Q: What is the expression for the magnetic force on a moving charge $$q$$ with velocity $$\vec{v} in a $$magnetic field $$\vec{B}$$?

$$\vec{F} = q\vec{v} \times \vec{B}$$

Question 1

Two long, straight, parallel wires carry currents $$I_1$$ and $$I_2 in $$the same direction and are separated by a distance $$d. $$What is the direction of the force on wire 1 due to wire 2?

Accepted Answer

Perpendicular to both wires, pointing toward wire 2

Question 2

If the currents in two parallel wires are in opposite directions, what is the nature of the force between them?

Accepted Answer

The wires repel each other

Question 3

A square current loop of side $$a$$ carries a current $$I$$ and is placed in a uniform magnetic field $$B. $$What is the magnitude of the torque on the loop if the plane of the loop makes an angle $$	heta$$ with the magnetic field?

Accepted Answer

$$	au = I a^2$ B \sin	heta$$

Question 4

Which of the following best explains why a ferromagnetic material can become a permanent magnet after being exposed to an external magnetic field?

Accepted Answer

Some magnetic domains remain aligned after the external field is removed

Question 5

What is the direction of the magnetic field at the center of a circular loop carrying current $$I$$ using the right-hand rule?

Accepted Answer

Along the axis of the loop, in the direction of the right thumb when fingers curl with the current

Question 6

A charged particle moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$What is the resulting motion of the particle?

Accepted Answer

It moves in a circular path with radius $$r = \frac{mv}{qB}$$

Question 7

Which equation gives the magnetic field at a distance $$r$$ from a long, straight wire carrying current $$I$$?

Accepted Answer

$$B = \frac{\mu_0$ I}{2\pi r}$$

Question 8

What is the magnetic force on a straight segment of wire of length $$L$$ carrying current $$I in a $$uniform magnetic field $$B$$, if the wire is perpendicular to the field?

Accepted Answer

$$F = ILB$$

Question 9

Which of the following statements about the magnetic properties of most elements is correct?

Accepted Answer

Their atomic magnetic moments are randomly arranged, resulting in nearly zero net magnetism

Question 10

A ferromagnetic material is placed near a solenoid carrying current. What happens to the domains inside the material?

Accepted Answer

They align with the solenoid's magnetic field

Question 11

Which law is used to calculate the magnetic field produced by a moving point charge?

Accepted Answer

Biot-Savart law

Question 12

What is the expression for the magnetic force on a moving charge $$q$$ with velocity $$\vec{v} in a $$magnetic field $$\vec{B}$$?

Accepted Answer

$$\vec{F} = q\vec{v} 	imes \vec{B}$$

Question 13

A current loop in a uniform magnetic field experiences a net torque but no net force. Why?

Accepted Answer

The forces on opposite sides of the loop are equal and opposite, canceling out

Question 14

Which of the following best describes the magnetic dipole moment of an electron?

Accepted Answer

It is due to the electron's orbital motion and intrinsic spin

Question 15

What happens to the net magnetic dipole moment of a ferromagnetic object after it is removed from an external magnetic field?

Accepted Answer

It may remain nonzero if some domains stay aligned

Question 16

Which of the following is a correct application of Ampère’s law?

Accepted Answer

Calculating the magnetic field inside a long solenoid

Question 17

A simple electric motor works because:

Accepted Answer

A current-carrying loop in a magnetic field experiences a torque that causes rotation

Question 18

Which of the following statements about the right-hand rule is correct?

Accepted Answer

Point your thumb in the direction of current, and your fingers curl in the direction of the magnetic field

Question 19

A charged particle moves parallel to a uniform magnetic field. What is the magnetic force on the particle?

Accepted Answer

Zero

Magnetic Forces, Current-Carrying Wires, and Magnetic Properties of Matter

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