Question

A dynamo dissipates 20 w when it supplies a current of 4a through it if the terminal potential difference is 220v them the emf produced is

Answer 1

Given that

Power, P = 20 W

Current, I = 4 A

Terminal Potential , Vt = 220 V

We know that,

Power, P=I^2/R

Resistance, R=P/I^2=20/4^2=5/4 Ω

EMF produced by dynamo is given by:

ε=Vt+IR=220+4×5/4=220+5=225 V

Answer 2

Concept Introduction: Dynamo produces current in the form of AC.

Given:

We have been Given:

$p = 20w \\ i = 4a \\ v_{t} = 220v$

To Find:

We have to Find: The EMF produced.

Solution:

According to the problem,

Resistance is given by

$r = \frac{ {i}^{2} }{p}$

putting the values, we get,

$r = \frac{ {4}^{2} }{20} = \frac{16}{20} = \frac{4}{5} ohm$

Now, EMF is given by

$e = v_{t} + ir$

therefore, putting the values, we get,

$e = 220 + 4 \times \frac{4}{5} \\ e = 220 + \frac{16}{5} \\ e = \frac{1100 + 16}{5} \\ e = \frac{1116}{5} \\ e = 223.2v$

Final Answer: The EMF produced is,

$e = 223.2v$

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