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13. A Girl tries to find the frequency of a tuning fork using Sonometer apparatus. a) What is the nature of wave produced in a sonometer. b) Explain why the paper rider thrown away at a particular resonating length. c) Explain how the girl finds the unknown frequency. 1+2+2=5

a) It should be a stationary transvers wave.

b)Basically the frequency f of a stretched string depends upon the length of the string l, the tension T, and the mass per unit length m. Defined by relation f=1/2l v(T/m). The wire is made to vibrate by passing AC current of unknown frequency and when frequency of stretched string is in resonance with AC source frequency then the frequency of AC mains n is equal to the frequency f of wire.why this the paper rider thrown away at a particular resonating length
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c)

Procedure for measuring the AC frequency using a sonometer


1. Set the sonometer as explained.
2. Arrange the electromagnet in a clamp stand and hold it 2-3 mm vertically above the center of the steel wire of the sonometer. Connect the sonometer to secondary of the step-down transformer and connect the D.C. supply to electromagnet, switch on the D.C. and test the magnetization of the electro-magnet with the help of iron needle.
3.Cut a V-shaped light paper rider about one cm long and 2 mm wide. Bring the two knife edges close to each other and place the rider on the wire in between the knife edges. See that the pole of the electromagnet is just above the center of the sonometer wire.
Now gradually increase the distance the two knife edges till the rider begin to flutter. At this stage, make the adjustment very carefully till the rider flies off at a certain fixed distance between the two knife edges. The wire is now in resonance with the frequency of the A.C. mains supply. Measure the length of the wire between the knife edges with a meter rod.
4. Increase the distance between the two knife edges by a few centimeter. Repeat the above process by decreasing slowly the distance between the two knife edges till the rider again flies off. Measure the length of the wire between the two knife edges again. The mean of the two length is the true resonant length.
5. Weigh the weights suspended including the hanger with a trip-scale balance.
6.Increase the weight by half a kilogram and repeat the observation to find the length of the wire vibrating in resonance with A.C. mains supply. Take such four observations by changing the load by 1/2 kg each time.
7. Remove the wire to find the mass per unit length of the wire used. Measure the length of the wire and weight accurately by a sensitive balance.


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