Question

An ammeter has a range of $(0 - 2)$ Ampere and there are $20$ divisions on its scale. What is its least count?
(A) $10\,A$
(B) $27\,A$
(C) $0.1\,A$
(D) $0.01\,A$

Answer 1

Hint:Here we have to use the formula for least count of ammeter to find the least count of the given question.The least count of any instrument is the minimum value of the parameter that can be determined with the help of the instrument scale and that can be overcome.

Complete step by step answer:
Ampere ammeter is a device for calculating either direct or alternating electric current. An ammeter can quantify a wide variety of current values since only a limited portion of the current is guided into the metre system at high values; the main portion is borne by a shunt parallel to the metre.
There is a pointer on a dial for certain types of ammeter, but most have a digital monitor. We have to link the ammeter in series with it to calculate the current flowing through a part in a circuit.
Given,
Range of ammeter $I = 0 - 2\,A$
Number of divisions on scale $n = 20$
We know that,
Least count of ammeter $ = $ range of ammeter/number of divisions on scale
$
L.C = \dfrac{I}{n} \\
= \dfrac{2}{{20}} \\
= 0.1\,A \\
$
 Hence, the least count is $0.1\,A$ per division.
Therefore, option C is correct.

Note: There should be many things kept in mind while taking the least count of an ammeter. There should be zero error to get the correct measurement. If the ammeter pointer is precisely at zero when it is not attached to the circuit, there is a zero error in the instrument. The zero error is negative if the pointer is above the zero mark. The number of divisions above the zero point should be subtracted from the reading.