Physics Chapter 21

The drawing shows a conducting wire wound into a helical shape. The helix acts like a spring and expands back toward its original shape after the coils are squeezed together and released. The bottom end of the wire just barely touches the mercury (a good electrical conductor) in the cup. After the switch is closed, current in the circuit causes the light bulb to glow. Does the bulb (a) repeatedly turn on and off like a turn signal on a car, (b) glow continually, or (c) glow briefly and then go out? (a) (b) (c)

(a)

For each electromagnet at the left in the drawing, will it be attracted to or repelled from the electromagnet immediately to its right? (a) repelled (b) repelled (a) attracted (b) repelled (a) repelled (b) attracted (a) attracted (b) attracted

(a) attracted (b) repelled

Refer to the figure below. (a) What happens to the direction of the magnetic force if the current is reversed? (b) What happens to the direction of the force if both the current and the magnetic poles are reversed? (a) Its direction reverses. (b) Its direction reverses. (a) Its direction reverses. (b) Its direction does not change. (a) Its direction does not change. (b) Its direction does not change. (a) Its direction does not change. (b) Its direction reverses.

(a) its direction reverses. (b) its direction does not change.

For each electromagnet at the left in the drawing, will it be attracted to or repelled from the permanent magnet immediately to its right? (a) repelled (b) repelled (a) attracted (b) repelled (a) attracted (b) attracted (a) repelled (b) attracted

(a) repelled (b) repelled

In the figure below, assume that the current I1 is larger than the current I2. In parts a and b, decide whether there are places at which the total magnetic field is zero. State whether these places are located to the left of both wires, between the wires, or to the right of both wires. (a) to the left of both wires (b) between the wires (a) between the wires (b) between the wires (a) to the right of both wires (b) between the wires

(a) to the right of both wires (b) between the wires

The drawing shows a particle carrying a positive charge +q at the coordinate origin, as well as a target located in the third quadrant. A uniform magnetic field is directed perpendicularly into the plane of the paper. The charge can be projected in the plane of the paper only, along the positive or negative x or y axis. There are four possible directions (+x, -x, +y, -y) for the initial velocity of the particle. The particle can be made to hit the target for only two of the four directions. Which two directions are they? -x, +y -y, +x +y, -y +x, -x

-x, +y

Each of the four drawings shows the same three concentric loops of wire. The currents in the loops have the same magnitude I and have the directions shown. Rank the magnitude of the net magnetic field produced at the center of each of the four drawings, largest to smallest. D, C, B, A A, D, C, B B, C, D, A A, B, C, D

A, D, C, B

The drawing shows a top view of four interconnected chambers. A negative charge is fired into chamber 1. By turning on separate magnetic fields in each chamber, the charge can be made to exit from chamber 4, as shown. How should the magnetic field in each chamber be directed: out of the page or into the page? A. Chamber 1: out of; Chamber 2: into; Chamber 3: out of; Chamber 4: into B. Chamber 1: into; Chamber 2: out of; Chamber 3: out of; Chamber 4: into C. Chamber 1: out of; Chamber 2: into; Chamber 3: into; Chamber 4: out of D. Chamber 1: into; Chamber 2: out of; Chamber 3: into; Chamber 4: out of

B

The same current-carrying wire is placed in the same magnetic field Upper B Overscript right-arrow EndScripts in four different orientations (see the drawing). Rank the orientations according to the magnitude of the magnetic force exerted on the wire, largest to smallest. A, B, C, D A and B (a tie), C, D B and D (a tie), A, C A and C (a tie), B, D

B and D (a tie), A, C

Suppose that you have two bars. Bar 1 is a permanent magnet and bar 2 is not a magnet, but is made from a ferromagnetic material like iron. A third bar (bar 3), which is known to be a permanent magnet, is brought close to one end of bar 1 and then to one end of bar 2. Which one of the following statements is true? Bars 1 and 3 will always be attracted to each other, while bars 2 and 3 will either be attracted to or repelled from each other. Bars 1 and 3 will always be repelled from each other, while bars 2 and 3 will either be attracted to or repelled from each other. Bars 1 and 3 will either be attracted to or repelled from each other, while bars 2 and 3 will always be repelled from each other. Bars 1 and 3 will either be attracted to or repelled from each other, while bars 2 and 3 will always be attracted to each other.

Bar 1 and 3 will either be attracted to or repelled from each other, while bars 2 and 3 will always be attracted to each other.

Two particles, having the same charge but different velocities, are moving in a constant magnetic field (see the drawing, where the velocity vectors are drawn to scale). Which particle, if either, experiences the greater magnetic force? Particle 1 experiences the greater force, because it is moving perpendicular to the magnetic field. Particle 2 experiences the greater force, because it has the greater speed. Particle 2 experiences the greater force, because a component of its velocity is parallel to the magnetic field. Both particles experience the same magnetic force, because the component of each velocity that is perpendicular to the magnetic field is the same.

