Page 50 - CHAPTER-1 (Electricity)

CHAPTER 1

ELECTRICITY

Ans.The resistance of each bulb, r = V 2 = (220) 2 =4840Ω
P 10

The total resistance in the circuit, R = 220V =44Ω
5A
Let n be the number of bulb (each of resistance r) to be

connected in parallel to obtain a resistance R.

r

Clearly, R = or n = = 4840Ω =110
R 44Ω
6. A hot plate of an electric toaster connected to a 220 V line has two

resistance coils, each of 24Ω resistance, named A and B. These

coils may be used separately, in parallel, or in series. Compute the

currents in the three cases?

Ans. Here, potential drop, V = 220 V

The resistance of both the coils, r = 24

(i) If we connect each of the coils A or B, separately, the current

through each coil, i.e.,

V
I = = 220V =9.2A
r 24Ω

(ii) When the coils A and B are joined in parallel combination,

r
equivalent resistance in the circuit,R = = 24Ω =12Ω
p
2
2
V
Current through the parallel combination, i.e., I = R p = 220V =18.3A
p
12Ω
(iii) When the coils A and B are joined in series combination,

equivalent resistance in the circuit,

R = r + r = 2r = 48
s
V
Current through the series combination, i.e., I = = 220V =4.6A
s
R
48Ω
s

48