Q: The magnitude of the magnetic force on a straight wire of length $$l$$ carrying current $$I in a $$uniform magnetic field $$\vec{B} is $$given by which of the following equations?

$$F_{\text{wire}} = I l B \sin \alpha$$

Question 1

A charged particle moves in a circular path in a bubble chamber with a uniform magnetic field directed into the page. If the particle's path curves counterclockwise, what can you conclude about the charge of the particle?

Accepted Answer

The particle is positively charged.

Question 2

The magnitude of the magnetic force on a straight wire of length $$l$$ carrying current $$I in a $$uniform magnetic field $$\vec{B} is $$given by which of the following equations?

Accepted Answer

$$F_{	ext{wire}} = I l B \sin \alpha$$

Question 3

A horizontal wire carries a current to the right in a region where the magnetic field points into the page. What is the direction of the force on the wire?

Accepted Answer

Up

Question 4

Two parallel wires carry equal currents in opposite directions. What is the direction of the force on the left wire due to the right wire?

Accepted Answer

To the right

Question 5

A square loop of wire carrying current in the counterclockwise direction is placed in a uniform magnetic field pointing to the right. Which of the following statements is correct?

Accepted Answer

The net force on the loop is zero.

Question 6

A magnetic dipole moment $$\vec{m} is $$placed in a uniform magnetic field $$\vec{B}. In $$which orientation is the potential energy of the system lowest?

Accepted Answer

$$\vec{m} is $$parallel to $$\vec{B}$$

Question 7

Which of the following best describes a ferromagnetic material?

Accepted Answer

A material in which atomic magnetic dipole moments align over a large domain and tend to remain aligned.

Question 8

A wire of length $$l$$ moves with speed $$v$$ perpendicular to a uniform magnetic field $$B. $$What is the motional emf induced between the ends of the wire?

Accepted Answer

$$\mathcal{E} = v l B$$

Question 9

A long straight wire is oriented vertically and is moving to the right in a region where a uniform magnetic field points into the page. In what direction do the electrons in the wire experience a magnetic force?

Accepted Answer

Up the page

Question 10

A loop of wire moves to the right and enters a region with a uniform magnetic field directed into the page. At the instant the right side of the loop enters the field, what is the direction of the induced current in the loop?

Accepted Answer

Counterclockwise

Question 11

A square loop of area $$A is $$fully within a region of uniform magnetic field $$B. $$What is the magnetic flux through the loop if the field is perpendicular to the plane of the loop?

Accepted Answer

$$\Phi_B = B A$$

Question 12

According to Lenz's Law, the direction of the induced current in a closed loop is such that:

Accepted Answer

It opposes the change in magnetic flux through the loop.

Question 13

A conducting ring is oriented with its axis to the right. A bar magnet is moved to the left of the ring. What is the direction of the induced current at the top of the ring?

Accepted Answer

Into the page

Question 14

A metal tube is held vertically and a magnet is dropped down the tube. The magnet falls more slowly than a non-magnetic metal. What is the primary reason for this?

Accepted Answer

Induced currents in the tube create a magnetic field that opposes the motion of the magnet.

Question 15

Which of the following statements about the emf induced in a rotating loop of area $$A at $$constant angular speed $$\omega in a $$uniform magnetic field $$B is $$correct?

Accepted Answer

If $$B$$ was greater, the emf would be greater.

Question 16

A ground fault circuit interrupter (GFCI) detects a ground fault by:

Accepted Answer

Sensing a difference in current between the two wires, which causes a change in magnetic flux.

Question 17

A rectangular loop of width $$w$$ and height $$h is $$moving to the right at constant speed $$v$$ and enters a region of uniform magnetic field $$B. At $$the moment the loop is entering the field, which of the following changes would increase the induced emf?

Accepted Answer

Increasing $$h or$$ $$v$$

Question 18

An induction stove heats a pan by:

Accepted Answer

Inducing eddy currents in the pan, which heat it due to resistance.

Question 19

A metal detector works by:

Accepted Answer

Detecting changes in magnetic fields caused by eddy currents in nearby conductors.

Magnetic Forces, Current-Carrying Wires, and Electromagnetic Induction ch 30

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