Physics Test 3 Misconceptual Questions

For a charged particle, a constant magnetic field can be used to change (a) only the direction of the particle's velocity. (b) only the magnitude of the particle's velocity. (c) both the magnitude and direction of the particle's velocity. (d) None of the above.

(A): Only the direction of the particle's velocity

Which of the following statements about the force on a charged particle due to a magnetic field are not valid? (a) It depends on the particle's charge. (b) It depends on the particle's velocity. (c) It depends on the strength of the external magnetic field. (d) It acts at right angles to the direction of the particle's motion. (e) None of the above; all of these statements are valid.

(E): None of the above, all of the statements are valid

When a charged particle moves parallel to the direction of a magnetic field, the particle travels in a (a) straight line. (c) helical path. (b) circular path. (d) hysteresis loop.

(a) A straight Line

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

(a), (b), (d), (e), (c)- does not due to no movement of charge. Only moving charge-creating a flux-can product a magnetic field but the charge at rest will not. (f)-cannot due to an open circuit

Which of the following statements is false? The magnetic field of a current-carrying wire (a) is directed circularly around the wire. (b) decreases inversely with the distance from the wire. (c) exists only if the current in the wire is changing. (d) depends on the magnitude of the current.

(c) exists only if the current in the wire is changing

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. (a) The wire on the left carries twice as much current, so it exerts twice the force on the right wire as the right one exerts on the left one. (b) The wire on the left exerts a smaller force. It creates a magnetic field twice that due to the wire on the right; and therefore has less energy to cause a force on the wire on the right. (c) The two wires exert the same force on each other. (d) Not enough information; we need the length of the wire.

(c): the two wires exert the same force on each other

A wire carries a current directly away from you. Which way do the magnetic field lines produced by this wire point? (a) They point parallel to the wire in the direction of the current. (b) They point parallel to the wire opposite the direction of the current. (c) They point toward the wire. (d) They point away from the wire. (e) They make circles around the wire.

(e) they make circles around the wires

Can you set a resting electron into motion with a magnetic field? With an electric field? Explain.

-An electron at rest will not experience any magnetic force because F=BqVsinθ. As V = 0 F=0 -As an electron at rest can be set into motion by an electric field, as the electron force is independent of the speed of the electron F=qE

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 D: (loop with v pointing to the right)

-Clockwise for D

A 10V, 1.0A 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?

0V, 0A

Which statements about the force on a charged particle placed in a magnetic field are true? (a) A magnetic force is exerted only if the particle is moving. (b) The force is a maximum if the particle is moving in the direction of the field. (c) The force causes the particle to gain kinetic energy. (d) The direction of the force is along the magnetic field. (e) A magnetic field always exerts a force on a charged particle.

A magnetic field is only exerted is a particle is moving

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

A rotating coil that is immersed in a magnetic field

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...

A transformer

A non-conducting plastic hoop is held in a magnetic field that points out of the page (Fig. 21-54). As the strength of the field increases.. (A larger loop with four smaller loops with dots in them)

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

As a proton moves through space, it creates (a) an electric field only. (b) a magnetic field only. (c) both an electric field and magnetic field. (d) nothing; the electric field and magnetic fields cancel each other out.

Both an electric and a magnetic field

Which of the following can a transformer accomplish?

Changing both current and voltage

In what direction are the magnetic field lines surrounding a straight wire carrying a current that is moving directly away from you? Explain.

Clockwise circles centered on the wire via the right hand rule

A proton enters a uniform magnetic field that is perpendicular to the proton's velocity (Fig. 20-51). What happens to the kinetic energy of the proton? (a) It increases. (b) It decreases. (c) It stays the same. (d) It depends on the velocity direction. (e) It depends on the B field direction. C. It stays the same

It stays the same

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

Less kinetic energy is present

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? (Loop under a line of current pointing to the right)

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 changes

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 generators 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

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

Three particles, a, b, and c, enter a magnetic field and follow paths as shown in Fig. 20-48. What can you say about the charge on each particle? Explain.

The magnetic field points into the plane of the paper (a): upward and positive (b): neutral and unchanged (c): downward and negative

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 current, the resulting electric energy originates from which source?

Whatever rotates generator's axle

.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 or when the magnetic field is tilted so it no longer is perpendicular to the page

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

Zero

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: (loop with v pointing up in parallel with I)

Zero for C