K.C.S.E Physics Q & A - MODEL 2008PP2QN18

K.C.S.E Physics Q & A - MODEL 2008PP2QN18

​(a) Figure 12 shows two circuits close to each other

​When the switch is closed, the galvanometer shows a reading and then returns to zero. When the switch is then opened, the galvanometer shows a reading in the opposite direction and then returns to zero. Explain these observations. 
(b) Explain how energy losses in a transformer are reduced by having:
(i) A soft- iron core 
(ii) A laminated core 
(c) An ideal transformer has 2000 turns in the primary circuit and 200 turns in the secondary circuit. When the primary circuit is connected to a 400V a.c. source, the power delivered to a resistor in the secondary circuit is found to be 800W. Determine the current in:
(i) The secondary circuit
(ii) The primary circuit

answers