Exams › JEE Main › Physics

If the current through a resistor of uniform cross-section is doubled (temperature kept essentially constant), which of the following statements is INCORRECT?

1. the conduction electron density is doubled
2. the current density is doubled
3. the mean time between collisions stays the same
4. the electron drift speed is doubled

Correct answer: the conduction electron density is doubled

Solution

Carrier (electron) density n is a fixed property of the conductor and does not change with current; doubling I doubles current density and drift speed, but n stays constant, so that statement is incorrect.

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 →