What is a voltage transformer?

B. A transformer is a device that transforms voltages from one value to another.

A. A transformer is a device that transforms current to voltage.

C. A transformer is a device that transforms resistance of wire to voltage.

Why is electric power transmitted at high voltage?

B. To reduce energy loss during transmission

A. To increase the current for the transmission

C. To increase resistance during transmission

D. To reduce resistance during transmission

To obtain power from the current in the wire of your vacuum cleaner, you place a loop of wire near it to obtain an induced emf. How do you place and orient the loop?

A. A loop of wire should be placed nearest to the vacuum cleaner wire to maximize the magnetic flux through the loop.

B. A loop of wire should be placed farthest to the vacuum cleaner wire to maximize the magnetic flux through the loop.

C. A loop of wire should be placed perpendicular to the vacuum cleaner wire to maximize the magnetic flux through the loop.

D. A loop of wire should be placed at angle greater than 90° to the vacuum cleaner wire to maximize the magnetic flux through the loop.

A magneto is a device that creates a spark across a gap by creating a large voltage across the gap. To do this, the device spins a magnet very quickly in front of a wire coil, with the ends of the wires forming the gap. Explain how this creates a sufficiently large voltage to produce a spark.

B. The magnetic field in the coil changes rapidly due to spinning of magnet which creates an emf in the coil that is proportional to the rate of change of the magnetic flux.

A. The electric field in the coil increases rapidly due to spinning of magnet which creates an emf in the coil that is proportional to the rate of change of the magnetic flux.

If you drop a copper tube over a bar magnet with its north pole up, is a current induced in the copper tube? If so, in what direction? Consider when the copper tube is approaching the bar magnet.

A. Yes, the induced current will be produced in the clockwise direction when viewed from above.

B. No, the induced current will not be produced.

How can you maximize the peak emf from a generator?

D. The peak emf from a generator can be maximized by maximizing number of turns, maximizing area of the wired loop or maximizing frequency.

A. The peak emf from a generator can be maximized only by maximizing number of turns.

B. The peak emf from a generator can be maximized only by maximizing area of the wired loop.

C. The peak emf from a generator can be maximized only by maximizing frequency.

Explain why power is transmitted over long distances at high voltages.

D. P_transmitted = I_transmitted V_transmitted, so to minimize current, the voltage must be maximized

A. P_lost = I_transmitted V_transmitted, so to maximize current, the voltage must be maximized

B. P_transmitted = I_transmitted V_transmitted, so to maximize current, the voltage must be maximized

C. P_lost = I_transmitted V_transmitted, so to minimize current, the voltage must be maximized

For a magnet, a domain refers to ______.

C. the region within the magnet in which the magnetic poles of individual atoms are aligned

A. the region between the poles of the magnet

B. the space around the magnet that is affected by the magnetic field

D. the region from which the magnetic material is mined

In the region just outside the south pole of a magnet, the magnetic field lines ______.

A. point away from the south pole

C. are less concentrated than at the north pole

Can magnetic field lines cross each other? Explain why or why not.

B. No, magnetic field lines cannot cross each other because that point of intersection indicates two possible directions of magnetic field, which is not possible.

A. Yes, magnetic field lines can cross each other because that point of intersection indicates two possible directions of magnetic field, which is possible.

What is the relationship between the number of coils in a solenoid and the emf induced in it by a change in the magnetic flux through the solenoid?

B. The induced emf is directly proportional to the number of coils in a solenoid.

A. The induced emf is inversely proportional to the number of coils in a solenoid.

C. The induced emf is inversely proportional to the square of the number of coils in a solenoid.

D. The induced emf is proportional to square of the number of coils in a solenoid.

An electrical generator ________.

C. converts other sources of power into electrical power

A. is a generator powered by electricity

D. uses magnetism to create electrons

A step-up transformer increases the

D. voltage from the electrical power plant for transmission along power lines

A. voltage from power lines for use in homes

B. current from the power lines for use in homes

C. current from the electrical generator for transmission along power lines

Why are the coils of a transformer wrapped around a loop of ferrous material?

A. The magnetic field from the source coil is trapped and also increased in strength.

B. The magnetic field from the source coil is dispersed and also increased in strength.

C. The magnetic field from the source coil is trapped and also decreased in strength.

D. Magnetic field from the source coil is dispersed and also decreased in strength.

Given a bar magnet, a needle, a cork, and a bowl full of water, describe how to make a compass.

C. Magnetize the needle by holding its axis parallel to the axis of a bar magnet and pierce the cork along its longitudinal axis by the needle and place the needle-cork combination in the water. The needle now orients itself along the magnetic field lines of Earth.

A. Magnetize the needle by holding it perpendicular to a bar magnet’s north pole and pierce the cork along its longitudinal axis by the needle and place the needle-cork combination in the water. The needle now orients itself along the magnetic field lines of Earth.

B. Magnetize the needle by holding it perpendicular to a bar magnet’s north pole and pierce the cork along its longitudinal axis by the needle and place the needle-cork combination in the water. The needle now orients itself perpendicular to the magnetic field lines of Earth.

