Question 1

A positive charge moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$What is the direction of the magnetic force $$\vec{F}$$ acting on the charge?

Accepted Answer

Perpendicular to both $$\vec{v}$$ and $$\vec{B}$$

Question 2

Which equation gives the magnitude of the force on a charge $$q$$ moving with velocity $$\vec{v} at an $$angle $$	heta to a $$magnetic field $$\vec{B}$$?

Accepted Answer

$$F = qvB \sin 	heta$$

Question 3

A particle with mass $$m = 2.0\ 	ext{g}$$ and charge $$q = -2\ \mu	ext{C}$$ moves at $$v = 2000\ 	ext{m/s}$$ through a magnetic field $$B = 2.5\ 	ext{T} at an $$angle of $$30^\circ to $$the field. What is the magnitude of the acceleration?

Accepted Answer

$$a = \frac{qvB \sin 30^\circ}{m}$$

Question 4

If a charged particle moves in a straight line through a region of space, can you conclude that the magnetic field $$B is $$zero?

Accepted Answer

No, because if $$\vec{v} is $$parallel to $$\vec{B}$$, there is no magnetic force.

Question 5

What is the path of a charged particle moving perpendicular to a uniform magnetic field?

Accepted Answer

A circle

Question 6

Which of the following statements about the magnetic force is correct?

Accepted Answer

The magnetic force does no work on a particle.

Question 7

A current-carrying wire is placed in a magnetic field. Which right-hand rule is used to determine the direction of the magnetic field produced by the current?

Accepted Answer

Wrap fingers around wire with thumb pointing in direction of current; fingers curl in direction of $$\vec{B}$$

Question 8

An electron travels at $$1.5 	imes 10^7$\ 	ext{m/s}$$ perpendicular to a $$0.010\ 	ext{T}$$ magnetic field. What happens to its path if the field $$B is $$increased?

Accepted Answer

The radius of the path decreases.

Question 9

A positive charge $$+q$$ moves with velocity $$\vec{v} in a $$magnetic field $$\vec{B} as $$shown. What is the direction of the magnetic force?

Accepted Answer

Into the page

Question 10

Which equation describes the radius $$R of $$the circular path for a particle of mass $$m$$, charge $$q$$, and velocity $$v in a $$magnetic field $$B$$?

Accepted Answer

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

Question 11

A cosmic ray proton enters Earth's magnetic field and follows a helical path. What causes the helical motion?

Accepted Answer

The proton's velocity has both perpendicular and parallel components to $$\vec{B}$$

Question 12

Which of the following is NOT a consequence of the magnetic force being perpendicular to the displacement?

Accepted Answer

The magnetic field does work on the particle

Question 13

A wire carrying current $$I is $$placed in a magnetic field $$\vec{B}. $$What is the equation for the force per unit length between two parallel wires separated by distance $$d$$?

Accepted Answer

$$\frac{F}{L} = \frac{\mu_0$ I_1$ I_2$}{2\pi d}$$

Question 14

A negative charge $$-q$$ moves with velocity $$\vec{v} in a $$magnetic field $$\vec{B}. $$How does the direction of the force compare to that for a positive charge?

Accepted Answer

It is opposite to that for a positive charge.

Question 15

Which right-hand rule is used to determine the direction of the force on a positive charge moving in a magnetic field?

Accepted Answer

Point fingers in direction of velocity, curl toward $$\vec{B}$$; thumb points toward force

Question 16

A charged particle moves with velocity $$\vec{v}$$ parallel to a magnetic field $$\vec{B}. $$What is the force on the particle?

Accepted Answer

$$F = 0$$

Question 17

An electron experiences a force of $$6.2 	imes 10$$^{-13}$$\ 	ext{N}$$ while moving northward at $$2.8 	imes 10^6$\ 	ext{m/s} in a $$magnetic field. The force is vertically upward. What is the magnitude of the magnetic field?

Accepted Answer

$$B = \frac{F}{qv}$$

Question 18

Which of the following best describes the motion of a charged particle in Earth's magnetic field?

Accepted Answer

It follows a spiral path around the field lines.

Question 19

A wire carrying current upward is placed in a magnetic field pointing east. What is the direction of the force on the wire?

Accepted Answer

North

Force on Electric Charge Moving in a Magnetic Field (Chapter 20 Study Notes)

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