Question

Two lamps one rated 199 w at 220 v and other 60 w at 220 v ,are connected in parallel to electric mains supply . what current is drawn from the mains if the supply voltage is 220 v

Answer 1

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

Hello friend___❤

Here is your answer ✒

For the 1st lamp:

Power P1 = 100 W and

Potential difference V = 220 V

Therefore,

I1= P1/ V = 100/220 = 0.455 A

For the 2nd lamp:

Power P2 = 60 W and

Potential difference V = 220 V

Therefore,

I2= P2/ V =60/ 220 = 0.273 A

So, the net current drawn from the supply is given by

= I1 + I2 = 0.455 + 0.273 = 0.728

I hope, this will help you___❤❤

Thank you

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