A galvanometer with an internal resistance of 19.8 Ohm can measure current up to 10mA

A galvanometer with an internal resistance of 19.8 Ohm can measure current up to 10mA. Determine the resistance of the shunt included in the circuit so that the force can be measured up to 1 A.

The shunt is connected in parallel with the ammeter. Then, according to Ohm’s law for a section of the circuit, the voltage on the shunt is equal to the voltage on the ammeter:

Ush = Ua = Ish * Rsh = Ia * Ra,

where Ish = 1 – 0.1 = 0.9 A, the current flowing through the shunt at a measured current of 1A;

Ia = 10 mA = 0.1 A – maximum allowable current through the galvanometer;

Ra = 19.8 ohms.

Rsh = Ia * Ra / Ish = 0.1 * 19.8 / 0.9 = 1.98 / 0.9 = 2.2 Ohm.