Question

The armature of a dc motor has 20W resistance. It draws a
current of 1.5 A when run by a 220 V dc supply. The value
of the back emf induced in it is
(a) 150 V (b) 170 V (c) 180 V (d) 190 V

Answer 1

For dc motor, I = [{E – e}/R]

(1) given R = 20 Ω

I = 1.5 A E = 220

V from (1);

E – e = IR

∴ E – IR = e

∴ e = 220 – (1.5 × 20)

e = 190 V

(d) 190 V

Answer 2

The answer is (d) 190 V

EXPLANATION ::

We know that

I = ( E – e) /R

Given R = 20

I = 1.5

E = 220 V

So

E – e = IR

∴ E – IR = e

∴ e = 220 – (1.5 × 20) = 190

Please check it

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