Q: A circuit consists of a battery, a resistor, and a capacitor as shown. If the battery is 9.0 V, the resistor is 1.5 kΩ, and the capacitor is 2.0 μF, what is the time constant of the circuit?

$$\tau = RC = (1.5 \times 10^3$) \times (2.0 \times 10$$^{-6}$$) = 3.0 \times 10$$^{-3}$$ \ \text{s}$$

Q: A 12 V battery is connected to a series circuit with a 4 Ω and a 2 Ω resistor. What is the current in the circuit?

$$I = \frac{12}{4+2} = 2 \ \text{A}$$

Q: Which of the following best describes the force on a current-carrying wire in a magnetic field?

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

Q: A 5.0 m long wire carries a current of 2.0 A perpendicular to a magnetic field of 0.30 T. What is the magnitude of the force on the wire?

$$F = I L B = 2.0 \times 5.0 \times 0.30 = 3.0 \ \text{N}$$

Question 1

A circuit consists of a battery, a resistor, and a capacitor as shown. If the battery is 9.0 V, the resistor is 1.5 kΩ, and the capacitor is 2.0 μF, what is the time constant of the circuit?

Accepted Answer

$$	au = RC = (1.5 	imes 10^3$) 	imes (2.0 	imes 10$$^{-6}$$) = 3.0 	imes 10$$^{-3}$$ \ 	ext{s}$$

Question 2

Two long, straight wires are placed parallel to one another 9 cm apart. Wire 1 carries a current of 4.0 A out of the page, and wire 2 carries a current of 8.0 A into the page. What is the direction of the magnetic field at a point 6 cm to the right of wire 1?

Accepted Answer

Out of the page

Question 3

A rectangular loop of wire is placed in a uniform magnetic field pointing into the page. If the loop is rotated 90 degrees about an axis in its plane, what happens to the magnetic flux through the loop?

Accepted Answer

The flux becomes zero.

Question 4

A proton is moving with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$What is the radius of the circular path it follows?

Accepted Answer

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

Question 5

Which of the following statements about the magnetic field inside a solenoid is correct?

Accepted Answer

The magnetic field is uniform and parallel to the axis of the solenoid.

Question 6

A 10 Ω, 20 Ω, and 30 Ω resistor are connected in parallel. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = \left( \frac{1}{10} + \frac{1}{20} + \frac{1}{30} \$$right)^{-1}$$ = 5.45 \ \Omega$$

Question 7

A rectangular loop of wire is moving at constant velocity into a region of uniform magnetic field directed into the page. What is the direction of the induced current in the loop?

Accepted Answer

Clockwise

Question 8

A charged particle enters a region with a uniform magnetic field perpendicular to its velocity. Which of the following best describes its motion?

Accepted Answer

It moves in a circular path.

Question 9

If the current in a long straight wire is doubled, what happens to the magnetic field at a fixed distance from the wire?

Accepted Answer

It doubles.

Question 10

A loop of wire with area $$A is $$placed in a magnetic field $$B at an $$angle $$	heta to $$the field. What is the expression for the magnetic flux through the loop?

Accepted Answer

$$\Phi = B A \cos 	heta$$

Question 11

A rectangular wire loop is pulled at constant speed from a region with no magnetic field into a region with a uniform magnetic field. What is the direction of the induced current as the loop enters the field?

Accepted Answer

It is clockwise as viewed from above.

Question 12

A 12 V battery is connected to a series circuit with a 4 Ω and a 2 Ω resistor. What is the current in the circuit?

Accepted Answer

$$I = \frac{12}{4+2} = 2 \ 	ext{A}$$

Question 13

Which of the following best describes the force on a current-carrying wire in a magnetic field?

Accepted Answer

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

Question 14

A 5.0 m long wire carries a current of 2.0 A perpendicular to a magnetic field of 0.30 T. What is the magnitude of the force on the wire?

Accepted Answer

$$F = I L B = 2.0 	imes 5.0 	imes 0.30 = 3.0 \ 	ext{N}$$

Question 15

A bar magnet is dropped through a coil of wire. As it falls, what is observed in the coil?

Accepted Answer

An induced current is observed, first in one direction, then in the opposite.

PHYS 202 Exam III Study Guidance: Magnetic Fields, Circuits, and Forces

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