# A voltmeter of resistance 400 Ω is used to measure the potential difference across the 100Ω resistor in the circuit shown in figure.(a) What will be the reading of the voltmeter?(b) What was the potential difference across 100Ω before the voltmeter was connected? Concepts/Formula used:
Resistors in Series: Resistors in parallel: Ohm’s Law:

Potential Difference (V) across a resistor of resistance R when current I passes through it is given by Ohm’s law: (a)

The given circuit is: We can easily see that the voltmeter and R1 are in parallel. The equivalent resistance, r’ is given by:  We can redraw the circuit as follows: Note that r’ and R2 are in series. The equivalent resistance is given by: The current coming out of the battery also passes through r’. By Ohm’s law,  Now, the voltmeter reads the potential different across R1 .  (b)

The given circuit is now: The equivalent resistance is : The current is the same throughout the circuit as all components are in series and is given by:  Now, the potential difference across R1 is given by:   Hence, the potential difference across the 100Ω resistor before connecting the voltmeter was 28V.

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Related Videos  Electrostatics of Conductors50 mins  Electric Dipole46 mins  Electric field inside cavity37 mins  Electric Flux - Theory46 mins  Electric Charges and Fields - 0556 mins  Test Your Knowledge of Electric Charge & Coulomb's Law47 mins  Check your knowledge of Electric Potential | Quiz45 mins  Electric Charges and Fields - 0352 mins  Electric Charges and Fields - 0155 mins  Electric Charges and Fields - 0946 mins
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation view all courses 