To convert a galvanometer into an ammeter, one should connect :

Concept:

• To convert a galvanometer into an ammeter, a shunt resistor is connected in parallel with the galvanometer.
• A shunt resistor is a low resistance wire or a coil that is connected in parallel with the galvanometer to divert most of the current away from the galvanometer.
• The shunt resistor is designed to have a very low resistance so that most of the current flows through it instead of the galvanometer.
• By connecting the shunt resistor in parallel with the galvanometer, the total current is split between the shunt resistor and the galvanometer.
• The amount of current that flows through the galvanometer is then proportional to the voltage drop across it.
• By selecting an appropriate value for the shunt resistor, the current that flows through the galvanometer can be kept within its range, and the galvanometer can be used as an ammeter to measure higher currents.

The value of the shunt resistor is selected such that the full-scale deflection of the galvanometer occurs when the maximum current to be measured flows through the ammeter. The value of the shunt resistor is calculated using the following formula:

Rs = \(G(\frac{I_g}{I_m} - 1)\)

where:

Rs is the resistance of the shunt resistor
G is the resistance of the galvanometer
I_g is the full-scale deflection current of the galvanometer
I_m is the maximum current to be measured by the ammeter
The shunt resistor should have a very low resistance compared to the resistance of the galvanometer to ensure that most of the current flows through it.

The value of the shunt resistor should also be such that it can handle the maximum current to be measured without getting damaged or changing its resistance value

The correct answer is option (3).