Q: The force on a straight wire of length $$l$$ carrying current $$I in a $$uniform magnetic field $$\vec{B} is $$given by which equation?

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

Question 1

Which of the following statements about magnetic poles is correct?

Accepted Answer

Like magnetic poles repel each other, and unlike poles attract.

Question 2

A straight wire carries a current $$I$$ vertically upward. What is the direction of the magnetic field produced by the wire at a point directly east of the wire?

Accepted Answer

North

Question 3

The force on a straight wire of length $$l$$ carrying current $$I in a $$uniform magnetic field $$\vec{B} is $$given by which equation?

Accepted Answer

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

Question 4

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

Accepted Answer

$$F = qvB$$

Question 5

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

Accepted Answer

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

Question 6

Which of the following best describes why a magnetic field cannot do work on a charged particle?

Accepted Answer

The magnetic force is always perpendicular to the velocity of the particle.

Question 7

A velocity selector uses perpendicular electric and magnetic fields to select particles of a specific velocity. What is the condition for a particle to pass through undeflected?

Accepted Answer

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

Question 8

A current loop of area $$A$$ and current $$I is $$placed in a uniform magnetic field $$B. $$What is the maximum torque experienced by the loop?

Accepted Answer

$$	au_{max} = IAB$$

Question 9

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

Accepted Answer

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

Question 10

In a loudspeaker, how is electrical energy converted into sound?

Accepted Answer

A current in the coil creates a force due to the magnetic field, moving the cone and producing sound waves.

Question 11

A mass spectrometer uses a velocity selector and a magnetic field to separate ions. If the velocity selector has $$E = 2.0 	imes 10^4$ V/m and B = 0.50$ T, what velocity will pass through undeflected?

Accepted Answer

$$1.0 	imes 10^4$ m/s

Question 12

A wire of length $$0.5 m $$carries a current of $$2 A $$perpendicular to a uniform magnetic field of $$0.3 T. $$What is the magnitude of the force on the wire?

Accepted Answer

$$0.15 N$$

Question 13

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

Accepted Answer

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

Question 14

Which of the following is true about the direction of the magnetic dipole moment $$\vec{\mu}$$ for a current loop?

Accepted Answer

It is perpendicular to the plane of the loop, in the direction given by the right-hand rule.

Question 15

A negative charge moves to the right in a magnetic field directed into the page. What is the direction of the force on the charge?

Accepted Answer

Downward

Question 16

Which of the following best explains why the commutator is necessary in a DC motor?

Accepted Answer

It reverses the current direction in the coil every half turn to keep the torque in the same direction.

Question 17

A particle with charge $$q$$ and mass $$m$$ enters a region with a uniform magnetic field $$B at $$velocity $$v$$ perpendicular to $$B. $$What is the period $$T of $$its circular motion?

Accepted Answer

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

Question 18

Which of the following is a correct unit for the magnetic field $$B$$?

Accepted Answer

Tesla (T)

Question 19

A rectangular current loop is placed in a uniform magnetic field. In which orientation is the potential energy of the loop minimized?

Accepted Answer

When the magnetic dipole moment is parallel to the magnetic field.

Question 20

Which of the following best describes the operation of a mass spectrometer?

Accepted Answer

It separates ions based on their mass-to-charge ratio using electric and magnetic fields.

Magnetism: Magnetic Forces, Fields, and Applications

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