Both particles experience the same magnetic force, because the component of each velocity that is perpendicular to the magnetic field is the same.

Suppose that the positive charge in Figure 21.9a were launched from the negative plate toward the positive plate, in a direction opposite to the electric field Upper E Overscript right-arrow EndScripts. A sufficiently strong electric field would prevent the charge from striking the positive plate. Suppose that the positive charge in Figure 21.9b were launched from the south pole toward the north pole, in a direction opposite to the magnetic field Upper B Overscript right-arrow EndScripts. Would a sufficiently strong magnetic field prevent the charge from reaching the north pole? Yes. No, because a magnetic field cannot exert a force on a charged particle that is moving antiparallel to the field. No, because the magnetic force would cause the charge to move faster as it moved toward the north pole.

No, because a magnetic field cannot exert a force on a charged particle that is moving antiparallel to the field.

In a TV commercial that advertises a soda pop, a strong electromagnetic picks up a delivery truck carrying cans of the soft drink. The picture switches to the interior of the truck, where cans are seen to fly upward and stick to the roof just beneath the electromagnet. Are these cans made entirely of aluminum? No, because aluminum is more dense than iron. No, because aluminum is a non-ferromagnetic material. Yes, because iron is more dense than aluminum.

No, because aluminum is a non-ferromagnetic material

A positive charge moves along a circular path under the influence of a magnetic field. The magnetic field is perpendicular to the plane of the circle, as in Figure 21.11. If the velocity of the particle is reversed at some point along the path, will the particle retrace its path? Yes. No, because it will move around a different circle in a counterclockwise direction.

No, because it will move around a different circle in a counterclockwise direction.

Suppose that you accidentally use your left hand, instead of your right hand, to determine the direction of the magnetic force that acts on a positive charge moving in a magnetic field. Do you get the correct answer? Yes, because either hand can be used. No, because the direction you get will be perpendicular to the correct direction. No, because the direction you get will be opposite to the correct direction.

No, because the direction you get will be opposite to the correct direction.

A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant. If it is known that the external electric field is zero everywhere, then can you conclude that the external magnetic field is also zero? Ignore gravity. No, because the particle's acceleration isn't necessarily zero. No, because the particle could be moving parallel or anti-parallel to the direction of the magnetic field. Yes, because the particle's acceleration is zero.

No, because the particle could be moving parallel or anti-parallel to the direction of the magnetic field.

Review Conceptual Example 4 and Concept Simulation 21.1 as background for this question. Three particles move through a constant magnetic field and follow the paths shown in the drawing. Determine whether each particle is positively (+) charged, negatively (-) charged, or neutral. Particle 1 -; Particle 2 -; Particle 3 - Particle 1 +; Particle 2 +; Particle 3 + Particle 1 neutral; Particle 2 +; Particle 3 neutral Particle 1 +; Particle 2 neutral; Particle 3 - Particle 1 -; Particle 2 neutral; Particle 3 +

Particle 1 +; Particle 2 neutral; particle 3 -

There are four wires viewed end-on in the drawing. They are long, straight, and perpendicular to the plane of the paper. Their cross sections lie at the corners of a square. The magnitude of the current in each wire is the same. What must be the direction of the current in each wire (into or out of the page) so that when any single current is turned off, the total magnetic field at P (the center of the square) is directed toward a corner of the square? Wire 1: into; Wire 2: out of; Wire 3: into; Wire 4: into Wire 1: out of; Wire 2: out of; Wire 3: into; Wire 4: out of Wire 1: into; Wire 2: into; Wire 3: into; Wire 4: into Wire 1: out of; Wire 2: into; Wire 3: out of; Wire 4: out of

Wire 1-4: into

Suppose that the three particles in Figure 21.13a have identical charge magnitudes and masses. Which particle has the greatest speed? Refer to Conceptual Example 4 as needed. Particle 1 Particle 2 Particle 3

particle 3

If the earth's magnetism is assumed to originate from a large circular loop of current within the earth, the plane of the current loop must be oriented __________ to the earth's magnetic axis, and the direction of the current around the loop (when looking down on the loop from the north magnetic pole) is ____________. parallel, clockwise parallel, counterclockwise perpendicular, clockwise perpendicular, counterclockwise

perpendicular, clockwise

Refer to Figure 21.11. Assume that the particle in the picture is a proton. If an electron is projected at point 1 with the same velocity v Overscript right-arrow EndScripts, it will not follow exactly the same path as the proton, unless the magnetic field is adjusted in the following manner: the magnitude of the magnetic field must be ___________, and the direction of the magnetic field must be____________. the same, reversed increased, the same reduced, reversed

reduced, reversed

The drawing shows an end-on view of three parallel wires that are perpendicular to the plane of the paper. In two of the wires the current is directed into the paper, while in the remaining wire the current is directed out of the paper. Which way will the middle wire move? To the left To the right It will not move at all

to the left