Question

The reading of voltmeter in the circuit shown is

• A. 2.25 V
• B. 3.25 V
• C. 4.25V
• D. 6.25V

Hint:

The potential difference across each resistor in a parallel combination of resistance is the same.

Answer 1

The Correct Option is A

The correct answer is Option A) 2.25 V

From the figure, the resistance of 60 \(\Omega\) of the resistor and resistance 40 \(\Omega\)  of the voltmeter are in parallel.

 Therefore the equivalent resistance of these two resistances in parallel is given by

R_eq \(=\frac{60\times40}{60+40}=\frac{60\times40}{100}=24\,\Omega\) 

The total current in the circuit is given by,

I \(=\frac{6\,V}{\left(40+24\right)\,\Omega}=\frac{6}{64}=\frac{3}{32}\,A\) 

The voltmeter reads potential differences across the resistance 60 \(\Omega\) connected in parallel to it. Therefore using Ohm's law, the potential across the voltmeter is given by

 \(\therefore\quad\) Voltmeter reading = \(I\times R_{eq}\) \(=\frac{3}{32}\times24=\frac{9}{4}V=2.25\,V\)

Discover More from Chapter: Current Electricity

Answer 2

The correct answer is Option A) 2.25 V

Real Life Applications

1. Voltmeters can be used to check the voltage of batteries to see if they are still good. 
2. Voltmeters can be used to troubleshoot electrical circuits to find the source of a problem. 
3. Voltmeters can be used to calibrate other instruments, such as ammeters and ohmmeters. 
4. Voltmeters are used in research to measure the voltage of different devices and materials.

Question can also be asked as

1. What is the voltage reading across 60Ω in the circuit shown? 
2. What is the potential difference across 60Ω in the circuit shown? 
3. What is the reading of the voltmeter in the circuit shown? 
4. How much voltage is measured across 60Ω in the circuit shown? 

Answer 3

The correct answer is Option A) 2.25 V

The equivalent resistance of the combination of resistors is defined as a single resistor on which the same current flows as the given combination of resistors whether in series or parallel combination, when the same potential difference is applied across its ends.

Equivalent Resistance in Series Combination of Resistors

• The formula for equivalent resistance for two or more resistors in series is given by \(R_{eq}=R_1+R_2+R_3+.........\)
• In a series combination of resistors, the current flow through all resistors is the same, when the potential difference across the combination is the same.

Equivalent Resistance in Parallel Combination of Resistors

• The formula for equivalent resistance for two or more resistance connected in parallel is given by \(\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+.........\)
• For the resistors connected in parallel, the potential difference across each resistance is the same and is equal to the applied potential across the combination.

Ohm's Law

• According to Ohm's law, if the physical condition like temperature, pressure, etc. remains the same then the current flowing through the conductor is directly proportional to the potential difference across its two ends.
• The formula of Ohm's law is \(V=IR\).

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