Exams › JEE Main › Physics

Two metal wires having the same length and same cross-sectional area are joined in series. If their conductivities are sigma1 and sigma2, what is the effective conductivity of the series combination?

1. sigma1 sigma2 / (sigma1 + sigma2)
2. 2 sigma1 sigma2 / (sigma1 + sigma2)
3. (sigma1 + sigma2) / (2 sigma1 sigma2)
4. (sigma1 + sigma2) / (sigma1 sigma2)

Correct answer: 2 sigma1 sigma2 / (sigma1 + sigma2)

Solution

Adding the two equal-length resistances and equating to one wire of double length gives the harmonic-type result 2 sigma1 sigma2 / (sigma1 + sigma2).

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 →