Electromagnetic Induction (Doug G7 Ch21 Conceptual)

A flat coil is in a uniform magnetic field. The magnetic flux through the coil is greatest when the plane of its area is

• parallel to the magnetic field.

• at 45° with the magnetic field.

• perpendicular to the magnetic field.

According to Faraday's law, a coil in a strong magnetic field must have a greater induced emf in it than a coil in a weak magnetic field.

• True

• False

At a certain instant, coil A is in a 10-T external magnetic field and coil B is in a 1-T external magnetic field. Both coils have the same area and are oriented at right angles to the field. Which coil will have a greater emf induced in it?

• coil A

• coil B

• It is impossible to know without more information.

A coil of wire containing N turns is in an external magnetic field that is perpendicular to the plane of the coil and it steadily changing. Under these circumstances, an emf ε is induced in the coil. If the rate of change of the magnetic field and the number of turns in the coil are now doubled (but nothing else changes), what will be the induced emf in the coil?

• 2ε

• ε/2

• 4ε

• ε/4

• ε

According to Lenz's law, the induced current in a circuit always flows to oppose the external magnetic flux through the circuit.

• True

• False

Answer explanation

It flows in a direction that opposes the CHANGE in magnetic flux.

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the direction of the induced current in this coil as the field fades?

• The induced current flows counterclockwise.

• The induced current flows clockwise.

• There is no induced current in this coil.

• The current flows clockwise initially, and then it flows counterclockwise before stopping.

A coil lies flat on a level tabletop in a region where the magnetic field vector points straight up. The magnetic field suddenly grows stronger. When viewed from above, what is the direction of the induced current in this coil as the field increases?

• counterclockwise

• clockwise

• clockwise initially, then counterclockwise before stopping

• There is no induced current in this coil.

A coil lies flat on a horizontal tabletop in a region where the magnetic field points straight down. The magnetic field disappears suddenly. When viewed from above, what is the direction of the induced current in this coil as the field disappears?

• counterclockwise

• clockwise

• clockwise initially, counterclockwise before stopping

• There is no induced current in this coil.

Two solenoids are close to each other, with the switch S open. When the switch is suddenly closed, which way will the induced current flow through the galvanometer in the left-hand solenoid?

• from left to right

• from right to left

• There will be no induced current through the galvanometer.

An outer metal ring surrounds an inner metal ring. The current in the outer ring is counterclockwise and decreasing. What is the direction of the induced current in the inner ring?

• clockwise

• counterclockwise

• There is no induced current in the inner ring.