State two ways in which resonance differs from forced vibrations. 

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.

23.

Calculate the equivalent resistance between P and Q from the following diagram: 

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

A cell is sending current in an external circuit. How does the terminal voltage compare with the e.m.f. of the cell? 

What is the purpose of using a fuse in an electrical circuit. 

What are the characteristic properties of fuse wire?

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?

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.