Electromagnetic Induction

A conducting loop is pulled away from a long straight wire carrying a steady current I. The plane of the loop is perpendicular to the wire, and the loop remains parallel to itself during the motion. The induced current in the loop is such that it

1. Produces a magnetic field in the same direction as the field due to the wire through the loop.
2. Produces a magnetic field opposite to the field due to the wire through the loop.
3. Is always clockwise irrespective of the direction of current in the wire.
4. Is always zero because the current in the wire is constant.

A copper plate swings like a pendulum between the poles of a strong magnet. After a few oscillations, it comes to rest much sooner than it would without the magnet. The damping is primarily due to

1. Electrostatic attraction between the plate and the magnet.
2. Eddy currents induced in the plate.
3. Magnetic induction changing the mass of the plate.
4. Self-induction in the supporting string.

A coil of inductance L carries a steady current I. The battery is suddenly disconnected, and the coil is connected across a small neon bulb. The bulb flashes because

1. The current instantly becomes zero, producing a large magnetic force.
2. The collapsing magnetic field induces a large emf across the coil.
3. The inductor stores electric charge like a capacitor.
4. The battery leaves behind a residual voltage equal to its emf.

A metal disc rotates with angular speed ω about its center in a uniform magnetic field directed perpendicular to the plane of the disc. The emf between the center and the rim is E. If both the radius of the disc and the angular speed are doubled, the new emf becomes

1. 2E
2. 4E
3. 8E
4. 16E

A conducting rod of length L slides without friction on two parallel conducting rails inclined at an angle θ to the horizontal. A uniform magnetic field B acts vertically upward. The rod moves down the incline with speed v. The induced emf across the rod is proportional to

1. BLv
2. BLv cos θ
3. BLv sin θ
4. BLv tan θ

An inductor is connected in series with a resistor and an ideal battery. After a long time, the circuit reaches steady state. Which statement is correct?

1. The inductor behaves like an open circuit because it opposes current.
2. The inductor behaves like a short circuit because the current is no longer changing.
3. The induced emf in the inductor equals the battery emf forever.
4. The current through the resistor becomes zero because all voltage appears across the inductor.

A long solenoid carries a steadily increasing current. A small closed conducting loop is placed completely outside the solenoid, close to its surface. Which statement is correct?

1. No emf is induced because the magnetic field outside an ideal solenoid is zero.
2. An emf is induced because the magnetic flux linked with the loop changes.
3. Current is induced only if the loop touches the solenoid.
4. The induced emf depends only on the resistance of the loop.

Two identical conducting loops are placed in the same changing magnetic field. Loop P has twice the electrical resistance of Loop Q. Which statement is correct?

1. The induced emf in Loop P is twice that in Loop Q.
2. The induced current in Loop P is half that in Loop Q.
3. Both induced emf and current are the same in the two loops.
4. The induced current is independent of resistance because both loops experience the same changing flux.

A coil is connected to a battery through a switch. Immediately after the switch is closed, the current begins to increase. The induced emf due to self-induction acts in such a direction that it

1. Increases the current in the coil.
2. Opposes the increase in current.
3. Opposes the battery voltage permanently, making the current zero.
4. Has no effect because the battery is an external source.

A conducting square loop is rotated with constant angular speed in a uniform magnetic field about an axis passing through its center and lying in the plane of the loop. Initially, the plane of the loop is perpendicular to the magnetic field. At the instant when the magnetic flux through the loop is maximum, the induced emf is

1. Maximum
2. Minimum but non-zero
3. Zero
4. Equal to half of its maximum value

A coil of negligible resistance is connected across the terminals of an ideal voltmeter. A bar magnet is held stationary near the coil. Which action will produce the largest voltmeter reading?

1. Keeping the magnet stationary for a longer time.
2. Rotating the magnet rapidly about its own magnetic axis while keeping its center fixed.
3. Moving the magnet quickly toward the coil and then stopping it.
4. Increasing the strength of the stationary magnet without changing the magnetic flux through the coil.

A bar magnet is dropped vertically through a horizontal conducting ring. Air resistance is negligible. Which statement correctly describes the motion of the magnet?

1. The ring always attracts the magnet during its motion.
2. The ring always repels the magnet during its motion.
3. The ring opposes the magnet's motion during both entry and exit.
4. The ring has no effect because the magnet is moving freely.

A rectangular conducting loop is moving with constant velocity through a large region of uniform magnetic field. The plane of the loop remains perpendicular to the field at all times. During the interval when the entire loop is completely inside the magnetic field, the induced emf is

1. Maximum.
2. Zero.
3. Constant but non-zero.
4. Increasing continuously.

A conducting rod moves with constant velocity perpendicular to a uniform magnetic field and also perpendicular to its own length. The rod forms part of a closed conducting circuit. If the speed of the rod is doubled while the magnetic field strength is halved, the induced current in the circuit will

1. Double.
2. Become half.
3. Remain unchanged.
4. Become zero.

A circular conducting loop is placed in a uniform magnetic field directed into the plane of the paper. The magnitude of the magnetic field is increasing uniformly with time. A second identical loop is placed beside it in the same field, but a narrow slit is cut in the second loop, making it an open circuit. Which statement is correct?

1. Both loops develop induced current in the same direction.
2. Only the closed loop develops induced current, but both loops have induced emf.
3. Only the open loop develops induced emf because current cannot flow.
4. Neither loop develops emf because the magnetic field is uniform.