Q: A charged particle moves in a region with both electric field $$\vec{E}$$ and magnetic field $$\vec{B}. $$What is the total force acting on the particle?

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

Question 1

Which of the following statements about magnetic field lines is correct?

Accepted Answer

Magnetic field lines are closed loops that emerge from north poles and enter south poles.

Question 2

A charged particle moves with velocity $$\vec{v} in a $$region with a uniform magnetic field $$\vec{B}. $$What is the direction of the magnetic force acting on the particle?

Accepted Answer

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

Question 3

Which equation correctly expresses the magnetic force on a moving charge?

Accepted Answer

$$F_B = q(v 	imes B)$$

Question 4

A proton moves in a circle of radius $$r in a $$uniform magnetic field $$B. $$What is the correct expression for the radius of its path?

Accepted Answer

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

Question 5

A rectangular coil of wire with $$N$$ turns, area $$A$$, and current $$I is $$placed in a uniform magnetic field $$B. $$What is the magnitude of the maximum torque on the coil?

Accepted Answer

$$	au_{max} = N I A B$$

Question 6

Which of the following best describes the energy of a magnetic dipole in a magnetic field?

Accepted Answer

$$U = -\mu \cdot B$$

Question 7

A wire of length $$L$$ carries a current $$I in a $$uniform magnetic field $$B. $$The angle between the wire and the field is $$	heta. $$What is the magnitude of the force on the wire?

Accepted Answer

$$F = I L B \sin 	heta$$

Question 8

In a velocity selector, a charged particle moves through crossed electric and magnetic fields. If the electric field is $$E$$ and the magnetic field is $$B$$, what speed $$v$$ must the particle have to pass through undeflected?

Accepted Answer

$$v = E / B$$

Question 9

Which law states that the net magnetic flux through any closed surface is zero?

Accepted Answer

Gauss's Law for Magnetism

Question 10

A circular loop of radius $$r$$ lies in the $$xy-$$plane. A uniform magnetic field $$B$$ points along the $$+z$$ axis. What is the magnetic flux through the loop?

Accepted Answer

$$\Phi_B = B \pi r^2$

Question 11

Which of the following is true about the work done by magnetic forces on a moving charge?

Accepted Answer

Magnetic forces do no work on moving charges.

Question 12

A charged particle moves in a region with both electric field $$\vec{E}$$ and magnetic field $$\vec{B}. $$What is the total force acting on the particle?

Accepted Answer

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

Question 13

If a charged particle has a velocity component both perpendicular and parallel to a uniform magnetic field, what is the resulting path?

Accepted Answer

A helix

Question 14

The cyclotron frequency $$f$$ for a particle of charge $$q$$ and mass $$m in a $$magnetic field $$B is $$given by:

Accepted Answer

$$f = \dfrac{qB}{2\pi m}$$

Question 15

A wire segment of length $$dL$$ carries a current $$I in a $$uniform magnetic field $$B. $$What is the vector expression for the infinitesimal force on the segment?

Accepted Answer

$$dF = I (dL 	imes B)$$

Question 16

Which of the following is NOT a source of magnetic fields?

Accepted Answer

Magnetic monopoles

Question 17

A rectangular coil with $$N$$ turns, area $$A$$, and current $$I is $$placed in a uniform magnetic field $$B at an $$angle $$	heta to $$the field. What is the expression for its magnetic dipole moment?

Accepted Answer

$$\mu = N I A$$

Question 18

If a magnet is broken in half, what happens to its magnetic poles?

Accepted Answer

Each half retains both a north and a south pole.

Question 19

Which of the following best explains the evidence for magnetic pole reversals found on the ocean floor?

Accepted Answer

The orientation of iron-bearing minerals in the rock records the Earth's magnetic field at the time the rock solidified.

Magnetic Fields: Properties, Forces, and Applications

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