Question

Question 12
Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A ?​

Answer 1

Resistance R1 of the bulb is given by the expression,

Supply voltage, V = 220 V

Maximum allowable current, I = 5 A

Rating of an electric bulb P=10watts

Because R=V2/P

$r1 = {220}^{2} \div 10 = 4840$

According to Ohm’s law,

V = I R

Let R is the total resistance of the circuit for x number of electric bulbs

R=V/I

=220/5=44 Ω

Resistance of each electric bulb, R1=4840Ω

1/R = 1/R1 + 1/R2 + ... upto x times.

1/R = 1/R1 * x

x = R1/R = 4840/44 = 10

∴ Number of electric bulbs connected in parallel are 110.

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