive to a negative value. Thus, vibrations equal to the frequency of AC supply are forced on the wire. If the natural frequency of the stretched wire, under tension between the bridges A and B, becomes equal to the AC supply frequency then wire vibrates with maximum amplitude. Under the resonance condition, if the length of the wire (l) between

the bridges vibrates as one loop, then we have Frequency (n) of AC supply = Natural frequency of the vibrating loop

Where T= Mg and M = Mass suspended to the wire + Mass of the hanger.

m = mass per unit length of the wire

l = length of the wire between the bridges A and B

Materials required

Sonometer, Metal Wire(s), Weight hanger with loose weights, Coil, A.C power supply

Procedure

The magnetic field acting between the bridges A and B, the tension T in the wire and the length between the bridges is adjusted till the wire vibrates with maximum amplitude. The length ‘l’ of the vibrating loop is noted (if the wire vibrates with more

than one loop, say x loops; then the length ‘l’ of a single loop is equal to the length of the wire between the bridges divided by x). The experiment is repeated by changing T and correspondingly l.

Observations

Mass per unit length of the wire m =

mass of the wire/ length of the wire = …………… kg/m

Result

The frequency of AC supply using Sonometer is……………. Hz

Reference Material

1. Practical Physics. G. L. Squires. 4/e, 2001, Cambridge University Press.

2. Thermal Physics, S. Garg, R. Bansal and C. Ghosh, 1993, Tata McGraw-Hill.

Questions

1. What is resonance?

2. What is a standing wave?

3. What makes the metal wire vibrate?