Q: Which of the following correctly expresses the magnetic force on a charged particle moving in a magnetic field?

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

Q: Which of the following is NOT a Maxwell equation?

$$\nabla \cdot \vec{E} = \vec{B}$$

Question 1

Which of the following correctly expresses the magnetic force on a charged particle moving in a magnetic field?

Accepted Answer

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

Question 2

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

Accepted Answer

No force acts on the proton

Question 3

Which equation describes the work done by the magnetic force on a charged particle?

Accepted Answer

$$W = 0$$

Question 4

A negative charge moves to the right in a region where the magnetic field points into the page. What is the direction of the magnetic force on the charge?

Accepted Answer

Downward

Question 5

Which of the following is the correct formula for the magnitude of the magnetic force on a particle with charge $$q$$ moving at speed $$v$$ perpendicular to a magnetic field $$B$$?

Accepted Answer

$$F = |q|vB$$

Question 6

A mass spectrometer separates ions based on their mass. If two ions have the same charge and velocity but different masses, which ion will follow a path with a larger radius?

Accepted Answer

The ion with larger mass

Question 7

In a velocity selector, the electric and magnetic fields are perpendicular. What is the condition for a charged particle to pass through undeflected?

Accepted Answer

$$v = \frac{E}{B}$$

Question 8

A beam of singly ionized uranium atoms ($$^{235}U$$ and $$^{238}U) is $$injected into a mass spectrometer. The $$^{238}U$$ ions follow a trajectory illustrated. Where will the $$^{235}U$$ ions strike the collecting plate?

Accepted Answer

Above the $$^{238}U$$ ions

Question 9

If the magnetic field strength in a mass spectrometer is increased, what happens to the spacing between where $$^{235}U$$ and $$^{238}U$$ ions strike?

Accepted Answer

The spacing decreases

Question 10

Which of the following is NOT a property of antimatter compared to matter?

Accepted Answer

Different mass

Question 11

What is the expression for centripetal acceleration for a particle moving in a circle of radius $$R$$ with speed $$v$$?

Accepted Answer

$$a_c = \frac{v^2$}{R}$$

Question 12

Which of the following is a correct statement about the work done by the magnetic force on a moving charge?

Accepted Answer

The magnetic force does no work

Question 13

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

Accepted Answer

$$R = \frac{mv}{|q|B}$$

Question 14

Which of the following is a consequence of the Lorentz force law $$\vec{F} = Q(\vec{E} + \vec{v} 	imes \vec{B})$$?

Accepted Answer

A moving charge in a magnetic field experiences a force perpendicular to its velocity

Question 15

Which of the following is NOT a Maxwell equation?

Accepted Answer

$$
abla \cdot \vec{E} = \vec{B}$$

Question 16

In a cloud chamber experiment, pair creation is observed. Which equation relates the energy required for pair creation to the mass of the created particles?

Accepted Answer

$$E = mc^2$

Question 17

A velocity selector uses perpendicular electric and magnetic fields. If the net force on a particle is zero, what can be said about its velocity?

Accepted Answer

It is constant

Question 18

Which of the following best describes the path of a charged particle moving perpendicular to a uniform magnetic field?

Accepted Answer

Circular

Question 19

In Thomson’s $$e/m$$ experiment, what is the purpose of the velocity selector?

Accepted Answer

To select particles with a specific velocity

Guidance on Magnetic Force Direction for Charged Particles

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