Q: A proton moves east with velocity $$v = 4.5 \times 10^6$ m/s and experiences a magnetic force due south of F = 8.0$$ \times $$10^{-14} N. $$What is the magnitude of the magnetic field?

$$B = \frac{F}{qv} = \frac{8.0 \times 10$$^{-14}$$}{(1.6 \times 10$$^{-19}$$)(4.5 \times 10^6$)} = 0.11 T$$

Q: A solenoid is 25 cm long, has 350 turns, and must produce a field of $$5.0 \times 10$$^{-5}$$ T. What current is required? (Use $$\$$mu_0 = 4$$\pi \times $$10^{-7} T$$·m/A)

$$I = \frac{B L}{\mu_0$ N} = \frac{5.0 \times 10$$^{-5}$$ \times 0.25}{4\pi \times 10$$^{-7}$$ \times 350} = 0.028 A$$

Q: An electron moves at $$2 \times 10^6$ m/s at an angle of 50$$^\circ$$ to a 400$ mT magnetic field. What is the magnitude of the force on the electron? (e = 1.6$$ \times $$10^{-19} C)$$

$$F = qvB\sin\theta = (1.6 \times 10$$^{-19}$$)(2 \times 10^6$)(0.4)\sin 50^\circ = 4.9 \times 10$$^{-14}$$ N

Q: A charge with $$q/m = 5.7 \times 10^7$ C/kg moves in a circle perpendicular to a 0.85$ T magnetic field. What is the period of revolution?

$$T = \frac{2\pi}{(q/m)B} = \frac{2\pi}{5.7 \times 10^7$ \times 0.85} = 1.3 \times 10$$^{-7}$$ s

Question 1

Which of the following statements best describes what happens when a bar magnet is broken in half?

Accepted Answer

Each piece becomes a new magnet with both a north and a south pole.

Question 2

Which of the following best describes the direction of magnetic field lines outside a bar magnet?

Accepted Answer

From the north pole to the south pole.

Question 3

A proton moves east with velocity $$v = 4.5 	imes 10^6$ m/s and experiences a magnetic force due south of F = 8.0$$ 	imes $$10^{-14} N. $$What is the magnitude of the magnetic field?

Accepted Answer

$$B = \frac{F}{qv} = \frac{8.0 	imes 10$$^{-14}$$}{(1.6 	imes 10$$^{-19}$$)(4.5 	imes 10^6$)} = 0.11 T$$

Question 4

Which rule is used to determine the direction of the magnetic force on a positive moving charge in a magnetic field?

Accepted Answer

Right-Hand Rule

Question 5

A wire carries a current $$I$$ perpendicular to a uniform magnetic field $$B. $$What is the magnitude of the force on a length $$L of $$the wire?

Accepted Answer

$$F = ILB$$

Question 6

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

Accepted Answer

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

Question 7

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

Accepted Answer

The magnetic force does no work on the charge.

Question 8

A solenoid is 25 cm long, has 350 turns, and must produce a field of $$5.0 	imes 10$$^{-5}$$ T. What current is required? (Use $$\$$mu_0 = 4$$\pi 	imes $$10^{-7} T$$·m/A)

Accepted Answer

$$I = \frac{B L}{\mu_0$ N} = \frac{5.0 	imes 10$$^{-5}$$ 	imes 0.25}{4\pi 	imes 10$$^{-7}$$ 	imes 350} = 0.028 A$$

Question 9

Two long, straight wires are separated by a distance $$r$$ and carry equal currents $$I in $$the same direction. What is the direction of the force between them?

Accepted Answer

The wires attract each other.

Question 10

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

Accepted Answer

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

Question 11

An electron moves at $$2 	imes 10^6$ m/s at an angle of 50$$^\circ$$ to a 400$ mT magnetic field. What is the magnitude of the force on the electron? (e = 1.6$$ 	imes $$10^{-19} C)$$

Accepted Answer

$$F = qvB\sin	heta = (1.6 	imes 10$$^{-19}$$)(2 	imes 10^6$)(0.4)\sin 50^\circ = 4.9 	imes 10$$^{-14}$$ N

Question 12

Which of the following best describes the magnetic field inside a long solenoid?

Accepted Answer

Strong and uniform

Question 13

A mass spectrometer separates ions based on which property?

Accepted Answer

Charge-to-mass ratio

Question 14

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

Accepted Answer

Upward (toward the top of the page)

Question 15

Which of the following is NOT a property of magnetic field lines?

Accepted Answer

They begin and end on electric charges.

Question 16

A current-carrying wire is placed in a uniform magnetic field. The force on the wire is maximum when the angle between the current and the field is:

Accepted Answer

$$90^\circ$$

Question 17

Two parallel wires carry currents in opposite directions. What is the nature of the force between them?

Accepted Answer

They repel each other.

Question 18

A charge with $$q/m = 5.7 	imes 10^7$ C/kg moves in a circle perpendicular to a 0.85$ T magnetic field. What is the period of revolution?

Accepted Answer

$$T = \frac{2\pi}{(q/m)B} = \frac{2\pi}{5.7 	imes 10^7$ 	imes 0.85} = 1.3 	imes 10$$^{-7}$$ s

Magnetism: Magnetic Fields, Forces, and Applications

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