Question

Two electric bulb rated 100W/220V and 25W/220V are connected to the mains in parallel. What would be the amount of current drawn and also find the resistance of an iron that to be connect to get same current from source of 220V.​

Answer 1

Explanation:

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

Answer 2

...........................0.73A