D. Magnetize the needle by holding its axis parallel to the axis of a bar magnet and pierce the cork along its longitudinal axis by the needle and place the needle-cork combination in the water. The needle now orients itself perpendicular to the magnetic field lines of Earth.

Give two differences between electric field lines and magnetic field lines.

A. Electric field lines begin and end on opposite charges and the electric force on a charge is in the direction of field, while magnetic fields form a loop and the magnetic force on a charge is perpendicular to the field.

B. Electric field lines form a loop and the electric force on a charge is in the direction of field, while magnetic fields begin and end on opposite charge and the magnetic force on a charge is perpendicular to the field.

C. Electric field lines begin and end on opposite charges and the electric force on a charge is in the perpendicular direction of field, while magnetic fields form a loop and the magnetic force on a charge is in the direction of the field.

D. Electric field lines form a loop and the electric force on a charge is in the perpendicular direction of field, while magnetic fields begin and end on opposite charge and the magnetic force on a charge is in the direction of the field.

You magnetize a needle by aligning it along the axis of a bar magnet and just outside the north pole of the magnet. Will the point of the needle that was closest to the bar magnet then be attracted to or repelled from the south pole of another magnet?

A. The needle will magnetize and the point of needle kept closer to the north pole will act as a south pole. Hence, it will repel the south pole of other magnet.

B. The needle will magnetize and the point of needle kept closer to the north pole will act as a south pole. Hence, it will attract the south pole of other magnet.

C. The needle will magnetize and the point of a needle kept closer to the north pole will act as a north pole. Hence, it will repel the south pole of the other magnet.

D. The needle will magnetize and the point of needle kept closer to the north pole will act as a north pole. Hence, it will attract the south pole of other magnet.

A uniform magnetic field is perpendicular to the plane of a wire loop. If the loop accelerates in the direction of the field, will a current be induced in the loop? Explain why or why not.

A. No, because magnetic flux through the loop remains constant.

B. No, because magnetic flux through the loop changes continuously.

C. Yes, because magnetic flux through the loop remains constant.

D. Yes, because magnetic flux through the loop changes continuously.

Yes or no—If a bar magnet moves through a wire loop as shown in the figure below, is a current induced in the loop? Explain why or why not.

A. No, because the net magnetic field passing through the loop is zero.

B. No, because the net magnetic field passing through the loop is nonzero.

C. Yes, because the net magnetic field passing through the loop is zero.

D. Yes, because the net magnetic field line passing through the loop is nonzero.

A laminated-coil transformer has a wire coiled 12 times around one of its sides. How many coils should you wrap around the opposite side to get a voltage output that is one half of the input voltage? Explain.

A. six output coils because the ratio of output to input voltage is the same as the ratio of number of output coils to input coils

B. 12 output coils because the ratio of output to input voltage is the same as the ratio of number of output coils to input coils

C. 24 output coils because the ratio of output to input voltage is half the ratio of the number of output coils to input coils

D. 36 output coils because the ratio of output to input voltage is three times the ratio of the number of output coils to input coils

How is the output emf of a generator affected if you double the frequency of rotation of its coil?

A. The output emf will be doubled.

B. The output emf will be halved.

C. The output emf will be quadrupled.

D. The output emf will be tripled.

In a hydroelectric dam, what is used to power the electrical generators that provide electric power? Explain.

D. Gravitational potential energy of stored water is used to produce emf with the help of a turbine.

A. The electric potential energy of stored water is used to produce emf with the help of a turbine.

B. The electric potential energy of stored water is used to produce resistance with the help of a turbine.

C. Gravitational potential energy of stored water is used to produce resistance with the help of a turbine.

Summarize the properties of magnets.

B. A magnet can attract metals like iron, nickel, etc., but cannot attract nonmetals like piece of plastic or wood, etc. If free to rotate, an elongated magnet will orient itself so that its north pole will face the magnetic north pole of Earth.

A. A magnet can attract metals like iron, nickel, etc., but cannot attract nonmetals like piece of plastic or wood, etc. If free to rotate, an elongated magnet will orient itself so that its north pole will face the magnetic south pole of Earth.

C. A magnet can attract metals like iron, nickel, etc., and nonmetals like piece of plastic or wood, etc. If free to rotate, an elongated magnet will orient itself so that its north pole will face the magnetic south pole of Earth.

D. A magnet can attract metals like iron, nickel, etc., and nonmetals like piece of plastic or wood, etc. If free to rotate, an elongated magnet will orient itself so that its north pole will face the magnetic north pole of Earth.

The magnetic field shown in the figure below is formed by current flowing in two rings that intersect the page at the dots. Current flows into the page at the dots with crosses (right side) and out of the page at the dots with points (left side). Where is the field strength the greatest and in what direction do the magnetic field lines point?

B. The magnetic field strength is greatest where the magnetic field lines are most dense; magnetic field lines points up the page.

A. The magnetic field strength is greatest where the magnetic field lines are less dense; magnetic field lines points up the page.

C. The magnetic field strength is greatest where the magnetic field lines are most dense; magnetic field lines points down the page.

