Exams › JEE Main › Physics

A meter-bridge whose wire has total resistance R0 = 50 Ohm is used to measure the internal resistance r1 of a cell of emf E. The circuit also contains a fixed resistance R0/2, a second driver cell of emf E/2 (internal resistance r) and a galvanometer G, connected as shown. If the balance (null) point on the bridge wire is obtained at length l = 72 cm (out of 100 cm), what is the internal resistance r1 of the first cell?

1. 3 Ohm
2. 6 Ohm
3. 9 Ohm
4. 12 Ohm

Correct answer: 3 Ohm

Solution

This is the JEE Advanced 2014 meter-bridge problem. The driver cell E/2 drives current through the series combination R0/2 + R0 (the bridge wire), and the balance length picks off a potential that must equal the emf-side balance of the unknown cell branch. Solving the balance condition with R0 = 50 Ohm and l = 72 cm gives r1 = 3 Ohm.

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 →