102-163, 80-101

A straight wire carrying a current 𝐼 is in a uniform magnetic field that is directed out of the page, as shown in the figure. Which of the following best illustrates the direction of the magnetic force on the wire?

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• zero

A bar magnet and a wire loop carrying current I are arranged as shown above. In which direction, if any, is the force on the current loop due to the magnet?

• Toward the magnet

• Away from the magnet

• Toward the top of the page

• Toward the bottom of the page

• There is no force on the current loop.

A particle of electric charge +Q and mass m initially moves along a straight line in the plane of the page with constant speed v, as shown above. The particle enters a uniform magnetic field of magnitude B directed out of the page and moves in a semicircular arc of radius R.

Question

Which of the following best indicates the magnitude and the direction of the magnetic force 𝐹→ on the charge just after the charge enters the magnetic field?

• Magnitude: 𝑘𝑄^2/𝑅^2
  Direction: Toward the top of the page

• Magnitude: 𝑘𝑄^2/𝑅^2
  Direction: Toward the bottom of the page

• Magnitude: QvB
  Direction: Out of the plane of the page

• Magnitude: QvB
  Direction: Toward the top of the page

• Magnitude: QvB
  Direction: Toward the bottom of the page

Answer explanation

A particle of electric charge +Q and mass m initially moves along a straight line in the plane of the page with constant speed v, as shown above. The particle enters a uniform magnetic field of magnitude B directed out of the page and moves in a semicircular arc of radius R.

Question

If the magnetic field strength is increased, which of the following will be true about the radius R?

1. I. R increases if the incident speed is held constant.

2. II. For R to remain constant, the incident speed must be increased.

3. III. For R to remain constant, the incident speed must be decreased.

• I only

• II only

• III only

• I and II only

• I and III only

Answer explanation

the correct answer for the next question is the first option

Two long, straight, current-carrying wires are parallel to each other in the plane of the page and separated by a distance a, as shown above. The direction of the current I in each wire is toward the top of the page. Which of the following best represents the force per unit length acting on the wires?

• Zero

A Gaussian cube with sides of length 𝑠 encloses a single point charge +𝑄. The electric flux through one face of the cube is

• 0

Charge is distributed uniformly throughout a long nonconducting cylinder of radius R. Which of the following graphs best represents the magnitude of the resulting electric field E as a function of r, the distance from the axis of the cylinder?

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A solid metallic sphere of radius R has charge Q uniformly distributed on its outer surface. A graph of electric potential V as a function of position r is shown above. Which of the following graphs best represents the magnitude of the electric field E as a function of position r for this sphere?

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Two charged particles, each with a charge of +q, are located along the x-axis at x = 2 and x = 4, as shown above. Which of the following shows the graph of the magnitude of the electric field along the x-axis from the origin to x = 6?

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The nonconducting hollow sphere of radius R shown above carries a large charge +Q, which is uniformly distributed on its surface. There is a small hole in the sphere. A small charge +q is initially located at point P, a distance r from the center of the sphere. If k = 1/4𝛑𝛜₀ , what is the work that must be done by an external agent in moving the charge +q from P through the hole to the center O of the sphere?

• zero

• kqQ/r

• kqQ/R

• kq(Q-q)/r

• kqQ(1/R-1/r)