Current Electricity and Electrical InstrumentHard

Question

A moving coil galvanometer of resistance $100\Omega$ shows a full scale deflection for a current of 1 mA . The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA , is $\_\_\_\_$ $\Omega$

Options

A.25
B.10
C.0.5
D.2.5

Solution

$$\begin{matrix} & G = 100\Omega \\ & i_{g} = 1\text{ }mA \\ & i = 5\text{ }mA \\ & r_{s} = \frac{G}{\left( \frac{i}{i_{g}} - 1 \right)} \\ & \ = \frac{100}{\left( \frac{5}{1} - 1 \right)} = 25\Omega \end{matrix}$$

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