Fechar
A charged particle is moving perpendicular to a magnetic field in a circle with a radius r.
An identical particle enters the field, with v perpendicular to B, but with a higher speed than the first particle. Compared with the radius of the circle for the first particle, is the radius of the circular path for the second particle
(a) smaller,
(b) larger, or
(c) equal in size?
A wire carries current in the plane of this screen toward the top of the screen. The wire experiences a magnetic force toward the right edge of the screen. Is the direction of the magnetic field causing this force
(a) in the plane of the screen and toward the left edge,
(b) in the plane of the screen and toward the bottom edge,
(c) out of the screen, or
(d) into the screen?
Four magnetic moments are shown in a uniform magnetic field. Which moments have the largest potential energy (= orientation energy)?
(a) 1 and 2
(b) 2 and 3
(c) 3 and 4
(d) 1 and 4
(e) All tie
Consider a solenoid that is very long compared with its radius. Of the following choices, what is the most effective way to increase the magnetic field in the interior of the solenoid?
(a) double its length, keeping the number of turns per unit length constant
(b) reduce its radius by half, keeping the number of turns per unit length constant
(c) overwrap the entire solenoid with an additional layer of current-carrying wire
The figure shows four arrangements in which long parallel wires carry equal currents directly into or out of the page at the corners of identical squares. Rank the arrangements according to the magnitude of the net magnetic field at the center of the square, greatest first.
(a) Ba > Bc > Bd > Bb
(b) Bc > Bd > Ba = Bb
(c) Ba = Bb > Bc > Bd
(d) Ba = Bb > Bd > Bc
The figure shows four identical currents 𝑖 and five Amperian loops (𝑎 through 𝑒) encircling them. Rank the paths according to the
value of ∮ 𝐵 ' 𝑑𝑠⃗ taken in the direction shown, most positive first.
a) d > a = e > b > c
b) a = e > b > c > d
c) d > e > a = b > c
d) a = b = c = d = e
e) a > b > c > d > e
The figure shows three circuits consisting of straight radial lengths and concentric circular arcs (either half- or quarter-circles of radii 𝑟, 2𝑟, and 3𝑟). The circuits carry the same current. Rank them according to the magnitude of the magnetic field produced at the center of curvature (the dot), greatest first:
a) a>b>c
b) c>b>a
c) b=a>c
d) c>a=b
e) a>c>b
A spatially uniform magnetic field cannot exert a magnetic force on a particle in which of the following circumstances? There may be more than one correct statement.
a) The particle is charged.
b) The particle moves perpendicular to the magnetic field.
c) The particle moves parallel to the magnetic field.
d) The magnitude of the magnetic field changes with time.
e) The particle is at rest.
A proton moving horizontally enters a region where a uniform magnetic field is directed perpendicular to the proton’s velocity as shown in the figure. After the proton enters the field, it
a) is deflected downward, with its speed remaining constant.
b) is deflected upward, moving in a semicircular path with constant speed, and exits the field moving to the left.
c) continues to move in the horizontal direction with constant velocity.
d) moves in a circular orbit and become trapped by the field.
At a certain instant, a proton is moving in the positive x direction through a magnetic field in the negative z direction. What is the direction of the magnetic force exerted on the proton?
a) positive z direction
b) negative z direction
c) positive y direction
d) negative y direction
e) The force is zero.
A thin copper rod 1.00 m long has a mass of 50.0 g. What is the minimum current in the rod that would allow it to levitate above the ground in a magnetic field of magnitude 0.100 T?
a) 1.20 A
b) 2.40 A
c) 4.90 A
d) 9.80 A
e) none of these
Classify the following statement as a characteristic: of electric forces only,
of magnetic forces only,
of both electric and magnetic forces, or of neither electric nor magnetic forces.
The force is proportional to the magnitude of the field exerting it.
a) electric forces
b) magnetic forces
c) both electric and magnetic forces
d) neither electric nor magnetic forces
Classify the following statement as a characteristic: of electric forces only,
of magnetic forces only,
of both electric and magnetic forces, or of neither electric nor magnetic forces.
The force exerted on a moving charged object is zero.
a) electric forces
b) magnetic forces
c) both electric and magnetic forces
d) neither electric nor magnetic forces
Consider the situation shown. A triangular, aluminum loop is slowly moving to the right. Eventually, it will enter and pass through the uniform magnetic field region represented by the tails of arrows directed away from you. Initially, there is no current in the loop. When the loop is entering the magnetic field, what will be the direction of any induced current present in the loop?
a) clockwise
b) counterclockwise
c) No current is induced
A rigid, circular metal loop begins at rest in a uniform magnetic field directed away from you as shown. The loop is then pulled through the field toward the right, but does not exit the field. What is the direction of any induced current within the loop?
a) clockwise
b) counterclockwise
c) No current is induced
The figure shows a circular loop of wire falling toward a wire carrying a current to the left. What is the direction of the induced current in the loop of wire?
a) clockwise
b) counterclockwise
c) zero
d) impossible to determine
In an AC generator, a coil with N turns of wire spins in a magnetic field. Of the following choices, which does not cause an increase in the emf generated in the coil?
a) replacing the coil wire with one of lower resistance
b) spinning the coil faster
c) increasing the magnetic field
d) increasing the number of turns of wire on the coil
A flat coil of wire is placed in a uniform magnetic field that is in the y direction. The magnetic flux through the coil is a zero if the plane of the coil is: (More than one answer may be correct.)
