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An electric motor runs a D.C. source of ...

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:

A

`2Omega`

B

`8 Omega`

C

`12 Omega`

D

`16 Omega`

Text Solution

Verified by Experts

The correct Answer is:
C
c) Input power, VI=`200 xx 10 = 2000W`
Output power = Efficiency x Input power
`=40/100 xx 2000= 800W`
Power loss in heating the armature
`=2000-800=1200W`
`therefore I^(2)R=1200`
or `R=1200/I^(2) = 1200/(10 xx 10)`
or `R=12Omega`
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