The expected answers were:
(a) (i) Energy is the ability to do work.
(ii) Joule or kilowatt-hour, watt-sec.
(b) Is= 8 mA
IR2= 6 mA
:.IR1= Is-IR2 =(8-6) mA = 2 mA
(i) R1=V/IR1
R1= 24/2 mA = 12 kn
(ii) Total resistance, RT =R1RJRl + R2
=4 X 103 x 12 X 103/(4 x103 + 12 X 103)
=48 x 103/16
=3kn
(iii)
Power = Is
2RT
= (8 X 10-3)2 X 3 X 103= 192 mW
OR
= (ld2R2 + (IR1)2R1
= (6 X 10-3)2 x 4 X 103 + {(2 X 10-3)2 X 12 X 103}
= 0.192 watts = 192 mW
The question was on Direct Current Circuit Theory. It was quite popular with
the candidates.
Many of the candidates who attempted the question got it right. However,
only a few could not parallel the resistors correctly.