JEE Main202628 January 2026Morning ShiftPhysicsMagnetic Effects of CurrentActual
Three long straight wires carrying current are arranged mutually parallel as shown in the figure. The force experienced by 15 cm length of wire Q is _ _ _ _ . ( _ o =4 10⁻⁷ ~T . m / A )
Options
- A6 10⁻⁶ ~N towards P
- B6 10⁻⁷ ~N towards P
- C6 10⁻⁷ ~N towards R
- D6 10⁻⁶ ~N towards R
Correct answer
D. 6 10⁻⁶ ~N towards R
Step-by-step solution
The force per unit length between parallel wires is F/L = ₀ I₁ I₂ 2 d . Force on Q from P (opposite currents, repulsive towards R): F_ QP L = 4 10⁻⁷ 3 1 2 0.03 = 2 10⁻⁵ N/m. Force on Q from R (same currents, attractive towards R): F_ QR L = 4 10⁻⁷ 1 2 2 0.02 = 2 10⁻⁵ N/m. Total force per unit length towards R: 4 10⁻⁵ N/m. For 0.15 m length: F = 4 10⁻⁵ 0.15 = 6 10⁻⁶ N towards R.