Q: A moving charge $$q$$ with velocity $$\vec{v}$$ produces a magnetic field at a point located at $$\vec{r}$$ from the charge. Which equation correctly describes the magnetic field $$\vec{B} at $$that point?

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

Question 1

A moving charge $$q$$ with velocity $$\vec{v}$$ produces a magnetic field at a point located at $$\vec{r}$$ from the charge. Which equation correctly describes the magnetic field $$\vec{B} at $$that point?

Accepted Answer

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

Question 2

Which rule is used to determine the direction of the magnetic field produced by a moving positive charge?

Accepted Answer

Right-hand rule

Question 3

A straight wire carries a current $$I. $$What is the expression for the magnetic field $$B at a $$distance $$r$$ from the wire?

Accepted Answer

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

Question 4

Two parallel wires carry currents $$I_1$$ and $$I_2 in $$the same direction. What is the nature of the force between them?

Accepted Answer

They attract each other

Question 5

What is the formula for the force per unit length between two long, straight, parallel conductors separated by distance $$r$$ and carrying currents $$I_1$$ and $$I_2$$?

Accepted Answer

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

Question 6

A solenoid is used in an MRI machine to generate a uniform magnetic field. Which property of the solenoid is most important for achieving a strong, uniform field?

Accepted Answer

The number of turns per unit length

Question 7

What is the expression for the magnetic field at the center of a circular loop of radius $$a$$ carrying current $$I$$?

Accepted Answer

$$B = \frac{\mu_0$ I}{2a}$$

Question 8

Ampere’s law states that the line integral of the magnetic field around a closed path is proportional to:

Accepted Answer

The algebraic sum of the currents enclosed

Question 9

Which of the following best explains why computer cables produce little or no magnetic field?

Accepted Answer

Closely spaced wires carry current in both directions, canceling the fields

Question 10

The earth’s magnetic field is primarily caused by:

Accepted Answer

Currents circulating within its molten, conducting interior

Question 11

A cylindrical conductor of radius $$R$$ carries a current $$I$$ uniformly distributed over its cross-section. What is the magnetic field $$B at a $$distance $$r$$ from the axis, where $$r \u003c R$$?

Accepted Answer

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

Question 12

If the integration path in Ampere’s law does not enclose any current, what is the result of the line integral $$\oint \vec{B} \cdot d\vec{l}$$?

Accepted Answer

Zero

Question 13

A solenoid of length $$L$$ and $$N$$ turns carries a current $$I. $$What is the magnetic field inside the solenoid?

Accepted Answer

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

Question 14

Which scenario will result in the greatest magnetic field at the center of a square formed by four wires carrying equal currents?

Accepted Answer

Two wires carry current into the page, two out of the page

Question 15

What is the direction of the magnetic field produced by a current-carrying wire according to the right-hand rule?

Accepted Answer

In the direction your fingers curl when the thumb points along the current

Question 16

A current element $$Id\vec{l}$$ produces a magnetic field at a point $$\vec{r}$$ away. Which law describes this relationship?

Accepted Answer

Biot-Savart Law

Question 17

If two parallel wires carry equal currents in opposite directions, what is the force between them?

Accepted Answer

They repel each other

Question 18

A toroid is used to confine a magnetic field. Where is the magnetic field strongest?

Accepted Answer

Inside the space enclosed by the windings

Question 19

Which of the following is a real-world application of a strong, uniform magnetic field produced by a solenoid?

Accepted Answer

MRI (Magnetic Resonance Imaging)

Question 20

What is the SI definition of the ampere based on?

Accepted Answer

The force between two parallel wires

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