An electric motor runs a `D.C.` source of e.m.f. `200 V` and draws a current of `10A`. If the efficiency is `40%`, then ressistance of the armature is:

Options

A. `2Omega`
B. `8Omega`
C. `12Omega`
D. `16Omega`

Answer

C

Explanation

Input power=VI=`200xx10=2000W`
Output power`=(40)/(100)xx2000=800W`
Power loss in heating the armature
`=2000-800=1200W`
`I^(2)R=1200`
or `R=(1200)/(I^(2))=(1200)/(10xx10)` or `R=12Omega`