physics exam 2 multiple choice (ch 21)

Four views of a horseshoe magnet and a current-carrying wire are shown in the drawing. The wire is perpendicular to the screen, and the current is directed out of the screen toward you. In which one or more of these situations does the magnetic force on the current point due north? 2 1 3 and 4 1 and 2 3

1

The drawing shows four situations in which a positively charged particle is moving with a velocity v through a magnetic field B. In each case, the magnetic field is directed out of the screen toward you, and the velocity is directed to the right. In only one of these drawings is the magnetic force F physically reasonable. Which one is it? 3 2 4 1

1

Three particles are moving perpendicular to a uniform magnetic field and travel on circular paths (see the drawing). They have the same mass and speed. List the particles in order of their charge magnitude, largest to smallest. 1, 2, 3 3, 2, 1 1, 3, 2 3, 1, 2 2, 3, 1

1, 2, 3

The drawing shows four situations in which two very long wires are carrying the same current, although the direction of the currents may be different. The point P in the drawings is equidistant from each wire. Which one (or more) of these situations gives rise to a zero net magnetic field at P? 3 and 4 2 and 3 2 and 4 Only 1 Only 2

2 and 4

The figure shows three identical charged particles moving with the same speed but at different directions in a uniform magnetic field. Rank the charges in order of the magnetic force each one experiences, starting with the largest. 1, 2, 3 3, 1, 2 3, 2, 1 2, 1, 3

2, 1, 3

A changing magnetic field induces an emf of 5.0 V in a single-loop of wire. Suppose the single loop were replaced by one continuous wire wrapped to form a coil of five loops, each with the same size and shape as the original loop, and placed in the same changing magnetic field and with the same orientation as the single loop. What would be the magnitude of the induced emf in the coil?

25 V

Suppose that when you move the north pole of a bar magnetic toward a coil it induces a positive current in the coil. The strength of the field produced by an electromagnetic can be controlled electronically. Suppose you place a coil near the north pole of an electromagnet and increase the field while keeping everything stationary. Which one of the following will happen?

A positive current will be induced in the coil.

Which of the following is/are true? A mass spectrometer has many uses in both physics and chemistry. A mass spectrometer can be used to identify charged particles with different masses. A mass spectrometer takes advantage of the fact that charged particles are deflected into circular trajectories within a magnetic field. All of the above are true.

All of the above are true.

A circular coil of N turns rotates at some frequency in a constant magnetic field and produces an emf. Which of the following will double the emf?

Any one of the above.

Three long, straight wires are carrying currents that have the same magnitude. In C the current is opposite to that in A and B. The wires are equally spaced. Each wire experiences a net force due to the other two wires. Which wire experiences a net force that has the greatest magnitude? B A C All three wires experience a net force that has the same magnitude.

B

At a location near the equator, the earth's magnetic field is horizontal and points north. An electron is moving vertically upward from the ground. What is the direction of the magnetic force that acts on the electron? South East West North The magnetic force is zero

East

Suppose that the emf from a rod moving in a magnetic field was used to supply the current to illuminate a light bulb in a circuit, and the force needed to keep the rod moving is F. What happens to the force needed drive the motion of the rod if the light bulb is removed?

No force is needed: there is no longer a magnetic force to oppose the motion.

Suppose that a magnet and a coil were dropped together from the same height at the same time. Would there be an induced current in the coil?

No, because, as they fall together, they are not moving relative to each other.

Which of the following does not produce a change in magnetic flux through a square loop of wire?

The loop falls through a uniform magnetic field without rotating.

A current carrying wire is experiencing a magnetic force in a magnetic field. What happens to the direction of the magnetic force on the wire, if the current in the wire is reversed? The magnitude of the force remains unchanged, but it is oriented perpendicular to the direction of the original force. The magnitude of the forces decreases, but it remains in the same direction. Nothing. The magnitude and direction of the force remain unchanged. The magnitude of the force remains unchanged, but it reverses direction.

The magnitude of the force remains unchanged, but it reverses direction.

A proton is released from rest at a location in space where the magnetic field points upward toward the top of the page. Which of the following is true? The proton experiences a magnetic force to the right. The proton experiences no magnetic force and remains at rest. The proton experiences a magnetic force upward. The proton experiences a magnetic force downward.

The proton experiences no magnetic force and remains at rest.

Suppose the current through a light bulb in a circuit is provided by the motional emf of a rod moving in a magnetic field. If you wanted to keep the intensity of the light emitted by the bulb constant when the strength of the magnetic field is doubled, how should the speed of the rod be changed?

The speed of the rod should be halved.

A compass is placed in a magnetic field, and the compass needle is oriented as shown in the figure (up). What is the direction of the magnetic field at the location of the compass? Up Down Left Right

Up

A positive charge is moving with velocity v through a region of space where a uniform magnetic field exists everywhere into the screen, as the figure shows. What is the direction of the magnetic force on the charge just as it enters the field? Downward Left Right Out of the screen Into the screen Upward

Upward

A square current-carrying loop is placed in a uniform magnetic field B with the plane of the loop parallel to the magnetic field (see the drawing). The dashed line is the axis of rotation. The magnetic field exerts _____________ neither a net force nor a net torque on the loop. a net force and a net torque on the loop. a net force, but not a net torque, on the loop. a net torque, but not a net force, on the loop.

a net torque, but not a net force, on the loop.

The drawing shows the circular paths of an electron and a proton. These particles have the same charge magnitudes, but the proton is more massive. They travel at the same speed in a uniform magnetic field B, which is directed into the screen everywhere. Which particle follows the larger circle, and does it travel clockwise or counterclockwise? b. c. d. a.

d

The figure shows a mass spectrometer that is calibrated to detect a particular charged particle whose mass is m1 (path 1)? If the charged particles traveling along path 2 are an isotope of those traveling along path 1, how does the mass of particle 2 compare to the mass of particle 1?

m1 < m2