a dynamo dissipates 20 watt when it supplies a current of 4 A through it. if the terminal potential difference is 220V then the emf produced is ?

ans: 225V

how? plz explain.

Given that
Power, P = 20 W
Current, I = 4 A
Terminal Potential , Vt = 220 V

We know that
Power, P=I2RResistance, R=PI2=2042=54 Ω
EMF produced by dynamo is given by
ε=Vt+IR=220+4×54=220+5=225 V

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