Physics Misconception Questions Exam 2

A loop rests in the plane of a page of textbook while a magnetic field is directed into the page. A clockwise current is induced

- when the magnetic field is tilted so it is no longer perpendicular to the page - when the size of the loop decreases

CHAPTER 21

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Two identical 10-V batteries and two identical 10-Ω resistors are placed in series as shown in Fig. 19-42. If a 10-Ω lightbulb is connected with one end connected between the batteries and other end between the resistors, how much current will flow through the lightbulb?

0 A

A 10-V, 1.0-A dc current is run through a step-up transformer that has 10 turns on the input side and 20 turns on the output side. What is the output?

0 V, 0 A

A 10,000-Ω resistor is placed in series with a 100-Ω resistor. The current in the 10,000-Ω resistor is 10 A. If the resistors are swapped, how much current flows through the 100-Ω resistor?

10 A

CHAPTER 19

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CHAPTER 20

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Which of the following can a transformer accomplish?

Changing both current and voltage

The junction rule describes the conservation of which quantity? Note that this rule applies only to circuits that are in a steady state.

charge

When the switch shown in Fig. 19-45 is closed, what will happen to the voltage across resistor R1? It will

increase

A wire loop moves at constant velocity without rotation through a constant magnetic field. The induced current in the loop will be

zero

The capacitor in the circuit shown in Fig. 19-47 is charged to an initial value Q. When the switch is closed, it discharges through the resistor. It takes 2.0 seconds for the charge to drop to 1/2 Q. How long does it take to drop to 1/4 Q?

4.0 seconds

In which circuits shown in Fig. 19-40 are resistors connected in series?

A & C

Indicate which of the following will produce a magnetic field: a) A magnet b) earth c) electric charge at rest d) moving electric charge e) electric current f) voltage of a battery not connected to anything g) ordinary piece of iron h) a piece of any metal

A, B, D, E

Figure 19-44 shows three identical bulbs in a circuit. What happens to the brightness of bulb A if you replace bulb B with a short circuit?

Bulb A goes out

Two wire loops are moving in the vicinity of a very long straight wire carrying a steady current. Find the direction of the induced current in each loop.

For C: zero For D: clockwise

A long straight wire carries a current, I, as shown in Fig. 21-55. A small loop of wire rests in the plane of the page. Which of the following will not induce a current in the loop?

Moving the loop in a direction parallel to the wire

Which resistors in Fig. 19-41 are connected in parallel?

R1 and R3

Which resistor shown in Fig. 19-43 has the greatest current going through it? Assume that all the resistors are equal.

R5

Which of the following will not increase a generator's voltage output?

Rotating the magnetic field so that it is more closely parallel to the generator's rotation axis

When you swipe a credit card, the machine sometimes fails to read the card. What can you do differently?

Swipe the card quicker so that the induced EMF is higher

For the circuit shown in Fig. 19-46, what happens when the switch S is closed?

The capacitor eventually charges up to the full battery emf at a rate determined by R and C.

Which of the following is true about all series ac circuits?

The current at any point in the circuit is always the same as the current at any other point in the circuit

How does the current through R1 compare with the current through R2 a very long time after the switch has been closed?

The current through R1 is equal to the current through R2

How does the current through R1 compare with the current through R2 immediately after the switch is opened (after being closed a very long time)?

The current through R1 is less than the current through R2

Why is an appliance cord with a three-prong plug safer than one with two prongs?

The third prong grounds the case, so the case cannot reach a high voltage.

Two parallel wires are vertical. The one on the left carries a 10 A current upward. The other carries 5 A current downward. Compare the magnitude of the force that each wire exerts on the other.

The two wires exert the same force on each other

If there is an induced current, wouldn't that cost energy? (see Fig. 21-51) Where would that energy come from in case A?

There is less kinetic energy

Wire carries I away from you; which way do the magnetic field lines produced by this wire point?

They make circles around the wire

Which of the following statements about transformers is false?

Transformers work using ac current or dc current

When a generator is used to produce electric, the resulting electric energy originates from which source?

Whatever rotates the generator's axel

The alternating electric current at a wall outlet is most commonly produced by

a rotating coil that is immersed in a magnetic field

Which of the following statements about the force on a charged particle due to a magnetic field are NOT valid?

all statements are valid

A nonconducting plastic hoop is held in a magnetic field that points out of the page (Fig. 21-54). As the strength of the field increases,

an induced EMF will be produced but no current

A nonconducting plastic hoop is held in a magnetic field that points out of the figure (Figure 1). As the strength of the field increases,

an induced emf will be produced but no current.

A square loop moves to the right from an area where B=0, completely through a region containing a uniform magnetic field directed into the page, and then out to B=0 after point L. A current is induced in the loop...

as it passes line J or line L

A square loop moves to the right from an area where B→=0, completely through a region containing a uniform magnetic field directed into the figure (Figure 1), and then out to B=0 after point L. A current is induced in the loop

as it passes line J or line L

In which direction is the magnetic field at point B?

b) left

As a proton moves through space, it creates?

both an electric field and a magnetic field

A current in a wire points into the page; which direction is the magnetic field at point A?

c) down

When the switch shown in Fig. 19-45 is closed, what will happen to the voltage across resistor R4? It will

decrease

As a capacitor is being charged in an RC circuit, the current flowing through the resistor is

decreasing

Which of the following is false? The B of a current carrying wire...

exists only if the current in the wire is changing

When capacitors are connected in series, the effective capacitance is _______ the smallest capacitance; when capacitors are connected in parallel, the effective capacitance is _________ the largest capacitance.

less than; greater than

Which statements about the force on a charged particle placed in a magnetic field are true?

magnetic force exerted only if particle is moving

A resistor and a capacitor are used in series to control the timing in the circuit of a heart pacemaker. To design a pacemaker that can double the heart rate when the patient is exercising, which statement below is true? The capacitor

needs to discharge faster, so the resistance should be decreased.

For a charged particle, a constant magnetic field can be used to change...

only the direction of the particle's velocity

Two separate but nearby coils are mounted along the same axis. A power supply controls the flow of current in the first coil, and thus the magnetic field it produces. The second coil is connected only to an ammeter. The ammeter will indicate that a current is flowing in the second coil...

only when the current in the first coil changes

Two separate but nearby coils are mounted along the same axis. A power supply controls the flow of current in the first coil, and thus the magnetic field it produces. The second coil is connected only to an ammeter. The ammeter will indicate that a current is flowing in the second coil

only when the current in the first coil changes.

A proton enters a uniform magnetic field that is perpendicular to the protons velocity; what happens to KE of proton?

stays the same

When a charged particle moves parallel to the direction of a magnetic field, the particle travels a?

straight line

How does the current through R1 compare with the current through R2 immediately after the switch is first closed?

the current through R1 is greater than the current through R2

If ammeters and voltmeters are not to significantly alter the quantities they are measuring,

the resistance of an ammeter should be much lower, and the resistance of a voltmeter should be much higher, than those of the circuit being measured.

A laptop computer's charger unit converts 120V from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is diode or rectifier that changes ac to dc plus a...

transformer

A coil rests in the plane of the page while a magnetic field is directed into the page. A clockwise current is induced

when the size of the coil decreases when the magnetic field is tilted so it's no longer perpendicular to the page