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?
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