Short Answer TypeState two ways in which resonance differs from forced vibrations.
| Resonance | Forced Vibrations |
| 1. Vibrations are of large amplitude | 1. Vibrations are usually of small amplitude. |
| 2. Frequency of an external applied periodic force is equal or an integral multiple to the natural frequency of the body. | 2. Frequency need not be equal or integral multiple to the natural frequency of the body. |
i) A man standing between two cliffs produces a sound and hears two successive echoes at intervals of 3 s and 4 s respectively. Calculate the distance between the two cliffs.
The speed of sound in the air is 330 m/s.
ii) Why will an echo not be heard when the distance between the source of a sound and the reflecting surface is 10 m.
d) An electrical appliance is rated at 1000 KVA, 220 V. If the appliance is operated for 2 hours, calculate the energy consumed by the appliance in:
i) kWh
ii) jouleA cell is sending current in an external circuit. How does the terminal voltage compare with the e.m.f. of the cell?
i) Write an expression for the electrical energy spent in the flow of current through an electrical appliance in terms of I,R and t.
ii) At what voltage is the alternating current supplied to our houses?
iii) How should the electric lamps in a building be connected?
i) What is an a.c. generator or dynamo used for?
ii) Name the principle on which it works?The diagram below shows a current carrying loop or a circular coil passing through a sheet of cardboard at the points M and N. The sheet of cardboard is sprinkled uniformly with iron fillings. 
i) Copy the diagram and draw an arrow on the circular coil to show the direction of current flowing through it.
ii) Draw the pattern of arrangement of the iron fillings when current is passed through the loop.
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