Question

Two lamps one rated 100 watt and 200 volt and other 200 weight at 220 volt are connected in parallel and in series to the electric main supply of 220 volt and the current drawn in each case

Answer 1

HI !

Power = P = 100 W
Voltage = V = 220v
Resistance = R

P = V²/R
100 = 220 ×220/R
R = 220 × 220/100
= 484 Ω
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Power = P = 60 W
Voltage = V = 220v
Resistance = R

P = V²/R
60 = 220 × 220/R
R = 220× 220/60
= 806.7 Ω
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As the resistors are connected in parallel ,
total resistance = 1/R

1/R = 1/484 + 1/806.7
= 806.7 + 484/484×806.7
= 1290.7/390442.8
R = 390442.8/ 1290.7 = 302.5 ohms

Total resistance = 302.5 Ω


I = current

V = IR
220 = I × 302.5

I = 220/302.5
= 0.73 A

The current drawn is 0.73 A