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?

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







Hence, the shunt resistance is 0.125Ω .


1