Question

Two lamps, one rated 100W ; 220V, and the other 60W ; 220V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line , if the supply voltage is 220V .

Answer 1

P1=100 W , V = 220 V , P2= 60 W (GIVEN)

I1 = ? I2 = ?

P1= VI1

. : I1=P1/ V

= 100/220 = 0.46A

SIMILIARLY ,

I2=P2/ V = 60/220

= 0.27A

TOTAL CURRENT (I) = I1 + I2

= 0.46 + 0.27

Answer 2

Answer:

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

Explanation: