Chapter 21, Exam #2/3

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

When a magnetic field is tilted

When the size of the coil decreases

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

zero

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 L

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

first loop-zero

second loop- clockwise

If there is induced current in Question 18 (see Fig. 21-51), wouldn't that cost energy? Where would that energy come from in case?

less kinetic energy

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 emf will be produced but no current

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.

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 changed

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

Whatever rotates the generators axel.

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

Rotating the magnetic field so that is more closely parallel to the generators rotation axis.

Which of the following can a transformer accomplish?

Changing both current and voltage

A laptop computer's charger unit converts 120 V from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is a diode or rectifier (discussed in Chapter 29) that changes ac to dc plus a

transformer

Which of the following statements about transformers is false?

Transformers work using ac current or dc current

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 and 0 A

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

a rotating coil that is immersed in a magnetic field

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

Swipe the card more quickly so the induced emf is higher

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

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