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Physics Chemistry

Entry Test MCQ :: Current Electricity


  Three equal resistors connected in series with a source of e m f together dissipate 10 W of power each. What will be the power dissipated if the same resistors are connected in parallel across the same source of e m f?
[A]. 40 W[B]. 90W
[C]. 100W[D]. 120W

Answer: Option B


abdul majid said:    
 
why?please explain it

saeed niazi said:    
 
P=(V.V)/R In series: resistance=3R P=10W so: 10=(V.V)/(3R) =>V=R.sqrt(30)........(1) in parallel: total R= (R.R.R)/(R+R+R)=RRR/3R=RR/3 P=(V.V)/R P={R.sqrt(30).R.sqrt(30)}/(RR/3) :from (1) P={30}/(1/3) P=90W

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