technical question, plz answer with explanation

Ques. An electric bulb is rated 220V and 100W.Wen it is operated on 110V,the power consumed will be? i)100W ii)75W iii)50W iv)25W

  • Arjun
  • 14 Mar
  • 1540 Views
  • 3 Answers
Your Answer

Answer is option 4

Explaination:

Power 

P=I*V 

where I is the current, V is the voltage 

But ohms law says: 

I=V/R 

where R is the resistance 

so: 

P=V^2/R 

so we know that when operated at 220 volts, the power is 100w, so we can work out the resistance: 

R=220^2/100 

R= 484 ohms. 

Now when operated at 110 volts: 

P=V^2/R 
=110^2/484 
=25 Watts 

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