Q: A wire carries a current of $$I = 25\ \mathrm{A}$$ straight up. What is the magnitude of the magnetic field $$B at a $$point $$r = 0.10\ \mathrm{m}$$ away from the wire? Use $$\mu_0$ = 4\pi \times 10$$^{-7}$$\ \mathrm{T\cdot m/A}.$$

$$B = 5.0 \times 10$$^{-5}$$\ \mathrm{T}$$

Q: A solenoid is $$0.5\ \mathrm{m}$$ long, has $$N = 1000$$ turns, and carries a current $$I = 2\ \mathrm{A}. $$What is the magnitude of the magnetic field inside the solenoid?

$$B = 8.0 \times 10$$^{-3}$$\ \mathrm{T}$$

Q: Two parallel wires, each $$2\ \mathrm{m}$$ long and $$3\ \mathrm{mm}$$ apart, carry currents of $$8\ \mathrm{A} in $$opposite directions. What is the magnitude of the force between them?

$$F = 8.5 \times 10$$^{-4}$$\ \mathrm{N}$$

Q: A circular loop of wire with $$N = 10$$ turns, diameter $$d = 0.10\ \mathrm{m}$$, and current $$I = 3\ \mathrm{A} is $$placed in a $$2\ \mathrm{T}$$ magnetic field. What is the maximum torque experienced by the loop?

$$\tau_{max} = 0.24\ \mathrm{N\cdot m}$$

Question 1

Which statement best describes what happens when a bar magnet is cut in half?

Accepted Answer

Each half becomes a smaller magnet with both a north and a south pole.

Question 2

A wire carries a current of $$I = 25\ \mathrm{A}$$ straight up. What is the magnitude of the magnetic field $$B at a $$point $$r = 0.10\ \mathrm{m}$$ away from the wire? Use $$\mu_0$ = 4\pi 	imes 10$$^{-7}$$\ \mathrm{T\cdot m/A}.$$

Accepted Answer

$$B = 5.0 	imes 10$$^{-5}$$\ \mathrm{T}$$

Question 3

Which of the following is true about the Earth's magnetic field?

Accepted Answer

The Earth's 'North Magnetic Pole' is actually a magnetic south pole.

Question 4

A proton moves upward and experiences a force to the west in a magnetic field. What is the direction of the magnetic field?

Accepted Answer

North

Question 5

A rectangular loop of wire hangs partway into a magnetic field directed out of the board. The bottom length of wire is $$0.10\ \mathrm{m}$$, and the current is $$0.245\ \mathrm{A}. If $$the force measured is $$0.0348\ \mathrm{N}$$ downward, what is the strength of the magnetic field $$B$$?

Accepted Answer

$$B = 1.42\ \mathrm{T}$$

Question 6

Which equation gives the force on a charge $$q$$ moving with velocity $$v at an $$angle $$	heta to a $$magnetic field $$B$$?

Accepted Answer

$$F = qvB\sin	heta$$

Question 7

A solenoid is $$0.5\ \mathrm{m}$$ long, has $$N = 1000$$ turns, and carries a current $$I = 2\ \mathrm{A}. $$What is the magnitude of the magnetic field inside the solenoid?

Accepted Answer

$$B = 8.0 	imes 10$$^{-3}$$\ \mathrm{T}$$

Question 8

Two parallel wires, each $$2\ \mathrm{m}$$ long and $$3\ \mathrm{mm}$$ apart, carry currents of $$8\ \mathrm{A} in $$opposite directions. What is the magnitude of the force between them?

Accepted Answer

$$F = 8.5 	imes 10$$^{-4}$$\ \mathrm{N}$$

Question 9

Which of the following best explains why the vertical sections of a rectangular current loop in a uniform magnetic field can be ignored when calculating the net force?

Accepted Answer

The forces on the vertical sections cancel each other out because they are equal and opposite.

Question 10

A circular loop of wire with $$N = 10$$ turns, diameter $$d = 0.10\ \mathrm{m}$$, and current $$I = 3\ \mathrm{A} is $$placed in a $$2\ \mathrm{T}$$ magnetic field. What is the maximum torque experienced by the loop?

Accepted Answer

$$	au_{max} = 0.24\ \mathrm{N\cdot m}$$

Question 11

Which device uses the torque on a current loop to measure electric current?

Accepted Answer

Galvanometer

Question 12

In a mass spectrometer, what is the speed $$v at $$which a charged particle will not be deflected by perpendicular electric and magnetic fields?

Accepted Answer

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

Question 13

Which of the following statements about ferromagnetic materials is correct?

Accepted Answer

Ferromagnetic materials can be strongly magnetized because their domains can be aligned by an external field.

Question 14

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

Accepted Answer

Tesla ($$\mathrm{T})$$

Question 15

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

Accepted Answer

Point your fingers in the direction of velocity, curl them toward the magnetic field; thumb points in the direction of force.

Question 16

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

Accepted Answer

Circle

Question 17

Which equation gives the magnetic field inside a long, tightly wound solenoid?

Accepted Answer

$$B = \dfrac{\mu_0$ N I}{\ell}$$

Question 18

Which statement about the force between two parallel wires is correct?

Accepted Answer

Parallel currents attract each other.

Question 19

What is the physical meaning of the magnetic dipole moment $$M$$ for a current loop?

Accepted Answer

It is the product of the current and the area of the loop.

Chapter 20: Magnetism – Study Notes

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