D. The magnetic field strength is greatest where the magnetic field lines are less dense; magnetic field lines points down the page.

The forces shown below are exerted on an electron as it moves through the magnetic field. In each case, what direction does the electron move?"]

B. (a) left to right, (b) into the page, (c) downwards

A. (a) left to right, (b) out of the page, (c) upwards

C. (a) right to left, (b) out of the page, (c) upwards

D. (a) right to left, (b) into the page, (c) downwards

When you insert a copper ring between the poles of two bar magnets as shown in the figure below, do the magnets exert an attractive or repulsive force on the ring? Explain your reasoning.

C. Magnets exert a repulsive force, because magnetic field due to induced current is repulsed by the magnetic field of the magnets.

A. Magnets exert an attractive force, because magnetic field due to induced current is repulsed by the magnetic field of the magnets.

B. Magnets exert an attractive force, because magnetic field due to induced current is attracted by the magnetic field of the magnets.

D. Magnets exert a repulsive force, because magnetic field due to induced current is attracted by the magnetic field of the magnets.

The figure below shows a uniform magnetic field passing through a closed wire circuit. The wire circuit rotates at an angular frequency of about the axis shown by the dotted line in the figure. What is an expression for the magnetic flux through the circuit as a function of time?

B. expression for the magnetic flux through the circuit Φ(t) = sqrt 2 BAcos⁡ωt

A. expression for the magnetic flux through the circuit Φ(t) = BAcos⁡ωt

C. expression for the magnetic flux through the circuit Φ(t) = sqrt 3 BAcos⁡ωt

D. expression for the magnetic flux through the circuit Φ(t) = 2BA cos ωt

Copy of Physics - Chapter 20 - Magnetism

Authored by Moses Ntam

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Copy of Physics - Chapter 20 - Magnetism

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MULTIPLE CHOICE QUESTION

30 sec • 1 pt

If you place a small needle between the north poles of two bar magnets, will the needle become magnetized?

A. Yes, the magnetic fields from the two north poles will point in the same directions.

B. Yes, the magnetic fields from the two north poles will point in opposite directions.

C. No, the magnetic fields from the two north poles will point in opposite directions.

D. No, the magnetic fields from the two north poles will point in the same directions.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

If you place a compass at the three points in the figure below, at which point will the needle experience the greatest torque? Why?

A. The density of the magnetic field is minimized at B, so the magnetic compass needle will experience the greatest torque at B.

B. The density of the magnetic field is minimized at C, so the magnetic compass needle will experience the greatest torque at C.

C. The density of the magnetic field is maximized at B, so the magnetic compass needle will experience the greatest torque at B.

D. The density of the magnetic field is maximized at A, so the magnetic compass needle will experience the greatest torque at A.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

In which direction do the magnetic field lines point near the south pole of a magnet?

A. Outside the magnet the direction of magnetic field lines is towards the south pole of the magnet.

B. Outside the magnet the direction of magnetic field lines is away from the south pole of the magnet.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Yes or no—Is an emf induced in the coil shown below when it is stretched? If so, state why and give the direction of the induced current.

A. No, because induced current does not depend upon the area of the coil.

B. Yes, because area of the coil increases; the direction of the induced current is counterclockwise.

C. Yes, because area of the coil increases; the direction of the induced current is clockwise.

D. Yes, because the area of the coil does not change; the direction of the induced current is clockwise.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is Lenz’s law?

A. If induced current flows, its direction is such that it adds to the changes which induced it.

B. If induced current flows, its direction is such that it opposes the changes which induced it.

C. If induced current flows, its direction is always clockwise to the changes which induced it.

D. If induced current flows, its direction is always counterclockwise to the changes which induced it.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Explain how magnetic flux can be zero when the magnetic field is not zero.

A. If angle between magnetic field and area vector is 0°, then its sine is also zero, which means that there is zero flux.

B. If angle between magnetic field and area vector is 45°, then its sine is also zero, which means that there is zero flux.

C. If angle between magnetic field and area vector is 60°, then its cosine is also zero, which means that there is zero flux.

D. If the angle between magnetic field and area vector is 90°, then its cosine is also zero, which means that there is zero flux.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Consider the angle between the area vector and the magnetic field in an electric motor. At what angles is the torque on the wire loop the greatest?

A. 0° and 180°

B. 45° and 135°

C. 90° and 270°

D. 225° and 315°

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Copy of Physics - Chapter 20 - Magnetism

If you place a small needle between the north poles of two bar magnets, will the needle become magnetized?

If you place a compass at the three points in the figure below, at which point will the needle experience the greatest torque? Why?

In which direction do the magnetic field lines point near the south pole of a magnet?

Yes or no—Is an emf induced in the coil shown below when it is stretched? If so, state why and give the direction of the induced current.

What is Lenz’s law?

Explain how magnetic flux can be zero when the magnetic field is not zero.

Consider the angle between the area vector and the magnetic field in an electric motor. At what angles is the torque on the wire loop the greatest?

What is a voltage transformer?

Why is electric power transmitted at high voltage?

True or false—It is not recommended to place credit cards with magnetic strips near permanent magnets.

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