PHYS 2426 Exam 2 Review

Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire. If the length of the solenoid became twice as long (2L), and all other quantities remained the same, the magnetic field inside the solenoid would

become one half as strong

The three loops of wire shown in the figure are all subject to the same uniform magnetic field B that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an emf induced in them?

loop 2 only

The long straight wire in the figure carries a current I that is decreasing with time at a constant rate. The circular loops A, B, and C all lie in a plane containing the wire. The induced emf in each of the loops A, B, and C is such that

loop A has a counter-clockwise emf, loop B has no induced emf, and loop C has a clockwise emf

In the figure, the current in a solenoid having no appreciable resistance is flowing from b to a and is decreasing at a rate of 2.8 A/s. The self-induced emf in the solenoid is found to be 8.9 V. Which point, a or b is at higher potential?

point a

Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire. If the radius of the solenoid were doubled (becoming 2b), and all other quantities remained the same, the magnetic field inside the solenoid would

remain the same

A charge is accelerated from rest through a potential difference V and then enters a uniform magnetic field oriented perpendicular to its path. The field deflects the particle into a circular arc of radius R. If the accelerating potential is tripled to 3V, what will be the radius of the circular arc?

sqrt(3)R

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field at a point directly below the wire points

to the right

An electron, moving toward the west, enters a uniform magnetic field. Because of this field the electron curves upward. The direction of the magnetic field is

towards the north

A vertical wire carries a current straight down. To the east of this wire, the magnetic field points

towards the south

A 5.0-ohm resistor and a 9.0-ohm resistor are connected in parallel. A 4.0-ohm resistor is then connected in series with this parallel combination. An ideal 6.0-V battery is then connected across the series-parallel combination of the three resistors. What is the current through (a) the 4.0-ohm resistor? (b) the 5.0-ohm resistor? (c) the 9.0-ohm resistor?

(a) 0.83 A (b) 0.53 A (c) 0.30 A

As shown in the figure, a rectangular current loop is carrying current I_1 = 3.0 A, in the direction shown, and is located near a long wire carrying a current I_w. The long wire is parallel to the sides of the rectangle. The rectangle loop has length 0.80 m and its sides are 0.10 m and 0.70 m from the wire, as shown. We measure that the net force on the rectangular loop is 4.9 × 10^-6 N and is directed towards the wire.(µ0 = 4pi × 10^-7 T • m/A) (a) What is the magnitude of the current I_w? (b) In which direction does I_w flow: from top to bottom or from bottom to top in the sketch?

(a) 1.2 A (b) from bottom to top

5) For the circuit shown in the figure, determine the current in (a) the 7.0-ohm resistor. (b) the 8.0-ohm resistor. (c) the 4.0-ohm resistor

(a) 1.6 A (b) 1.3 A (c) 0.28 A

An electron moves with a speed of 8.0 × 10^6 m/s along the +x-axis. It enters a region where there is a magnetic field of 2.5 T, directed at an angle of 60° to the +x-axis and lying in the xy-plane. (1 eV = 1.60 × 10^-19 C, m_el = 9.11 × 10^-31 kg) Calculate the magnitude of (a) the magnetic force on the electron. (b) the acceleration of the electron.

(a) 2.8 × 10-12 N (b) 3.0 × 1018 m/s^2

Three resistors are connected across an ideal 2.0-V DC battery as shown in the figure. (a) At what rate does the battery supply energy to the resistors? (b) At what rate is heat produced in the 6.0-ohm resistor?

(a) 3.0 W (b) 0.67 W

A 200-loop coil of cross sectional area 8.5 cm^2 lies in the plane of the page. An external magnetic field of 0.060 T is directed out of the plane of the page. The external field decreases to 0.020 T in 12 milliseconds. (a) What is the magnitude of the change in the external magnetic flux enclosed by the coil? (b) What is the magnitude of the average voltage induced in the coil as the external flux is changing? (c) If the coil has a resistance of 4.0 ohms, what is the magnitude of the average current in the coil?

(a) 4.0 × 10^-3 T • m^2 (b) 0.57 V (c) 0.14

The mutual inductance between two coils is 10.0 mH. The current in the first coil changes uniformly from 2.70 A to 5.00 A in 0.160 s. If the second coil has a resistance of 0.600 ohms, what is the magnitude of the induced current in the second coil?

