Question

Briefly describe the conversion of a galvanometer into an ammeter.

Answer 1

To answer this question, we have to look for the basic working principle of the galvanometer. An ammeter is always connected in series with the circuit, so we have to look for the condition that it doesn’t affect the original value of the current in the circuit.

Complete step by step solution:
A galvanometer is a device which works on the principle that when a current carrying loop is placed in a magnetic field, it experiences a torque. It consists of a coil placed in a uniform radial magnetic field, which is set free to rotate about a fixed axis. When a current flows through this coil, it experiences a torque which produces a deflection in its pointer which is read as current.
So, a galvanometer shows a deflection whenever current flows through it. Therefore it can be used to measure the current. But it cannot be used directly as an ammeter because it is a very much sensitive device which shows full deflection even for very small amounts of currents (of the order of $\mu A$). Also, it has a very high resistance. So, connecting it in series in the circuit increases the net resistance of the circuit and hence affects the value of the original current.
Both these limitations are overcome by connecting a shunt wire of very low resistance in parallel to the galvanometer. So, most of the current passes through this shunt resistance. Let the resistance of the galvanometer be $G$ and that of the shunt wire be $S$. So, the equivalent resistance of the galvanometer is
$\Rightarrow R = \dfrac{{GS}}{{G + S}}$
For $S < < G$
$\Rightarrow R \approx S$
Thus the resistance of the galvanometer is reduced to a much lower value.
Hence, a galvanometer is converted to an ammeter by connecting a shunt wire of very much low resistance in parallel.

Note:
Besides being used as an ammeter, a galvanometer has many more applications in the different fields. It is used as a voltmeter, which is used to measure the potential difference between two points inside a circuit. In fact it is modified in different ways to act as a basis for any type of a moving coil measuring device. One more example of such a device is the ohmmeter which is used for measuring the resistance.