SAT Physics Subject Test

Chapter 12 Electromagnetic Induction

Chapter 12 Review Questions

See Chapter 17 for solutions.

  1. A metal rod of length L is pulled upward with constant velocity v through a uniform magnetic field B that points out of the plane of the page.

What is the potential difference between points a and b ?

(A) 0

(B) vBL, with point a at the higher potential

(C) vBL, with point b at the higher potential

(D) vBL, with point a at the higher potential

(E) vBL, with point b at the higher potential

  2. The circle and ellipse below have the same area.

If both loops are held so that their plane is perpendicular to a uniform magnetic field, B, how would ΦC, the magnetic flux through the circular loop, compare to ΦE, the magnetic flux through the elliptical loop?

(A) ΦC = 2.5ΦE

(B) ΦC =  ΦE

(C) ΦC = ΦE

(D) ΦE =  ΦC

(E) ΦE = 2.5ΦC

  3. The figure below shows a small circular loop of wire in the plane of a long, straight wire that carries a steady current I upward. If the loop is moved from distance x2 to distance x1 from the straight wire, what will be the direction of the induced current in the loop and the direction of the corresponding magnetic field it produces?

(A) The induced current will be clockwise, and the magnetic field it produces will point out of the plane of the page.

(B) The induced current will be clockwise, and the magnetic field it produces will point into the plane of the page.

(C) The induced current will be counterclockwise, and the magnetic field it produces will point out of the plane of the page.

(D) The induced current will be counterclockwise, and the magnetic field it produces will point into the plane of the page.

(E) None of the above

  4. A square loop of wire (side length = s) surrounds a long, straight wire such that the wire passes through the center of the square.

If the current in the wire is I, determine the current induced in the square loop.

(A) 

(B) 

(C) 

(D) 

(E) 0

  5. In the figure below, a permanent bar magnet is pulled upward with a constant velocity through a loop of wire.

Which of the following best describes the direction(s) of the current induced in the loop (looking down on the loop from above)?

(A) Always clockwise

(B) Always counterclockwise

(C) First clockwise, then counterclockwise

(D) First counterclockwise, then clockwise

(E) No current will be induced in the loop.

Keywords

electromagnetic induction

motional emf

magnetic flux

weber (wb)

Faraday’s law of electromagnetic induction

Lenz’s law

Summary

·        Motional emf refers to the effects on a wire or other conductor that moves relative to a uniform magnetic field. The action pushes electrons to the lower end of the wire, and leaves an excess of positive charge at the upper end. This separation of charges creates a uniform electric field within the wire.

·        Faraday’s law of electromagnetic induction states that the emf induced in a circuit is equal to the rate of change of the magnetic flux through the circuit. Use the equation εavg = – .

·        Magnetic flux measures the density of magnetic field lines that cross through an area. The magnetic flux (ΦB) through an area A is equal to the product of A and the magnetic field perpendicular to it. Use the equation ΦB = B  ABA cos θ.

·        Lenz’s law states that the induced current will always flow in the direction that opposes the change in magnetic flux that produced it. If Lenz’s law were not true, then the system would be in violation of the law of conservation of energy.