Question

Current is measured with an instrument which is called a (an) ...................
(A) Ammeter
(B) Voltmeter
(C) Meter Bridge
(D) Galvanometer.

Answer 1

Hint: We need to define each device one by one. We can remember the SI unit of current is Ampere. We need to use this to determine, which one measures current. It should be a device such that it should not cause significant voltage drop for accurate measurements.

Complete answer:
We define ammeter, voltmeter, meter-bridge and galvanometer one by one.
An ammeter (from ampere meter) is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes (A), hence the name. The ammeter is usually connected in series with the circuit in which the current is to be measured. An ammeter usually has low resistance so that it does not cause a significant voltage drop in the circuit being measured.
Voltmeter is a voltage meter. Which measures the voltage between the two nodes. We know the unit of potential difference is volts. So it is a measuring instrument which measures the potential difference between the two points.
The main principle of voltmeter is that it must be connected in parallel in which we want to measure the voltage. Parallel connection is used because a voltmeter is constructed in such a way that it has a very high value of resistance. So if that high resistance is connected in series then the current flow will be almost zero which means the circuit has become open.
A meter bridge also called a slide wire bridge is an instrument that works on the principle of a Wheatstone bridge. A meter bridge is used in finding the unknown resistance of a conductor as that of in a Wheatstone bridge. A Wheatstone bridge is a kind of electrical circuit used in measuring an electrical resistance, which is unknown by balancing its two legs of the bridge circuit, where one of the legs includes an unknown component.
A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. A galvanometer works as an actuator, by producing a rotary deflection of a pointer, in response to electric current flowing through a coil in a constant magnetic field.
The device used to measure current is ammeter.
Hence, the correct answer is Option A.

Note:
There are two ways to measure electricity; one is by measuring current where ammeter is being used and another by measuring the voltage where voltmeter is being used. Both of these devices are used in electric circuits but the major difference between voltmeter and ammeter is ammeter comes in handy for measuring the flow of current whereas the voltmeter comes in handy for measuring the voltage or emf across two points in an electric circuit.
The major significant difference between ammeter and galvanometer is that ammeter shows only the magnitude of the current. Whereas, the galvanometer shows both the direction and magnitude of the current.