Magnetic Induction Exam 3

How much does the energy stored in an inductor change if the current through the inductor is doubled?

it is quadrupled

A long narrow solenoid has length E and a total of N turns, each of which has cross-sectional area A. Its inductance is:

μ0N^2A/E

A solenoid is 15 cm long, has a radius of 5 cm, and has 400 turns. If it carries a current of 4 A, the magnetic energy stored in the solenoid is

84.2 mJ

A long straight wire carries a constant current I. The magnitude of the magnetic flux through the illustrated rectangular loop of wire is

(μ0/4π)2Il ln(b/a)

A wire rod rolls with a speed of 20 m/s on two metallic rails, 1.0 m apart, that form a closed loop. If the magnetic field is 1.5 T into the page, the power dissipated in the resistor R and the current direction are, respectively,

76 mW, clockwise.

For the two solenoids above, if l = 50 cm, N1 = N2 = 200 turns and r1 = 5 cm and r2 = 10 cm, the mutual inductance of the two solenoids

0.790 mH

A wire rod rolls with a speed of 8.0 m/s on two metallic rails, 30 cm apart, that form a closed loop. A uniform magnetic field of magnitude 1.20 T is into the page. The magnitude and direction of the current induced in the resistor R are

0.82 mA, counterclockwise.

A cylindrical region of radius R contains a uniform magnetic field, parallel to its axis, with magnitude that is changing linearly with time. If r is the radial distance from the cylinder axis, the magnitude of the induced electric field outside the cylinder is proportional to:

1/r

A wire rod rolls with a speed of 30 m/s on two metallic rails, 2.0 m apart, that form a closed loop. The magnetic field is 2.6 T. The power dissipated in the resistor R and the current direction are, respectively,

2.0 W, clockwise.

A circular loop of radius 25 cm is sitting in a perpendicular magnetic field of 0.2 T. If the magnetic field strength changes to a value of 0.5 T in 2.5 s, calculate the induced EMF in the loop.

2.4 × 10-2 V

A circular loop of radius R has 50 turns. It lies in the xy plane. A time dependent magnetic field where A is a constant, passes through the loop. The EMF induced in the loop is

50πωAR2 cos (ωt)

You place a coil that has 200 turns and a cross-sectional area of 0.050 m2 so that its plane is normal to a field of 3.0 T. If the field is uniformly decreased to zero in 5.0 s, what EMF is induced in the coil?

6.0 V

Eddy currents

All of these are correct.

A motor sometimes burns out when its load is suddenly increased because the resulting sudden decrease in its rotational frequency causes

B. a decreased back EMF and an increased current flow.

The emf that appears in Faraday's law is:

B. around the boundary of the surface used to compute the magnetic flux

A square loop of wire lies in the plane of the page. A decreasing magnetic field is directed into the page. The induced current in the loop is:

B. clockwise

A cylindrical region of radius R contains a uniform magnetic field, parallel to its axis, with magnitude that is changing linearly with time. If r is the radial distance from the cylinder axis, the magnitude of the induced electric field inside the cylinder is proportional to:

B. r

The emf developed in a coil X due to the current in a neighboring coil Y is proportional to the:

B. rate of change of magnetic field in X

The figure shows a bar moving to the right on two conducting rails. To make an induced current i in the direction indicated, a constant magnetic field in region A should be in what direction?

C. Into the page

A long straight wire is in the plane of a rectangular conducting loop. The straight wire carries an increasing current in the direction shown. The current in the rectangle is:

C. counterclockwise

You push a permanent magnet with its north pole away from you toward a loop of conducting wire in front of you. Before the north pole enters the loop the current in the loop is:

C. counterclockwise

A rod lies across frictionless rails in a uniform magnetic field B, as shown. The rod moves to the right with speed v. In order for the emf around the circuit to be zero, the magnitude of the magnetic field should:

C. decrease linearly with time

Faraday's law states that an induced emf is proportional to:

C. the rate of change of the magnetic flux

A long straight wire is in the plane of a rectangular conducting loop. The straight wire initially carries a constant current i in the direction shown. While the current i is being shut off, the current in the rectangle is:

Clockwise

A long straight wire is in the plane of a rectangular conducting loop. The straight wire carries a constant current i, as shown. While the wire is being moved toward the rectangle the current in the rectangle is:

Counterclockwise

A rod with resistance R lies across frictionless conducting rails in a constant uniform magnetic field B, as shown. Assume the rails have negligible resistance. The magnitude of the force that must be applied by a person to pull the rod to the right at constant speed v is:

D. B2L2v/R

The diagram shows an inductor that is part of a circuit. The direction of the emf induced in the inductor is indicated. Which of the following is possible?

D. The current is increasing and leftward

If the magnetic flux through a certain region is changing with time:

D. an emf must exist around the boundary

In the circuit shown, there will be a non-zero reading in galvanometer G:

E. only just after S is opened or closed

For the current in a stationary circuit to induce a current in an independent stationary circuit, it is necessary for the first circuit to have

a changing current.

A device used chiefly for storing energy in a magnetic field is

an inductor.

The instantaneous induced EMF in a coil of wire located in a magnetic field

depends on the time rate of change of flux through the coil.

A copper ring lies in the yz plane as shown. The magnet's long axis lies along the x axis. Induced current flows through the ring as indicated. The magnet

must be moving toward the ring.

A cylindrical region of radius R contains a uniform magnetic field parallel to its axis. The field is zero outside the cylinder. If the magnitude of the field is changing at the rate dB/dt, the electric field induced at a point 2R from the cylinder axis is:

not 2R dB /dt (R/2) dB /dt

After you measure the self-inductance of a coil, you unwind it and then rewind half the length of wire into a coil with the same diameter but half the number of turns. How does this change the self-inductance?

not it is doubled it is halved