K.C.S.E Physics Q & A - MODEL 2018PP2QN15

K.C.S.E Physics Q & A - MODEL 2018PP2QN15

​(a) Electrical energy is transmitted at very high voltages and low current
(i) Describe how the high voltages are attained 
(ii) State two reasons why thick aluminum wires are preferred to Copper Wires for transmission Over long distances 
(b) Figure 4 shows an electric cooker connected to the mains supply, X,Y and Z are the mains wires

​State with a reason the name of wire Y. 
(c) A student has some coloured bulbs rated 60 W, 240 V to be connected for decorations.
(i) State the number of such bulbs that can be connected normally to a 240V supply through a 5A fuse. 
(ii) If the cost of electric energy is Ksh 3.00 per kWh, determine the cost of running the bulbs in (c) (i) for 5 hours daily for 20 days. 

answers

(a)(i) By use of step-up transformers low input voltages are stepped up to high voltages for transmission. 
(ii) They are cheaper 
They are lighter, lower density / lower weight
b) Y is the earth wire, it is connected to the casing of the cooker