Exams › JEE Main › Physics

A copper wire has a cross-sectional area of 5 mm² and carries a current of 1.5 A. If the electron number density in copper is 9 × 10²⁸ m⁻³, the drift speed of the electrons is v. Taking the electron charge as 1.6 × 10⁻¹⁹ C, the value of v in mm/s is approximately:

1. 0.02
2. 3
3. 2
4. 0.2

Correct answer: 0.02

Solution

The drift speed of electrons can be calculated using the formula v = I / (n * A * e), where I is the current, n is the electron number density, A is the cross-sectional area, and e is the charge of an electron. Substituting the given values results in a drift speed of approximately 0.02 mm/s, confirming that option A is correct.

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 →