College Physics II Test 4

Which of the following statements are true?

The north pole of a magnet points towards Earth’s geographic north pole

An electron, moving west, enters a magnetic field. Because of this field the electron curves upward. We may conclude that the magnetic field must have a component      ?     .

Toward the north

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around each circle?

T

A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?

Horizontally toward the east

Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the magnetic force on the 20-A wire has magnitude F, what is the magnitude of the magnetic force on the 5-A wire? No external magnetic fields are present.

F

A long, straight, horizontal wire carries current toward the east. A proton moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the proton?

Toward the north

A proton moving with a velocity of 4.0 × 10⁴ m/s enters a magnetic field of 0.20 T. If the angle between the velocity of the proton and the direction of the magnetic field is 60°, what is the magnitude of the magnetic force on the proton? (e= 1.60 × 10^-19 C)

$$1.1 \times 10^{-15} N$$

A proton having a speed of 3.0 × 10⁶ m/s in a direction perpendicular to a uniform magnetic field moves in a circle of radius 0.20 m within the field. What is the magnitude of the magnetic field? (e = 1.60 × 10^-19 C, $<em>m_{</em>proton}$ = 1.67 × 10^-27 kg)

$$|q|vB = m v²/r$$

0.16 T

A straight wire carries a current of 10 A at an angle of 30° with respect to the direction of a uniform 0.30 T magnetic field. Find the magnitude of the magnetic force on a 0.50 m length of the wire.

0.75 N

Two long parallel wires that are 0.30 m apart carry currents of 5.0 A and 8.0 A in the opposite direction. Find the magnitude of the force per unit length that each wire exerts on the other wire and indicate if the force is attractive or repulsive. (μ₀ = 4π × 10^-7 T ∙ m/A)

$2.7 \times 10^{-5} N$ , repulsive

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions w = 0.60 m and L = 1.0 m, and carries a current I = 2.0 A in the direction shown. The magnetic field due to the magnet is uniform and of magnitude 0.80 T. The loop rotates in the magnetic field and at one point the plane of the loop is perpendicular to the field. At that instant, what is the magnitude of the torque (in N * m) acting on the wire due to the magnetic field?

0.00

At what distance from a long straight wire carrying a current of 5.0 A is the magnitude of the magnetic field due to the wire equal to the strength of Earth's magnetic field of about 5.0 × 10^-5 T? (μ₀ = 4π × 10^-7 T ∙ m/A)

$$B= \mu_0 I/2\pi r$$

2.0 cm

How many turns should a 10 cm long ideal solenoid have if it is to generate a 1.5 mT magnetic field when 1.0 A of current runs through it? (μ₀ = 4π × 10^-7 T ∙ m/A)

120

A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will      ?     .

Contain a north pole on the right and a south pole on the left

An electron moving along the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, then the magnetic field must have a component      ?     .

Along the - z-axis

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil?

Perpendicular to and into the page

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in the same direction,      ?     .

The wires pull toward each other

A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron?

Toward the south

A proton is projected with a velocity of 7.0 km/s into a magnetic field of 0.60 T perpendicular to the motion of the proton. What is the magnitude of the magnetic force that acts on the proton? (e = 1.60 × 10^-19 C)

$$6.7 \times 10^{-16} N$$

An electron moving perpendicular to a uniform magnetic field of 0.22 T moves in a circle with a speed of 1.5 × 10⁷ m/s. What is the radius of the circle? (e = 1.60 × 10^-19 C, m_e = 9.11 × 10^-31kg)

$$|q|vB=mv^{2}/r$$

0.39 mm

A straight 1.0 m long wire is carrying a current. The wire is placed perpendicular to a magnetic field of strength 0.20 T. If the wire experiences a force of 0.60 N, what is the current in the wire?

3.0 A

A flat circular loop carrying a current of 2.0 A is in a magnetic field of 3.5 T. The loop has an area of 0.12 m² and its plane is oriented at a 37° angle to the field. What is the magnitude of the magnetic torque (in N * m) on the loop?

0.67

The magnetic field at point P due to a 2.0 A current flowing in a long, straight, thin wire is 8.0 μT. How far is point P from the wire? (μ₀ = 4π × 10^-7 T ∙ m/A)

5.0 cm

How much current must pass through a 400 turn ideal solenoid that is 4.0 cm long to generate a 1.0 T magnetic field at the center? (μ₀ = 4π × 10^-7 T ∙ m/A)

80 A

If you were to cut a small permanent bar magnet in half      ?     .  

Each piece would in itself be a smaller bar magnet with both north and south poles

A proton, moving west, enters a magnetic field. Because of this magnetic field the proton curves upward. We may conclude that the magnetic field must have a component      ?     .

Toward the south

The direction of the force on a current-carrying wire in a magnetic field is _?_.

