Question

Galvanometer of resistance 100 ohm is converted to ammeter by connecting 10 ohm shunts resistance. Calculate the resistance of ammeter.

Answer 1

For the given galvanometer and shunt resistance, the resistance of the ammeter will be 9.09 Ω.

Given,

A galvanometer is converted into an ammeter.

Galvanometer resistance = 100 Ω,

Shunt resistance = 10 Ω.

To find,

The ammeter resistance.

Solution,

Firstly, a galvanometer can be converted into an ammeter or voltmeter, when required.

A galvanometer is converted into an ammeter by connecting a very low resistance, which is called "Shunt", in parallel with the galvanometer.

Let the galvanometer resistance be $R_g$, and shunt resistance be s.

Then, the ammeter resistance (say R) after it is converted, can be given as

$\frac{1}{R} =\frac{1}{R_g} +\frac{1}{s}$

Simplifying further,

$R = \frac{R_g \times s}{R_g+s} \hfill ...(1)$

Here, it is given that,

$R_g = 100 \Omega$

$s=10 \Omega$

Thus, using (1), the ammeter resistance will be

$R=\frac{100 \times 10}{100 + 10} =\frac{1000}{110} =\frac{100}{11}$

⇒ R = 9.09 Ω.

Therefore, for the given galvanometer and shunt resistance, the resistance of the ammeter will be 9.09 Ω.

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