A cell of internal resistance r supplies current to a 6.0Ω resistor and its efficiency is 75%. Find the value of r.

A cell of internal resistance r supplies current to a 6.0Ω resistor and its efficiency is 75%. Find the value of r.

Answer Details

Efficiency = power out put/power input * 100/1
= power out put/ power + that due * 100/1
to internal resistance
=> 75/1 = 12R *100/1
12(R+r)
i.e 75/100 = 6/6+r => 75 (6+r) = 100/*6
i.e 450 + 75r = 600
75r =600 - 450
i.e r = 150/75 = 2Ω
i.e r = 2Ω