Q: A proton moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B} of $$magnitude $$B = \frac{A}{100} T. If $$the velocity is $$B \times 10^6$ m/s, what is the magnitude of the magnetic force acting on the proton?

$$F = qvB = (1.6 \times 10$$^{-19}$$) \times (B \times 10^6$) \times \frac{A}{100}$$

Q: A wire of length $$L = 0.25 m $$carries a current $$I = \frac{A}{5} A in a $$magnetic field $$B = \frac{A}{100} T. $$What is the magnitude of the force on the wire?

$$F = ILB = \frac{A}{5} \times 0.25 \times \frac{A}{100}$$

Q: Which equation correctly describes the magnetic force on a moving charge in a magnetic field?

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

Q: A wire carrying current $$I is $$placed in a magnetic field $$\vec{B}. $$Which equation gives the force on the wire?

$$\vec{F} = I\vec{L} \times \vec{B}$$

Question 1

A proton moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B} of $$magnitude $$B = \frac{A}{100} T. If $$the velocity is $$B 	imes 10^6$ m/s, what is the magnitude of the magnetic force acting on the proton?

Accepted Answer

$$F = qvB = (1.6 	imes 10$$^{-19}$$) 	imes (B 	imes 10^6$) 	imes \frac{A}{100}$$

Question 2

In the scenario shown in image (a), a current $$I$$ flows upward in a wire placed in a magnetic field $$B_{out} ($$out of the page). What is the direction of the magnetic force on the wire?

Accepted Answer

To the left

Question 3

A wire of length $$L = 0.25 m $$carries a current $$I = \frac{A}{5} A in a $$magnetic field $$B = \frac{A}{100} T. $$What is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB = \frac{A}{5} 	imes 0.25 	imes \frac{A}{100}$$

Question 4

In image (b), a current flows upward and the magnetic field points to the right. Using the right-hand rule, what is the direction of the force on the wire?

Accepted Answer

Out of the page

Question 5

An electron moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$How does the direction of the magnetic force compare to that of a proton under the same conditions?

Accepted Answer

The force is in the opposite direction to that of the proton

Question 6

A neutron moves with velocity $$\vec{v} in a $$magnetic field $$\vec{B}. $$What is the magnetic force acting on the neutron?

Accepted Answer

Zero, because the neutron has no charge

Question 7

In image (c), a current flows to the left in a wire placed in a magnetic field $$B_{in} ($$into the page). What is the direction of the magnetic force on the wire?

Accepted Answer

Upward

Question 8

A positive particle enters a region where the magnetic field is out of the page and its velocity is along the $$+x$$ direction. What path does the particle follow?

Accepted Answer

It curves upward in a circular path

Question 9

A negative particle enters a region where the magnetic field is out of the page and its velocity is along the $$+x$$ direction. What path does the particle follow?

Accepted Answer

It curves downward in a circular path

Question 10

A neutral particle enters a region where the magnetic field is out of the page and its velocity is along the $$+x$$ direction. What path does the particle follow?

Accepted Answer

It moves straight

Question 11

Which equation correctly describes the magnetic force on a moving charge in a magnetic field?

Accepted Answer

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

Question 12

A wire carrying current $$I is $$placed in a magnetic field $$\vec{B}. $$Which equation gives the force on the wire?

Accepted Answer

$$\vec{F} = I\vec{L} 	imes \vec{B}$$

Question 13

If a wire is oriented parallel to the magnetic field, what is the magnetic force on the wire?

Accepted Answer

Zero, because $$\vec{L}$$ and $$\vec{B}$$ are parallel

Question 14

A proton moves in a circle in a magnetic field. What is the expression for its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{qvB}{m}$$

Question 15

Which of the following best describes the right-hand rule for determining the direction of magnetic force on a positive charge?

Accepted Answer

Point your fingers in the direction of velocity, curl them toward the magnetic field, and your thumb points in the direction of force

Question 16

A wire of length $$L$$ carries a current $$I$$ perpendicular to a magnetic field $$B. If $$the current is doubled, what happens to the magnetic force?

Accepted Answer

The force doubles

Question 17

A particle with charge $$q$$ and mass $$m$$ moves with velocity $$v$$ perpendicular to a magnetic field $$B. $$What is the radius of its circular path?

Accepted Answer

$$r = \frac{mv}{qB}$$

Question 18

If a wire is placed in a magnetic field and the current is reversed, what happens to the direction of the magnetic force?

Accepted Answer

The force reverses direction

Question 19

A wire carrying current $$I is $$placed in a magnetic field $$B at an $$angle $$	heta to $$the field. What is the expression for the force?

Accepted Answer

$$F = ILB \sin 	heta$$

Magnetic Force and Motion of Charged Particles in Magnetic Fields

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