0.240 A

In the figure, the current in a solenoid having no appreciable resistance is flowing from b to a and is decreasing at a rate of 9.8 A/s. The self-induced emf in the solenoid is found to be 2.6 V. What is the self-inductance of the solenoid?

0.27 H

The length of a conducting rod moving in a uniform magnetic field B =0.60 T is 0.10 m. Its velocity is 2.5 m/s, Resistance of the loop is 0.030 Ohm. Find the force acting on the rod

0.30 N

A straight wire that is 0.60 m long is carrying a current of 2.0 A. It is placed in a uniform magnetic field of strength 0.30 T. If the wire experiences a force of 0.18 N, what angle does the wire make with respect to the magnetic field?

30 degrees

When four identical resistors are connected to an ideal battery of voltage V = 10 V as shown in the figure, the current I is equal to 0.20 A. What is the value of the resistance R of the resistors?

30 ohms

A galvanometer G has an internal resistance rg. An AMMETER is constructed by incorporating the galvanometer and an additional resistance Rs. Which one of the figures below is the most appropriate circuit diagram for the ammeter?

4 (option 4: G, rg, and Rs are all in series together in a rectangle shape)

Which of the following statements about inductors are correct? There may be more than one correct choice

An inductor always resists any change in the current through it

A circular loop of radius 0.10 m is rotating in a uniform external magnetic field of 0.20 T. Find the magnetic flux through the loop due to the external field when the plane of the loop and the magnetic field vector are (a) parallel. (b) perpendicular. (c) at an angle of 30° with each other.

(a) zero (b) 6.3 × 10^-3 T • m^2 (c) 3.1 × 10^-3 T • m^2

A point charge Q moves on the x-axis in the positive direction with a speed of 280 m/s. A point P is on the y-axis at y = +70 mm. The magnetic field produced at the point P, as the charge moves through the origin, is equal to -0.30 μT k. What is the charge Q? (μ0 = 4pi × 10^-7 T • m/A)

-53 μC

An electron moving in the direction of the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, the direction of the magnetic field in this region points in the direction of the

-z axis

A charged particle of mass 0.0020 kg is subjected to a 6.0 T magnetic field which acts at a right angle to its motion. If the particle moves in a circle of radius 0.20 m at a speed of 5.0 m/s, what is the magnitude of the charge on the particle?

0.0083 C

A charged particle of mass 0.0040 kg is subjected to a 6.0 T magnetic field which acts at a right angle to its motion. If the particle moves in a circle of radius 0.20 m at a speed of 4.0 m/s, what is the magnitude of the charge on the particle?

0.013 C

A 15.00 cm long solenoid with radius 3.50 cm is closely wound with 750 turns of wire. The current in the windings is 8.00 A. What is the magnetic field near the center of the solenoid?

0.0502 T

At a certain instant the current flowing through a 5.0 H inductor is 3.0 A. If the energy in the inductor at this instant is increasing at a rate of 3.0 J/s, how fast is the current changing?

0.20 A/s

At a certain instant the current flowing through a 5.0-H inductor is 3.0 A. If the energy in the inductor at this instant is increasing at a rate of 3.0 J/s, how fast is the current changing?

0.20 A/s

A point charge Q moves on the x-axis in the positive direction with a speed of 370 m/s. A point P is on the y-axis at y = +80 mm. The magnetic field produced at point P, as the charge moves through the origin, is equal to -0.80 μT k. When the charge is at x = +40 mm, what is the magnitude of the magnetic field at point P? (μ0 = 4pi × 10^-7 T • m/A)

0.57 μT

Three resistors having resistances of 4.0 ohms, 6.0 ohms, and 10.0 ohms are connected in parallel. If the combination is connected in series with an ideal 12-V battery and a 2.0-ohm resistor, what is the current through the 10.0-ohm resistor?

0.59 A

Four resistors are connected across an 8-V DC battery as shown in the figure. The current through the 9-ohm resistor is closest to

0.7 A

An LC circuit consists of a 3.4-µF capacitor and a coil with a self-inductance 0.080 H and no appreciable resistance. At t = 0 the capacitor has a charge of 5.4 µC and the current in the inductor is zero. How long after t = 0 will the current in the circuit be maximum?

