PHY 204 Quiz 4

Complete the following sentence: The phenomenon of producing an induced emf with the aid of a magnetic field is

• called electromotive production.

• almost never observed.

• a scientific curiosity with no practical application.

• only produced by changing the magnetic field in the presence of a coil of wire.

• called electromagnetic induction.

Which of the following phrases best describe the term magnetic flux?

• the direction of the magnetic field relative to a surface

• the amount of magnetic field that passes through a surface

• the number of magnetic dipoles moving through a wire

• the flow of magnetons in space

• Choice (a) and (b) are both correct.

The plane of a conducting loop is oriented parallel to the x-y plane. A magnetic field is directed in the -z direction. Which one of the following actions will not change the magnetic flux through the loop?

• Decrease the area of the loop

• Decrease the strength of the magnetic field.

• Increase the strength of the magnetic field.

• Rotate the loop about an axis that is directed in the z direction and that passes through the center of the loop.

• Rotate the loop about an axis that is directed in the y direction and that passes through the center of the loop.

A conducting bar slides with a velocity v to the right on some conducting rails as shown. A uniform magnetic field is directed perpendicular to the bar. Answer the following two questions: (1) Will the light bulb “turn on” in this case? and (2) How is the magnetic flux through the conducting loop changing, if at all, as the bar slides to the right?

• no, the magnetic flux remains constant

• yes, the magnetic flux decreases

• no, the magnetic flux increases

• yes, the magnetic flux increases

• yes, the magnetic flux remains constant

Which of the following choices is the SI unit for magnetic flux?

• gauss (G)

• tesla (T)

• weber (Wb)

• Lumen (L)

• Fluxon (Fl)

Which of the flowing expressions equals the magnetic flux?

• BA cos φ

• BAcos² φ/

• BA sin²φ

• B/A

• µ₀IBA

A coil of wire with N turns and area A is placed into a magnetic field of magnitude B. The angle of the normal to the plane of the coil is at an angle φ with respect to the magnetic field. According the Faraday’s law, which of the following changes will produce an emf in a coil of wire?

• B is decreased

• A is increased

• φ is decreased

• any of the above choices

• none of the above choices

Complete the following statement: Lenz’s law indicates that induced currents form to oppose

• a change in the magnetic field direction.

• a change in the magnetic field

• the magnetic flux.

• a change in the electric flux

• a change in the magnetic flux.

Which one of the following actions will not result in an induced current?

• Drop a magnet through a closed metal ring

• Move a metal loop away from a current carrying wire.

• Drop an iron sheet through a region with a constant magnetic field.

• Hold a copper loop next to a current carrying wire

• All of the above choices result in an induced current.

An ammeter is connected to a coil of wire. A magnet is sitting motionless next to the wire such that its south end is near the coil and perpendicular to the plane of the coil as shown. The meter indicates that a current is flowing through the wire from the left toward the right. What, if anything, is wrong with this picture?

• The current should be flowing from the right toward the left

• The needle should be slanted toward the right.

• The needle should indicate that there is no current flowing.

• There is nothing wrong with the picture.