JEE Main 2025 Jan 29 Shift 2, Physics Q3: Coulomb's Law And Electric Field

JEE Main2025Jan 29, Shift 2Physics

An electric dipole is placed at a distance of $2$ cm from an infinite plane sheet having positive charge density $σ_{0}$ . Choose the correct option from the following.

A
Torque on dipole is zero and net force is directed away from the sheet.
B
Torque on dipole is zero and net force acts towards the sheet.
C
Potential energy of dipole is minimum and torque is zero.
D
Potential energy and torque both are maximum

Solution

The field of an infinite charged sheet is uniform: $E = \frac{σ _{0}}{2 ε _{0}} \overset{n}{^}$ , pointing away from the sheet.

From the figure the dipole moment $p$ (from $- q$ to $+ q$ ) also points away from the sheet, i.e. parallel to $E$ .

Torque: $τ = p \times E = 0$ (parallel vectors).

Potential energy: $U = - p \cdot E = - pE$ , which is the minimum value of $- pE cos θ$ over all orientations.

Net force in a uniform field is zero, so options (1) and (2) are wrong.

$∴$ Option (3) is correct.

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JEE Main 2025 Jan 29 Shift 2, Physics Q3: Coulomb's Law And Electric Field

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