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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?
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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