Perpendicular to both the current and magnetic field

Two long, parallel wires carry currents of different magnitudes. If the current in one of the wires is doubled and the current in the other wire is halved, what happens to the magnitude of the magnetic force that each wire exerts on the other?

It stays the same

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field ($\mu T$) at a distance of 1 cm from this wire?

2

An electron moves with a speed of 5.0 × 10⁴ m/s perpendicular to a uniform magnetic field of magnitude 0.20 T. What is the magnitude of the magnetic force on the electron? (e = 1.60 × 10^-19 C)

$$1.6 \times 10^{-15} N$$

An electron is accelerated from rest through a potential difference of 3.75 kV. It enters a region where a uniform 4.0 mT magnetic field is perpendicular to the velocity of the electron. Calculate the radius of the path this electron will follow in the magnetic field. (e = 1.60 × 10^-19 C, m_e = 9.11 × 10^-31 kg)

5.2 cm

What is the force per meter on a straight wire carrying 5.0 A when it is placed in a magnetic field of 0.020 T so that the wire makes an angle of 27° with respect to the magnetic field lines.

0.045 N/m

Two long parallel wires are 0.400 m apart and carry currents of 4.00 A and 6.00 A. What is the magnitude of the force per unit length (in $\mu N/m$) that each wire exerts on the other wire? (μ₀ = 4π × 10^-7 T ∙ m/A)

12.0

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions w = 0.60 m and L = 1.0 m, and carries a current I = 2.0 A in the direction shown. The magnetic field due to the magnet is uniform and of magnitude 0.80 T. The loop rotates in the magnetic field and at one point the plane of the loop makes a 30° angle with the field. At that instant, what is the magnitude of the torque (in N * m) acting on the wire due to the magnetic field?

0.48

Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the strength of the magnetic field midway between the two wires? (μ₀ = 4π × 10^-7 T ∙ m/A)

$$5.0 \times 10^{-5} T$$

An ideal solenoid is wound with 470 turns on a wooden form that is 4.0 cm in diameter and 50 cm long. The windings carry a current in the sense shown in the figure. The current produces a magnetic field of magnitude 4.1 mT, at the center of the solenoid. What is the current I in the solenoid windings? (μ0 = 4π × 10-7 T ∙ m/A)

3.5 A

A flat coil is in a uniform magnetic field. The magnetic flux through the coil is greatest when the plane of its area is      ?     .

Perpendicular to the magnetic field

A coil of wire containing N turns is in an external magnetic field that is perpendicular to the plane of the coil and it steadily changing. Under these circumstances, an emf ε is induced in the coil. If the rate of change of the magnetic field and the number of turns in the coil are now doubled (but nothing else changes), what will be the induced emf in the coil?

$$4\varepsilon$$

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 sense of the induced current in this coil as the field fades?

The induced current flows counterclockwise

As shown in the figure, one end of a metal bar is in contact with a circular rail and the other end is pivoted at P. A steady uniform, magnetic field B into the page is present. As the bar rotates about point P in a clockwise direction, the direction of the induced current through the resistor R is      ?     .

From b to a

A transformer is a device that normally ___.

Operates only on AC

An inductor stores energy in its magnetic field

True

A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a magnetic field with a strength of 0.40 T, as shown in the figure. The length of the loop L is 0.16 m and its width w is 0.040 m. What is the magnetic flux (T•m²) through the loop when the plane of the loop makes an angle of 60° with the magnetic field?

0.0022

The area of a rectangular loop of wire is 3.6 × 10-3 m². The loop is placed in a uniform magnetic field that changes steadily from 0.20 T to 1.4 T in 1.6 s. The plane of the loop is perpendicular to the direction of the magnetic field. What is the magnitude of the induced emf in that loop?

0.0027 V

A conducting rod of length ℓ= 25 cm is placed on a U-shaped metal wire that is connected to a lightbulb having a resistance of 8.0 Ω, as shown in the figure. The wire and the rod are in the plane of the page. A constant uniform magnetic field of strength 0.40 T is applied perpendicular to and into the paper. An applied external force pulls the rod to the right with a constant speed of 6.0 m/s. What is the magnitude of the emf induced in the rod?

0.6 V

The primary of an ideal transformer has 100 turns and its secondary has 200 turns. Neglecting frictional losses, if the power input to the primary is 100 W, we can expect the power output of the secondary to be      ?     .

100 W

The mutual inductance between two coils is 10 mH. The current in the first coil changes uniformly from 2.7 A to 5.0 A in 160 ms. If the second coil has a resistance of 0.60 Ω, what is the magnitude of the induced current in the second coil?

0.24 A

A coil with a self-inductance of 6.0 H is connected to a dc battery through a switch. As soon as the switch is closed, the rate of change of current is 2.0 A/s. What is the emf induced in this coil at this instant?

$$\varepsilon = L |\Delta i/ \Delta t|$$

12 V

A 4.0 mH coil carries a current of 5.0 A. How much energy is stored in its magnetic field?

None of these