Electromagnetic Induction – Motional EMF and Eddy Current: NEET MCQs with Answers

A straight rod of length l moves without rotating, at speed v, in a plane perpendicular to a uniform magnetic field B. In case (a) the velocity makes an angle θ with the rod. In case (b) the velocity makes an angle θ with the normal to the rod, drawn in the same plane. In case (c) the velocity is directed along the rod. What are the emfs induced across the rod in cases (a), (b) and (c), in that order?

A rod of length l slides at a constant speed v on two smooth parallel conducting rails joined at one end through a resistance R, in a uniform magnetic field B perpendicular to the plane of the rails. All other resistance is negligible. If different steady speeds are tried, how do the induced emf ε, the applied force F and the mechanical power P supplied depend on v?

A metal rod 25 cm long lies across two parallel conducting rails in a uniform 0.40 T magnetic field perpendicular to the plane of the rails. An external agent keeps the rod moving along the rails at a steady 10 cm/s, and the closed circuit has a total resistance of 5.0 mΩ. At what rate is heat produced in the circuit?

A metal rod 0.5 m long lies north-south and slides east at a steady 4 m/s through a uniform 0.25 T magnetic field directed vertically downward. The rod is not part of any circuit. Once the free electrons have stopped drifting along the rod, which description is correct?

A straight metal rod 40 cm long lies along the y-axis and moves at 5 m/s along +x in a uniform magnetic field of 0.2 T along +z. The rod is not part of a closed circuit. Once charges have stopped shifting along the rod, what is the electric field inside it, and which end is positive?

A square wire loop of side 0.4 m and resistance 2 Ω lies wholly inside a uniform magnetic field of 0.5 T, with its plane perpendicular to the field. It is pulled out at a steady speed through the straight edge of the field, with one side of the loop parallel to that edge. What is the work done by the pulling force if the loop is taken out completely in (i) 0.1 s and (ii) 0.4 s?

A conducting ring of radius 5 cm translates in its own plane at 2 m/s, without rotating, in a uniform 0.4 T magnetic field perpendicular to that plane. A is the foremost point of the ring in the direction of motion, and C is a point on the ring 90° around from A. What are the magnitude of the potential difference between A and C and the net emf around the whole ring?

A straight rod slides on two smooth parallel conducting rails 0.4 m apart, which are joined at one end through a 0.2 Ω resistor. All other resistance is negligible, and a 0.5 T uniform magnetic field is perpendicular to the plane of the rails. What mechanical power must an external agent supply to keep the rod moving at a steady 10 m/s?

Two parallel conducting rails lie along the x-direction in the xy-plane, and a rod of length l lying along y slides on them at speed v along +x. A uniform magnetic field of magnitude B is applied in turn along (a) the x-axis, (b) the y-axis and (c) the z-axis. The emf induced in the rod in the three cases, in that order, is

A metal rod moves on frictionless parallel rails in a uniform magnetic field perpendicular to the plane of the rails. The circuit joining the rails contains a switch, which is kept open. Statement I: An emf exists across the rod while it moves. Statement II: No external force is needed to keep the rod moving at constant velocity.

A metal rod of length 20 cm slides without friction on two parallel conducting rails, staying perpendicular to them, in a uniform magnetic field of 0.40 T perpendicular to the plane of the rails. The closed circuit has a total resistance of 5.0 mΩ. What mechanical power must an external agent supply to keep the rod moving at a steady 25 cm/s?

A metal rod of length 0.5 m and resistance 2 Ω rotates at 100 rad/s about one end, at the centre of a circular metal ring of radius 0.5 m, with its free end sliding on the ring. A uniform field of 0.4 T acts perpendicular to the plane of the ring. The centre and the ring are joined by a wire of negligible resistance, and the ring also has negligible resistance. The power dissipated is:

A square conducting loop of side 20 cm lies in the xy-plane with its sides parallel to the axes. It moves at a constant 5 cm/s along +x through a magnetic field that points along +z everywhere. The field does not depend on time or on y, but it increases steadily by 2 × 10⁻³ T per cm as one moves along −x. The magnitude of the emf induced in the loop is:

A rod of length 0.5 m slides at a constant 5 m/s along two parallel frictionless conducting rails joined at one end. The plane of the rails is perpendicular to a uniform field of 0.4 T, and the total circuit resistance is 2 Ω, which stays constant. What external force keeps the speed constant, and at what rate does this force do work?

A straight metal rod 1.2 m long rotates in a horizontal plane at 3 revolutions per second about a vertical axis through its midpoint. A uniform vertical magnetic field of 5 × 10⁻⁵ T is present. What are the magnitudes of the emf between the midpoint and one end, and of the emf between the two ends? (Take π = 3.14)