Question

Consider the scale of a voltmeter shown in the diagram and answer the following questions :

i) what is the least count of the voltmeter?

ii) what is the reading shown by the voltmeter?

iii) if this voltmetre is connected across a resistor of 20 Ω, how much current is flowing through the resistor? ​

Answer 1

Answer:

i) 0.5 volts is the least count of the voltmeter

ii)  As Voltmeter is considered to be open circuit ideally, there would be no current passing through it. So 2A current passes through all the resisters giving voltage drop across each resisters as V = IR

Explanation:

Answer 2

The least count is 0.15V, the current voltmeter reading is 1.8V and the current across the resistor is 0.09A.

1. Least count of the given voltmeter is 0.15V.

Least Count :

• The Least Count of any tool is the smallest measurement of value that can be measured using that tool.
• Thus, it is the measurement of the smallest division in the scale of that tool

Here, the total measurement that can be measured = 3.0 V

Number of divisions in total = 20

Thus, Least count = Measurement of 1 division

                              $= 3.0V/20$

                              $= 0.15 V$

2. The reading of the given voltmeter is 1.8V.

The reading can be calculated using the main scale reading and the sub-scale reading.

Here, the main scale reading is 1.5 as the arrow position is after that.

The sub-scale reading has 2 divisions more than the main scale reading. Thus, the actual reading is :

                      = Main Scale Reading + (2* Least Count)

                      $= 1.5V + (2*0.15V)$

                      $= 1.5V + 0.3V$

                      $= 1.8V$

3. The current flowing through the given resistance according to the voltmeter reading is 0.09 Amperes.

The formula for Potential difference V, electric current I, and the resistance R is given as :  

                          $V = I * R$

                          $1.8 = I * 20$

                          $I = 1.8/20$

                          $I = 0.09A$

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