Question

consider the scale of a voltmeter shown in the diagram and answer the following questions a. what is the least count of voltmeter, b. what is the reading shown by the voltmeter,. if this voltmeter is connected across a resistor of 20ohm how much current is flowing through the resistor
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Answer 1

solution : (a) least count of voltmeter = range/number of divisions on voltmeter scale

here, range = (1.5 - 0)= (3.0 - 1.5)= 1.5

number of divisions on voltmeter scale = 10

so, least count of voltmeter = 1.5/10 = 0.15

(b) reason of voltmeter = main scale + n × least count

here, main scale = 1.5V , n = 2 and least count = 0.15

so, reading of voltmeter = 1.5 + 2 × 0.15

= 1.5 + 0.3 = 1.8V

(c) reading of voltmeter is 1.8V

resistance of resistor is 20 ohms.

from Ohm's law,

V = IR => I = V/R = 1.8/20 = 0.09A

Answer 2

Answer:

LC of ammeter =  0.2 / 10

= > 0.02 A

A = 0.02 A

LC of Voltmeter =  1 / 10

= > 0.1 V

V = 0.1 V

Current = 15 x 0.02 A = 0.3 A

Potential difference = 21 x 0.1 V = 2.1 V