Exams › JEE Main › Physics

A potentiometer wire AB is 400 cm long and has a resistance per unit length r = 0.01 Ohm/cm. A driver cell of EMF 2 V (negligible internal resistance) is connected across the full length of the wire. An ideal voltmeter is connected between end A and a jockey J placed at 50 cm from A. What is the reading of the voltmeter?

1. 0.20 V
2. 0.25 V
3. 0.75 V
4. 0.50 V

Correct answer: 0.25 V

Solution

With an ideal voltmeter (infinite resistance), no current is diverted, so the potential gradient along the wire is uniform. The voltmeter between A and J simply reads the fraction of the driver voltage corresponding to the AJ length.

Related JEE Main Physics questions

• A physical quantity X is defined as ε0L(ΔV/Δt), where ε0 denotes the permittivity of free space, L is a length, ΔV is a potential difference, and Δt is a time interval. The dimensional formula of X matches that of which of the following?
• A set of n identical resistors is arranged once in a series combination and once in a parallel combination. What is the ratio of the larger equivalent resistance to the smaller equivalent resistance?
• A resistance coil is connected to a battery. In which arrangement will the maximum heat be produced?
• A bulb is rated at 220 V and 100 W. If the applied voltage falls by 2.5% from its rated value, by what percentage of the rated power will the power output decrease?
• An ammeter has a coil resistance of R. To extend its measuring range by a factor of n, the shunt resistance needed should be:
• How does the drift velocity Vd depend on the strength of the applied electric field?

⚔️ Practice JEE Main Physics free + battle 1v1 →