An ammeter is to be constructed which can read currents up to 2.0 A. If the coil has a resistance of 25Ω and takes 1 mA for full-scale deflection, what should be the resistance of the shunt used?

Question

Philoid · Accepted Answer

Concepts/Formula used:

Ohm’s Law:

Potential Difference (V) across a resistor of resistance R when current I passes through it is given by Ohm’s law:

The maximum current that can be measured is .

The current through the coil when there is full scale deflection is .

The resistance of the coil is

Let the resistance of the shunt be and current when there is full-scale deflection is .

By Kirchhoff’s junction rule,

Using Ohm’s law, we have

and

As r_s and r are in parallel, the potential difference across them is the same.

Hence, the shunt resistance is 0.125Ω .