0.82 ms

Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. The electric charge of each of the three particles is, respectively

1 is negative, 2 is neutral, and 3 is positive

At what rate would the current in a 100 - mH inductor have to change to induce an emf of 1000 V in the inductor?

10,000 A/s

At what rate would the current in a 100-mH inductor have to change to induce an emf of 1000 V in the inductor?

10,000 A/s

When a potential difference of 10 V is placed across a certain solid cylindrical resistor, the current through it is 2 A. If the diameter of this resistor is now tripled, the current will be

18 A

What resistance should be added in series with a 7.0-H inductor to complete an LR circuit with a time constant of 3.0 ms?

2.3 k Ohm

An electron traveling toward the north with speed 4.0 × 10^5 m/s enters a region where the Earth's magnetic field has the magnitude 5.0 × 10^-5 T and is directed downward at 45° below horizontal. What is the magnitude of the force that the Earth's magnetic field exerts on the electron? (e = 1.60 × 10^-19 C)

2.3 x 10^-18 N

For the circuit shown in the figure, I = 0.50 A and R = 12 ohm. What is the value of the emf E?

24 V (figure shows battery connected in series with R and 2R with another 2R in parallel with the battery connected at the node between R and 2R)

How much energy is stored in a room 3.0 m by 4.0 by 2.4. m due to the earth's magnetic field with a strength of 5.0 ×10^-5 T

29 mJ

For the circuit shown in the figure, all quantities are accurate to 3 significant figures. What is the power dissipated in the 2-ohm resistor?

3.56 W

An inductor has a current I(t) = (0.500 A) cos[(275 s -1)t] flowing through it. If the maximum emf across the inductor is equal to 0.500 V, what is the self-inductance of the inductor?

3.64 mH

A circular loop of wire of radius 10 cm carries current of 6.0 A. What is the magnitude of the magnetic field at the center of the loop?

3.80 × 10^-5

What is the self-inductance of a solenoid 30.0 cm long having 100 turns of wire and a cross-sectional area of 1.00 × 10^-4 m^2? (μ0 = 4pi × 10^-7 T • m/A)

4.19 µH

What is the self-inductance of a solenoid 30.0 cm long having 100 turns of wire and a cross-sectional area of 1.00 × 10-4 m2? (μ0 = 4pi × 10^-7 T • m/A)

4.19 μH

A wire along the z - axis carries a current of 1.7 A in the positive z - direction. Find the force exerted on a 9.3-cm long length of the wire by a uniform magnetic field with magnitude 0.27 T in the - x direction.

4.2687 × 10^-2 Negative y direction

A thin copper rod that is 1.0 m long and has a mass of 0.050 kg is in a magnetic field of 0.10 T. What minimum current in the rod is needed in order for the magnetic force to cancel the weight of the rod?

4.9 A

Two unknown resistors are connected together. When they are connected in series their equivalent resistance is 15 ohm. When they are connected in parallel, their equivalent resistance is 3.3 ohm. What are the resistances of these resistors?

4.9 ohm and 10 ohm

A resistor is made out of a long wire having a length L. Each end of the wire is attached to a terminal of a battery providing a constant voltage V0. A current I flows through the wire. If the wire were cut in half, making two wires of length L/2, and both wires were attached to the battery (the end of both wires attached to one terminal, and the other ends attached to the other terminal), what would be the total current flowing through the two wires?

4I

What is the maximum current that can be drawn from a 1.50-V battery with an internal resistance of 0.30 ohm?

5.0 A

A 4.0-mF capacitor is discharged through a 4.0-kilo ohm resistor. How long will it take for the capacitor to lose half its initial stored energy?

