K.C.S.E Physics Q & A - MODEL 2007PP2QN17

K.C.S.E Physics Q & A - MODEL 2007PP2QN17

​(a) State Lenz's Law of electromagnetic induction 
(b) Figure 13 shows a simple microphone in which sound waves from the person talking cause the cardboard diaphragm to vibrate

(i) Explain how a varying current is induced in the coil when the diaphragm vibrates 
(ii) State two ways in which the induced current in (i) above can be increased
(c) A transformer with 1200 turns in the primary circuit and 120 turns in the secondary circuit has its primary circuit connected to a 400V a.c source. It is found that when a heater is connected to the secondary circuit, it produces heat at the rate of 600w. Assuming 100% efficiency, determine the:
(i) Voltage in the secondary circuit 
(ii) Current in the primary circuit 
(iii) The current in the secondary circuit 

answers