Concepts Of Physics MCQ Edition [Volume 2]PhysicsMagnetic Field due to a Current
A straight, current-carrying wire is positioned along the axis of a current-carrying circular loop. The straight wire
Options
- Awill exert zero force on the circular loop
- Bwill apply an outward force on the circular loop
- Cwill apply an inward force on the circular loop
- Dwill apply a force on the circular loop parallel to itself
Correct answer
A. will exert zero force on the circular loop
Step-by-step solution
Let the straight current-carrying wire be placed along the z-axis. The magnetic field produced by this wire at a distance r is given by B = ₀ I 2 r , which is tangential to any circle centered on the axis. The circular loop is centered on the axis, so its current elements d l are also directed along the tangential direction ( ). The magnetic force on a small current element of the loop is given by d F = I (d l B ) . Since both the current element d l and the magnetic field B are along the same line (parallel or ant