Q: A wire carrying current $$I is $$placed in a uniform magnetic field $$\vec{B}. $$What is the vector expression for the force on a straight segment of length $$\vec{l}$$?

$$\vec{F} = I \vec{l} \times \vec{B}$$

Question 1

Which statement best describes the behavior of magnetic poles when a bar magnet is broken in half?

Accepted Answer

Each half forms a new magnet with both a north and a south pole.

Question 2

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

Accepted Answer

$$F = 0$$

Question 3

A positive charge $$q$$ moves perpendicular to a magnetic field $$\vec{B}. $$What is the direction of the force acting on the charge?

Accepted Answer

Perpendicular to both $$\vec{v}$$ and $$\vec{B}$$, given by the right-hand rule

Question 4

Which equation gives the magnitude of the magnetic force on a charge $$q$$ moving at velocity $$\vec{v} at an $$angle $$\phi to a $$magnetic field $$\vec{B}$$?

Accepted Answer

$$F = qvB \sin \phi$$

Question 5

A wire carrying current $$I is $$placed in a uniform magnetic field $$\vec{B}. $$What is the vector expression for the force on a straight segment of length $$\vec{l}$$?

Accepted Answer

$$\vec{F} = I \vec{l} 	imes \vec{B}$$

Question 6

What is the SI unit of magnetic field $$B$$?

Accepted Answer

Tesla (T)

Question 7

A charged particle moves in a region where both electric field $$\vec{E}$$ and magnetic field $$\vec{B}$$ are present and perpendicular. What speed $$v$$ allows the particle to pass through undeflected?

Accepted Answer

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

Question 8

Which statement about magnetic field lines is correct?

Accepted Answer

Magnetic field lines are tangent to the direction of $$\vec{B} at $$each point.

Question 9

A proton moves in a circle of radius $$R in a $$uniform magnetic field $$B. $$Which equation relates the radius to the proton's mass $$m$$, speed $$v$$, and charge $$q$$?

Accepted Answer

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

Question 10

What is the angular frequency $$\omega of a $$charged particle moving in a circle in a uniform magnetic field $$B$$?

Accepted Answer

$$\omega = \frac{|q|B}{m}$$

Question 11

A current loop of area $$A$$ and current $$I is $$placed in a uniform magnetic field $$B. $$What is the magnitude of the torque $$	au on $$the loop when the normal to the loop makes an angle $$\phi$$ with $$\vec{B}$$?

Accepted Answer

$$	au = IAB \sin \phi$$

Question 12

What is the expression for the magnetic dipole moment $$\vec{\mu} of a $$current loop with current $$I$$ and area $$A$$?

Accepted Answer

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

Question 13

Which equation gives the magnetic flux $$\Phi_B$$ through a surface?

Accepted Answer

$$\Phi_B = \int \vec{B} \cdot d\vec{A}$$

Question 14

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

Accepted Answer

$$\int \vec{B} \cdot d\vec{A} = 0$$

Question 15

A charged particle moves in a helical path in a uniform magnetic field. Which component of its velocity remains constant?

Accepted Answer

The component parallel to $$\vec{B}$$

Question 16

In a velocity selector, what condition must be met for a charged particle to pass through undeflected?

Accepted Answer

$$qE = qvB$$

Question 17

What is the potential energy $$U of a $$magnetic dipole moment $$\vec{\mu} in a $$magnetic field $$\vec{B}$$?

Accepted Answer

$$U = -\vec{\mu} \cdot \vec{B}$$

Question 18

Which of the following best explains why the Earth's north geographic pole is close to a magnetic south pole?

Accepted Answer

The north pole of a compass needle points toward the Earth's magnetic south pole.

Question 19

A straight wire segment of length $$l$$ carries a current $$I$$ and is placed at an angle $$\phi to a $$uniform magnetic field $$B. $$What is the magnitude of the force on the wire?

Accepted Answer

$$F = I l B \sin \phi$$

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