Q: The magnetic field at a point due to a moving point charge is given by which of the following equations?

$$ B(\vec{r}) = \frac{\mu_0$}{4\pi} \frac{q \vec{v} \times \hat{r}}{r^2$} $$

Q: The force on a charged particle moving in a magnetic field is given by which law?

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

Q: A magnetic dipole is placed in a uniform magnetic field. What is the direction of the torque acting on the dipole?

In the direction of $$\vec{\mu} \times \vec{B}$$

Question 1

Which of the following statements about electric and magnetic fields is correct?

Accepted Answer

All charges create electric fields, and only moving charges create magnetic fields.

Question 2

A glass sphere hangs by a thread. The north pole of a bar magnet is brought close to the sphere. What happens to the sphere?

Accepted Answer

It is unaffected by the bar magnet whether the sphere is charged or not.

Question 3

Which of the following best describes the direction of electric field lines?

Accepted Answer

They start at positive charges and end at negative charges.

Question 4

Which of the following is true about magnetic field lines?

Accepted Answer

They form closed loops and never terminate.

Question 5

A current-carrying loop is viewed from above. If the current flows counterclockwise, which side of the loop is the north pole?

Accepted Answer

North pole is on the top.

Question 6

The magnetic field at a point due to a moving point charge is given by which of the following equations?

Accepted Answer

$$ B(\vec{r}) = \frac{\mu_0$}{4\pi} \frac{q \vec{v} 	imes \hat{r}}{r^2$} $$

Question 7

For a long straight wire carrying current $$I$$, what is the magnitude of the magnetic field at a distance $$r$$ from the wire?

Accepted Answer

$$ B = \frac{\mu_0$ I}{2\pi r} $$

Question 8

A charged particle moves perpendicular to a uniform magnetic field. What is the shape of its trajectory?

Accepted Answer

Circle

Question 9

The force on a charged particle moving in a magnetic field is given by which law?

Accepted Answer

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

Question 10

A solenoid of length $$l$$ with $$N$$ turns and current $$I$$ produces a magnetic field inside given by:

Accepted Answer

$$ B = \frac{\mu_0$ N I}{l} $$

Question 11

Two long parallel wires carry currents in the same direction. What is the nature of the force between them?

Accepted Answer

They attract each other.

Question 12

A rectangular current loop is placed in a uniform magnetic field with the plane of the loop perpendicular to the field. What does the field exert on the loop?

Accepted Answer

A net torque.

Question 13

The magnetic dipole moment $$\vec{\mu} of a $$current loop of area $$A$$ and current $$I is $$given by:

Accepted Answer

$$ \vec{\mu} = I A $$

Question 14

Which of the following best describes ferromagnetic materials?

Accepted Answer

Their atomic magnetic moments tend to align in the same direction, forming domains.

Question 15

What is the direction of the force on a negative charge moving parallel to a current-carrying wire, due to the wire's magnetic field?

Accepted Answer

Into the screen

Question 16

The Hall effect can be used to determine which property of a material?

Accepted Answer

The density of charge carriers

Question 17

A magnetic dipole is placed in a uniform magnetic field. What is the direction of the torque acting on the dipole?

Accepted Answer

In the direction of $$\vec{\mu} 	imes \vec{B}$$

Question 18

Which of the following is a correct statement about the magnetic field inside a long solenoid?

Accepted Answer

It is uniform and parallel to the axis of the solenoid.

Question 19

A charged particle moves in a circle of radius $$r in a $$uniform magnetic field $$B. $$What is the expression for the cyclotron frequency?

Accepted Answer

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

Question 20

What is the main reason the aurora is observed near the Earth's poles?

Accepted Answer

The Earth's magnetic field directs charged particles into the atmosphere near the poles.

Magnetic Fields and Their Sources: Study Notes Ch 29

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