An electric motor operating on a `60 V` dc supply draws a currrent of `10A`. If the effeciency of the motor is `50%`, the resistance of its winding is

Answer

`2.9 Omega`

Explanation

Here `V = 50 V, l = 12 A eta = 30%`
input power `P = VI = 50 xx 12 W`
power dissipated as heat `p = 100 - 30 = 70% `of input power `= (70)/(100) xx (50 xx 12) = 420 W`
But power dissipated qas heat is
`p' = l^(2) R or 420 = (12)^(2) xx R or R = (420)/(144) = 2.9 Omega`