Question

What is an ammeter?
A. A measuring instrument
B. A principle of Physics
C. A type of charge
D. None of the above

Answer 1

An ammeter is an instrument which is used in a circuit to determine the current. To measure electric current through a resistance in the circuit, the ammeter must be connected in series with that resistance.

Complete step by step answer:
Electric current is defined as the rate of flow of electric charge in a circuit. Electric current is denoted by the letter ‘I’.
To determine the direction of current in a circuit, an electric instrument, galvanometer, is used.
Galvanometer can be used in a number of ways. One such use is measuring current. But galvanometer cannot be used as such to measure current because it is a very sensitive device and gives full scale deflection for very small currents of order $\mu A$. We encounter one other problem also to measure current as we need to connect the instrument in series, for current remains same in series. But, galvanometer has very large resistance which will change the value of current in the circuit.

To overcome these problems, we connect a small shunt resistance in parallel with the galvanometer coil; such that most of the current passes through the shunt and this also decreases the combined resistance of the instrument. This arrangement to measure current is known as ammeter.

So, the correct answer is “Option A”.

Note: A galvanometer is a device used to determine the direction of electric current. It is based on the principle that, ‘A current-carrying coil when placed in an external magnetic field experiences magnetic torque. The angle through which the coil is deflected due to the effect of the magnetic torque is proportional to the magnitude of current in the coil.”