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A motor having an armature of resistance...

A motor having an armature of resistance 2.0 ohm operates on 220 V mains. At its full speed, it develops a back e.m.f. of 210 V. Find the currents in the armature when motor is switched on and when running at full speed. What is the efficiency ot the motor at full speed ?

Text Solution

Verified by Experts

Here, `R = 2.0 ohm, V = 220 V, E = 210 V`,
When motor is switched on, back e.m.f. `(E = 0)`.
Therefore, `I = (V)/(R ) = (220)/(2.0) = 110 A`
At full speed, `I' = (V - E)/(R ) = (220 - 210)/(2.0) = 5 A`
`eta = (E)/(V) xx 100 = 95.5%`
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