Chapter 11

NCERT
Class 10
Science
Solutions
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 a 220 V line if the maximum allowable current is 5 A?

Question:

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 a 220 V line if the maximum allowable current is 5A?

Answer:

Resistance of each bulb

r = V2/P

r = 220 x 220/ 10

r = 4840Ω

Total resistance

R = 220V/5V

R = 44Ω

Let the number of bulbs be n and for resistance R :

R = r/n

44 = 4840/n

n = 4840/44

n = 110

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