a) in the xy plane
b) in the yz plane
c) in the xz plane
d) in any orientation, because it is a constant
A circular loop of wire with a radius of 4.0 cm is in a uniform magnetic field of magnitude 0.060 T. The plane of the loop is perpendicular to the direction of the magnetic field. In a time interval of 0.50 s, the magnetic field changes to the opposite direction with a magnitude of 0.040 T. What is the magnitude of the average emf induced in the loop?
a) 0.20 V
b) 0.025 V
c) 5.0 mV
d) 1.0 mV
e) 0.2 mV
The bar in the figure moves on rails to the right with a velocity v, and a uniform, constant magnetic field is directed out of the page. Which of the following statements are correct? More than one statement may be correct.
a) The induced current in the loop is zero.
b) The induced current in the loop is clockwise.
c) The induced current in the loop is
counterclockwise.
d) An external force is required to keep the bar moving at constant speed.
e) No force is required to keep the bar
moving at constant speed.
Two coils are placed near each other as shown in the figure. The coil on the left is connected to a battery and a switch, and the coil on the right is connected to a resistor. What is the direction of the current in the resistor at an instant immediately after the switch is thrown closed?
a) left
b) right
c) the current is zero
Consider the circuit in the figure with S1 open and S2 at position a. Switch S1 is now thrown closed. At the instant it is closed, across which circuit element is the voltage equal to the emf of the battery?
a) the resistor
b) the inductor
both the inductor and resistor
Consider the circuit below. Switch S is closed at t = 0. What is the current through the inductor L just after the switch is closed?
a) 0
b) 1 A
C) 2 A
d) 3 A
Consider the circuit below. Switch S is closed at t = 0. What is the voltage across inductor L just after the switch is closed?
a) 0
b) 1
c) 6
d) 3
Consider the circuit below. Switch S is closed at t = 0. What is the voltage across the inductor L just after the switch is closed?
a) 0 A
b) 1 A
c) 2 A
d) 4 A
Consider the following circuits. Two identical batteries are connected to two identical inductors as shown. The switches are closed for a very long time. At t = 0, both switches are opened. Which resistor dissipates more total energy after the switches are opened?
a) The 1-Ω resistor in A dissipates more energy.
b) The 2-Ω resistor in B dissipates more energy.
c) Both resistors dissipate the same amount of energy.
d) The amounts of energy dissipated cannot be compared.
A lab tech observes that the current in a coil of conducting wire goes from i1 = 0.200 A to i2 = 1.50 A in a time interval of Δt = 0.150 s.
Assuming the coil's inductance is L = 2.00 mH, what is the magnitude of the average induced emf (in mV) in the coil for this time interval?
a) 21 mV
b) 17.3 mV
c) 19.6 mV
d) 15.5 mV
Consider the RL circuit shown in the figure, where R = 14.3 Ω. The switch S is closed at t = 0. At t = 3.00 ms, the current has reached 88.3% of its final value. What is the inductance (in mH)?
a) 20 mH
b) 22.8 mH
c) 19.6 mH
d) 19.2 mH
An LC circuit oscillates at a frequency of 130 Hz. If the capacitance is
4.73 µF, what is the inductance (in H)?
a) 0.57 H
b) 0.37 H
c) 0.87 mV
d) 0.67 mV
What is the impedance of a series RLC circuit at resonance?
a) larger than R
b) less than R
c) equal to R
d) impossible to determine
A series RLC circuit has R = 425 , L = 1.25 H, and C = 3.5
F. If this circuit is driven by a 60-Hz source with Vmax = 150 V, what is the impedance of the circuit?
a) 408 𝛺
b) 488 𝛺
c) 513 𝛺
d) 550 𝛺
An 8.00- F capacitor is connected to the terminals of a 60.0-Hz AC source whose rms voltage is 150 V. Find the capacitive reactance and the rms current in the circuit.
a) 0.542 A
b) 0.245 A
c) 0.225 A
d) 0.452 A
In a purely inductive AC circuit, L = 25.0 mH and the rms voltage is 150 V. What is the inductive reactance and rms current in the circuit if the frequency is 60.0 Hz.
a) 15.9 A
b) 14.9 A
c) 16.9 A
d) 13.9 A
Consider the AC circuit in the figure. The frequency of the AC source is adjusted while its voltage amplitude is held constant. When does the lightbulb glow the brightest?
a) It glows brightest at high frequencies.
b) It glows brightest at low frequencies.
c) The brightness is the same
at all frequencies.
The voltage output of an AC source is given by the expression �v = 200 sin t, where �v is in volts. Find the rms current in the circuit when this source is connected to a 47.0- resistor.
a) 4.25 A
b) 3.01 A
c) 2.06 A
d) 3.50 A
Consider the voltage phasor in the figures, shown at three instants of time. Choose the part of the figure, (a), (b), or (c), that represents the instant of time at which the instantaneous value of the voltage has the largest magnitude.
A charged capacitor and an inductor are connected in series at time 𝑡 = 0. In terms of the period 𝑇 of the resulting oscillations, determine how much later the following reach again for the first time their maximum value: the charge on the capacitor
a) 𝑇/4
b) 𝑇/2
c) 𝑇
d) 2𝑇
e) 4𝑇
The current in an oscillating LC circuit is zero. Which one of the following
statements is true?
a) The charge on the capacitor is equal to zero coulombs.
b) Charge is moving through the inductor.
c) The energy is equally shared between the electric and magnetic fields.
d) The energy in the electric field is maximized.
e) The energy in the magnetic field is maximized.
