Question

two lamps one is rated 100w at 200V and the other 60W at 220V are connected in parallel at a 220V supply. find the current drawn from the supply line

Answer 1

Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be same that is 220 V, Current drawn by the bulb of rating 100 W is given by

I=P/V

 =100/220=0.4545...A

Similarly, current drawn by the bulb of rating 60 W is given by

I=P/V

 =60/220=0.2727...A

∴ the total current drawn from the line =0.4545+0.2727=0.727A

Answer 2

Case I
Given:
Power = P = 100 W
Voltage = V = 220v
Resistance = R
   
    P = V²/R
 100 = 220 ×220/R 
   R  = 220 × 220/100     
        = 484 Ω

Case II

Given:
  Power = P = 60 W
Voltage = V = 220v
 Resistance = R

  P = V²/R
60 = 220 × 220/R 
 R = 220× 220/60   
     = 806.7 Ω

As the resistors are connected in parallel , 
total resistance = 1/R₁+1/R₂
                         = 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
 
Then,
     I = current
    V = IR
220 = I × 302.5 
     I = 220/302.5   
       = 0.73 A

The current drawn is 0.73 A

:) Hope this Helps !!!