Current Electricity Ques 77
77. Six similar bulbs are connected as shown in the figure with a DC source of emf E, and zero internal resistance.
The ratio of power consumption by the bulbs when (i) all are glowing and (ii) in the situation when two from section $A$ and one from section $B$ are glowing, will be:
(a) $4: 9$
(b) $9: 4$
(c) $1: 2$
(d) $2: 1$
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Answer:
Correct Answer: 77.(b)
Solution:
- (b) When all bulbs are glowing
$\mathrm{R} _{\mathrm{eq}}=\frac{\mathrm{R}}{3}+\frac{\mathrm{R}}{3}=\frac{2 \mathrm{R}}{3}$
Power $(P_i)=\frac{E^{2}}{R _{\text{eq }}}=\frac{3 E^{2}}{2 R} \quad$ ….(i)
When two from section $A$ and one from section $B$ are glowing, then
$R _{\text{eq }}=\frac{R}{2}+R=\frac{3 R}{2}$
Power $(P_f)=\frac{2 E^{2}}{3 R} \quad$ ….(ii)
Dividing equation (i) by (ii) we get
$\frac{P_i}{P_f}=\frac{3 E^{2} 3 R}{2 R 2 E^{2}}=9: 4$
BETA
