Question 1

FIGURE 29-11 
-A cube whose edges are 0.10 m long has one corner at the origin of an xyz-coordinate system as shown in Fig. 29-11. A magnetic field with a strength of 0.40 T is applied along the +x-axis.
(a) What is the magnetic flux through the shaded face of the cube?
(b) What is the magnetic flux through the face of the cube along the yz plane at x = 0?
(c) What is the total magnetic flux through the six faces of the cube?

Accepted Answer

The answer of FIGURE 29-11 
-A cube whose edges are...

Question 2

FIGURE 29-5 -The two identical bar magnets in Fig. 29-5 are dropped from rest along a vertical line passing through the center of the rings, as shown. The two rings are identical in every respect except that the ring on the right has a small break in it. Calling a_L and a_R the magnitude of the downward accelerations of the magnets on the left and right, respectively, you observe that

Accepted Answer

The ring on the left will experience an induced current due to the changing magnetic field as the magnet falls, creating a magnetic field that opposes the motion of the magnet (Lenz's Law), thus reducing its acceleration. The ring on the right, being broken, cannot sustain an induced current, so the magnet falls with acceleration closer to free fall.

Question 3

FIGURE 29-10 
-A rectangular coil with N turns, length L, and width w, as shown in Fig. 29-10, is rotating in a magnetic field B with an angular frequency ω. If the area of the coil is A, what is the induced emf in the coil?

Accepted Answer

The induced emf in a rotating coil is given by the equation ε = NBAω sin ωt, where N is the number of turns in the coil, B is the magnetic field strength, A is the area of the coil, and ω is the angular frequency of rotation. All of the answer choices are correct because they all represent different forms of this equation.

Question 4

A transformer is a device used to

Accepted Answer

A transformer is a device that can increase or decrease the voltage of an alternating current. It does not work with direct current as DC cannot be easily transformed using a transformer. Therefore, option A and D are incorrect. Additionally, a transformer does not convert AC to DC or vice versa, making option B incorrect as well.

Question 5

FIGURE 29-3 
-Fig. 29-3 above shows a bar magnet moving upward along the vertical axis toward a horizontal coil. The poles of the bar magnets are labeled X and Y. As the bar magnet approaches the coil it induces an electric current in the direction indicated on the figure. What are the correct polarities of the magnet?

Accepted Answer

The correct answer is A because the induced current in the coil is in the clockwise direction, which means that the magnetic field produced by the coil is in the upward direction. This means that the pole of the magnet that is closest to the coil must be a south pole, and the pole of the magnet that is farthest from the coil must be a north pole.

Question 6

FIGURE 29-6 
-A metallic rod moves at constant speed in the positive x direction inside a uniform magnetic field as shown in Fig. 29-6. Positive and negative charges build up on the rod as indicated. What is the direction of the magnetic field?

Accepted Answer

The answer of FIGURE 29-6 
-A metallic rod moves at...

Question 7

FIGURE 29-7 
-Fig. 29-7 shows 3 metallic frames labeled A, B, and C heading towards a region where a uniform magnetic field exists. The frames move with the same constant velocity. Their relative sizes are indicated by the background grid. As they enter the magnetic field the frames will have an induced electric current along their perimeter. For which frame will the current be the greatest?

Accepted Answer

The answer of FIGURE 29-7 
-Fig. 29-7 shows 3 metallic...

Question 8

FIGURE 29-10 
-A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be a maximum?

Accepted Answer

The induced emf is maximized when the plane of the loop is perpendicular to the magnetic field lines. For a uniform magnetic field pointing straight down, any horizontal orientation of the loop's axis of rotation will ensure that the plane of the loop is perpendicular to the field lines at some point during the rotation, maximizing the change in magnetic flux and thus the induced emf.

Question 9

Generators that were used in the past to supply electricity in automobiles have been replaced by

Accepted Answer

Alternators have replaced generators in automobiles because they are more efficient and can produce more power at lower engine speeds.

Question 10

Electric power is transmitted over long distances at high voltage because

Accepted Answer

Transmitting electric power at high voltage reduces the current in the transmission lines, which in turn reduces the power lost as heat due to the resistance of the wires (P=I^2R). This makes the transmission more efficient over long distances.

Question 11

A horizontal rod (oriented in the east-west direction) is moved northward at constant velocity through a magnetic field that points straight down. Make a statement concerning the potential induced across the rod.

Accepted Answer

According to the right-hand rule and Faraday's law of electromagnetic induction, the west end of the rod will be at a higher potential than the east end when the rod moves northward through a downward magnetic field.

Question 12

FIGURE 29-4 -Fig. 29-4 shows the time evolution of a uniform magnetic field. Four particular instants labeled t_A to t_D are also identified on the graph. The field passes through a circular coil whose normal is parallel to the direction of the field. At what time does the current induced in the coil have the largest value?

Accepted Answer

The answer of FIGURE 29-4 
-Fig. 29-4 shows the time...

Question 13

FIGURE 29-8 
-A metallic frame moving along the positive direction enters a region of space with a uniform magnetic field pointing in the positive z direction as shown in Fig. 29-8. In what direction should a force be applied to the frame to keep it moving at a constant speed while it is entering the field?

Accepted Answer

The answer of FIGURE 29-8 
-A metallic frame moving along...

Question 14

A coil is rotating at constant speed within a uniform magnetic field. What can be said about the magnitude of the emf induced in the coil?

Accepted Answer

The answer of A coil is rotating at constant speed...

Question 15

FIGURE 29-10 
-A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be zero?

Accepted Answer

The induced emf is zero when the plane of the loop is parallel to the magnetic field lines, meaning the axis of rotation must be vertical.

Question 16

An electric generator transforms

Accepted Answer

An electric generator converts mechanical energy into electrical energy by using electromagnetic induction.

Question 17

FIGURE 29-11 -A 200-loop coil of cross sectional area 8.5 cm² lies in the plane of the paper. Directed out of the plane of the paper is a magnetic field of 0.06 T. The field out of the paper decreases to 0.02 T in 12 milliseconds. (a) What is the magnitude of the change in magnetic flux enclosed by the coil? (b) What is the average voltage induced in the coil as the flux is changing? (c) If the coil has a resistance of 4.0 ohms, what is the magnitude of the current in the coil?

Accepted Answer

The answer of FIGURE 29-11 
-A 200-loop coil of cross...

Question 18

If the number of turns on the secondary coil of a transformer are less than those on the primary, the result is a

Accepted Answer

A transformer with fewer turns on the secondary coil compared to the primary coil is a step-down transformer, as it reduces the voltage.

Question 19

In a transformer, the power input

Accepted Answer

In an ideal transformer, the power input is equal to the power output.

Question 20

Electric fields produced by changing magnetic fields

Accepted Answer

Electric fields produced by changing magnetic fields are nonconservative because they are associated with induced electromotive forces (EMF) and do not have a potential function. This is described by Faraday's law of electromagnetic induction.

Quiz 29: Electromagnetic Induction and Faradays Law

FIGURE 29-10 -A rectangular coil with N turns, length L, and width w, as shown in Fig. 29-10, is rotating in a magnetic field B with an angular frequency ω. If the area of the coil is A, what is the induced emf in the coil?