5.5 s

An electric field of 1800 V/m and a magnetic field of 0.50 T act on a moving charge and produce no force. Calculate the minimum speed of the electron

6.0 ohms

A 96-mH solenoid inductor is wound on a form 0.80 m in length and 0.10 m in diameter. A coil is tightly wound around the solenoid at its center. The coil's resistance is 9.9 ohms. The mutual inductance of the coil and solenoid is 31 μH. At a given instant, the current in the solenoid is 540 mA, and is decreasing at the rate of 2.5 A/s. At the given instant, what is the magnitude of the induced current in the coil? (μ0 = 4pi × 10^-7 T • m/A)

7.8 μA

As shown in the figure, a wire and a 10-ohm resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm. A uniform but non-steady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is decreased from 1.50 T to 0.50 T in a time interval of 51 ms. The average induced current and its direction through the resistor, in this time interval, are closest to

78 mA, from b to a

The magnetic field at a distance of 2 cm from a current carrying wire is 4 µT. What is the magnetic field at a distance of 4 cm from the wire?

8 µT

Thirteen resistors are connected across points A and B as shown in the figure. If all the resistors are accurate to 2 significant figures, what is the equivalent resistance between points A and B?

8.0 ohms

A proton is first accelerated from rest through a potential difference V and then enters a uniform 0.750-T magnetic field oriented perpendicular to its path. In this field, the proton follows a circular arc having a radius of curvature of 1.84 cm. What was the potential difference V? (m_proton = 1.67 × 10^-27 kg, e = 1.60 × 10^-19 C)

9.12 kV

An electron experiences a magnetic force of 4.6×10^-15 N when moving at an angle of 60 degrees with respect to a magnetic field of 3.5×10^-3 T. Find the speed of the electron.

9.48×10^6 m/s

In the circuit shown in the figure, all the lightbulbs are identical. Which of the following is the correct ranking of the brightness of the bulbs?

A is the brightest, and B and C have equal brightness but less than A

A large magnetic flux change through a coil must induce a greater emf in the coil than a small flux change.

False

An RC circuit is connected across an ideal DC voltage source through an open switch. The switch is closed at time t = 0 s. Which of the following statements regarding the circuit are correct? (There may be more than one correct choice.)

Once the capacitor is essentially fully charged, there is no appreciable current in the circuit.

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/sqrt(2)

The figure shows three identical lightbulbs connected to a battery having a constant voltage across its terminals. What happens to the brightness of lightbulb 1 when the switch S is closed?

The brightness increases permanently

Two light bulbs, B1 and B2, are connected to a battery having appreciable internal resistance as shown in the figure. What happens to the brightness of bulb B1 when we close the switch S?

The brightness of B1 decreases permanently

A light bulb is connected in the circuit shown in the figure with the switch S open. All the connecting leads have no appreciable resistance and the battery has no internal resistance. When we close the switch, which statements below accurately describe the behavior of the circuit? (There may be more than one correct choice.)

The brightness of the bulb will increase and the potential drop across R2 will decrease

Two very long parallel wires are a distance d apart and carry equal currents in opposite directions. The locations where the net magnetic field due to these currents is equal to zero are

The net field is not zero anywhere

The figure shows a bar magnet moving vertically upward toward a horizontal coil. The poles of the bar magnets are labeled X and Y. As the bar magnet approaches the coil it induces an electric current in the direction indicated on the figure (counter-clockwise as viewed from above). What are the correct polarities of the magnet?

X is a south pole, Y is a north pole

In the circuit shown in the figure, four identical resistors labeled A to D are connected to a battery as shown. S1 and S2 are switches. Which of the following actions would result in the GREATEST amount of current through resistor A?

closing both switches

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the direction of the induced current in this coil as the field fades?

counter-clockwise

A resistor and a capacitor are connected in series across an ideal battery having a constant voltage across its terminals. At the moment contact is made with the battery the voltage across the resistor is

equal to the battery's terminal voltage

A charged particle is moving with speed v perpendicular to a uniform magnetic field. A second identical charged particle is moving with speed 2v perpendicular to the same magnetic field. If the frequency of revolution of the first particle is f, the frequency of revolution of the second particle is

f

In the figure, a bar magnet moves away from the solenoid. The induced current through the resistor R is

from a to b

As more resistors are added in parallel across a constant voltage source, the power supplied by the source

increases

A resistor and a capacitor are connected in series across an ideal battery having a constant voltage across its terminals. At the moment contact is made with the battery the voltage across the capacitor is

zero