Q: What is the SI unit of magnetic field, and how is it related to the Gauss?

The SI unit is the Tesla (T), and $$1 \text{T} = 10^4$ \text{G}.$$

Q: If a charged particle moves in both electric and magnetic fields, what is the expression for the total force acting on it?

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

Question 1

Which of the following statements best describes the difference between electric and magnetic fields regarding the force they exert on a charged particle?

Accepted Answer

The electric force acts along the direction of the electric field and can do work, while the magnetic force acts perpendicular to the magnetic field and cannot do work.

Question 2

A charged particle with charge $$q$$ moves with velocity $$\vec{v} in a $$magnetic field $$\vec{B}. $$What is the magnitude of the magnetic force if the angle between $$\vec{v}$$ and $$\vec{B} is$$ $$\phi$$?

Accepted Answer

$$F = qvB \sin \phi$$

Question 3

If a charged particle moves parallel to a magnetic field, what is the magnetic force acting on it?

Accepted Answer

$$F = 0$$

Question 4

A proton and an electron are moving with the same velocity in a uniform magnetic field. How do their magnetic forces compare?

Accepted Answer

The forces are equal in magnitude but opposite in direction.

Question 5

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

Accepted Answer

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

Question 6

Which of the following best describes the behavior of magnetic field lines around a bar magnet?

Accepted Answer

They form closed loops, exiting the north pole and entering the south pole outside the magnet.

Question 7

A wire of length $$L$$ carrying current $$I is $$placed in a uniform magnetic field $$B at an $$angle $$	heta to $$the field. What is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB \sin 	heta$$

Question 8

Which of the following is true about magnetic monopoles?

Accepted Answer

They have never been detected; magnetic poles always occur in pairs.

Question 9

A mass spectrometer uses a velocity selector where electric and magnetic fields are perpendicular. What speed $$v$$ must a particle have to pass through undeflected?

Accepted Answer

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

Question 10

What is the SI unit of magnetic field, and how is it related to the Gauss?

Accepted Answer

The SI unit is the Tesla (T), and $$1 	ext{T} = 10^4$ 	ext{G}.$$

Question 11

A rectangular current loop of area $$A$$ carries current $$I in a $$uniform magnetic field $$B. $$What is the maximum torque $$	au_{max} on $$the loop?

Accepted Answer

$$	au_{max} = IAB$$

Question 12

Which of the following is a correct statement about the Hall effect?

Accepted Answer

It can be used to determine the sign and density of charge carriers in a conductor.

Question 13

A charged particle moves in a helical path in a uniform magnetic field. Which component of its velocity determines the radius of the helix?

Accepted Answer

The component perpendicular to the magnetic field.

Question 14

What is the magnetic flux $$\Phi_B$$ through a flat surface of area $$A$$ when the magnetic field $$B$$ makes an angle $$	heta$$ with the normal to the surface?

Accepted Answer

$$\Phi_B = BA \cos 	heta$$

Question 15

According to Gauss' law for magnetism, what is the net magnetic flux through any closed surface?

Accepted Answer

It is always zero.

Question 16

A cyclotron accelerates charged particles using a combination of electric and magnetic fields. Why does the period of revolution remain constant as the particle's speed increases (non-relativistic case)?

Accepted Answer

Because the period depends only on the mass and charge of the particle and the magnetic field, not on speed.

Question 17

A current-carrying wire is placed in a uniform magnetic field. Which rule is used to determine the direction of the force on the wire?

Accepted Answer

Right-hand rule

Question 18

If a charged particle moves in both electric and magnetic fields, what is the expression for the total force acting on it?

Accepted Answer

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

Question 19

Which of the following is true about the work done by a magnetic force on a moving charged particle?

Accepted Answer

The magnetic force does no work on the particle.

Magnetic Fields and Magnetic Forces: Study Notes

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