First slide

Electrical measuring instruments

Question

A galvanometer having coil resistance $100 Ω$ gives a full scale deflection when a current of $10 mA$ is passed through it. What is the value of the resistance which can convert this galvanometer into a voltmeter giving full scale deflection for a potential difference of 10 V ?

Easy

A

$900 Ω$
B

$9.9 K Ω$
C

$8.9 K Ω$
D

$999 K Ω$

Solution

$V_{g} = i_{g} R_{g} = 10 \times 10^{- 3} \times 100 = 1 V V=10V \begin{array}{l} {R=R}_{g} [\frac{V}{V_{g}} - 1] = 100 \times [\frac{10}{1} - 1] = 100 \times 9 = 900 Ω \\ A l t e r n a t e m e t h o d : \\ R = \frac{V}{i_{g}} - G = \frac{10}{10 \times 10^{- 3}} - 100 = 1000 - 100 = 900 Ω \end{array}$

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