Exams › JEE Advanced › Physics

A bar magnet lies in front of a coil. The line joining the centre of the magnet to the centre of the coil (the central axis) is perpendicular to the plane of the coil. Which of the following motions of the magnet will NOT induce a current in the coil?

1. Translational motion back and forth along the central axis.
2. Translational motion up and down (perpendicular to the central axis).
3. The magnet's axis is tilted to the central axis and the magnet spins about the central axis.
4. The magnet's axis swings back and forth about the central axis within the plane of the paper.

Correct answer: The magnet's axis is tilted to the central axis and the magnet spins about the central axis.

Solution

EMF is induced only when the flux through the coil changes. If the magnet is tilted at a fixed angle to the central axis and merely spins about that axis, the geometry relative to the coil (and hence the flux through it) stays constant in time, so no EMF and no current. Back-and-forth translation, up-and-down translation, and swinging all change the flux, so they induce current.

Related JEE Advanced Physics questions

• What is the final velocity attained by the loop?
• A long coaxial cable is made up of two cylindrical conductors with radii a and b. The inner conductor carries a constant current i, while the outer conductor acts as the return path for the current. What is the self-inductance of a segment of the cable of length l?
• Determine the inductance per unit length for a loop created by connecting the ends of two infinitely long parallel wires, each with radius r, and separated by a distance d between their centers. Ignore the magnetic flux inside the wires and the effects at the ends.
• If the electromotive force is 10 V and the rate of change of current is calculated as 2.5 A/s, what is the self-inductance of the coil, given by L = e / (dl/dt)?
• The magnitude of the induced electric field in the orbit at any instant of time during the time interval of the magnetic field change is
• A semicircular loop of radius r is positioned on the axis of a large current-carrying circular ring of radius R (with R >> r). The loop is placed at an axial distance of R*sqrt(3) from the center of the ring, and the plane of the semicircular loop makes an angle of 53 deg with the plane of the ring. Find the mutual inductance M between the two coils.

⚔️ Practice JEE Advanced Physics free + battle 1v1 →