Question 1

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current
A) points directly away from you.
B) points to the left.
C) circles the wire in a clockwise direction.
D) circles the wire in a counter-clockwise direction.

Accepted Answer

The answer of A horizontal wire carries a current straight...

Question 2

A long straight wire carrying a 4-A current is placed along the x-axis as shown in the figure. What is the direction of the magnetic field at a point P due to this wire? 
A) into the plane of the page
B) out of the plane of the page
C) along the -x-axis
D) along the +x-axis
E) along the +y-axis

Accepted Answer

The answer of A long straight wire carrying a 4-A...

Question 3

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop inside the loop, the magnetic field lines caused by this current
A) circle the loop in a clockwise direction.
B) circle the loop in a counterclockwise direction.
C) point straight up.
D) point straight down.

Accepted Answer

According to the right-hand rule for magnetic fields, the magnetic field lines created by a current-carrying loop of wire will point out of the plane of the loop inside the loop itself. Therefore, the correct answer is that the field lines point straight up (choice C).

Question 4

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 1 cm from this wire?
A) 2 μT
B) 4 μT
C) 6 μT
D) 8 μT
E) 10 μT

Accepted Answer

The magnetic field (B) around a long straight conductor is given by B = μ₀I/(2πr), where μ₀ is the permeability of free space, I is the current, and r is the distance from the wire. This formula shows that the magnetic field is inversely proportional to the distance from the wire. Therefore, if the distance is halved, the magnetic field will double. Since the magnetic field at 2 cm is 4 μT, at 1 cm, it will be 8 μT.

Question 5

An electron traveling toward the magnetic north with speed 400 km/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 magnitude magnetic force acts on the electron? (e = 1.60 × 10^-19C)

Accepted Answer

The answer of An electron traveling toward the magnetic north...

Question 6

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^-19C) A) 4.4 × 10^-14 N B) 1.6 × 10^-15 N C) 5 × 10^-20 N D) 2.6 × 10^-24 N E) zero

Accepted Answer

The magnetic force on a moving charge is given by the equation F = qvBsinθ, where q is the charge, v is the velocity, B is the magnetic field magnitude, and θ is the angle between v and B. In this case, the electron is moving perpendicular to the magnetic field (θ = 90°), so sinθ = 1. Plugging in the given values with the charge of an electron (q = -1.6 × 10^-19 C), we get F = (-1.6 × 10^-19 C)(5.0 × 10^14 m/s)(0.20 T)(1) = -1.6 × 10^-15 N. However, since the electron is negatively charged, the direction of the force is opposite to the direction of motion, so we take the magnitude to be positive. Therefore, the magnitude of the magnetic force on the electron is 1.6 × 10^-15 N, which is closest to choice B, 1.6 × 10^-15 N.

Question 7

A geophysicist measures the magnetic force on a proton that is moving vertically downward at a point 1.996 km/s at the earth's equator. At that location, the earth's magnetic magnetic field is horizontal and has a strength of 0.40 × 10^-4 T. What are the magnitude and direction of the force she will measure? (e = 1.60 × 10^-19C)

Accepted Answer

The answer of A geophysicist measures the magnetic force on...

Question 8

Which one of the following statements is correct?
A) When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point opposite to the direction of the magnetic field lines.
B) When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point in the direction of the magnetic field lines.
C) When a current-carrying wire is in your left hand, with your thumb in the direction of the current, your fingers point in the direction of the magnetic field lines.

Accepted Answer

This is known as the right-hand rule for magnetic fields. If you imagine grasping the wire with your right hand and having your thumb point in the direction of the current flow, then your fingers will naturally curl in the direction of the magnetic field lines around the wire.

Question 9

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of
A) 16d.
B) 8d.
C) 4d.
D) 2d.
E) d $\sqrt { 2 }$

Accepted Answer

The magnetic field produced by a long straight wire is proportional to the inverse of the distance from the wire. Therefore, if the field is reduced by a factor of 4 (from 20 mT to 5 mT), the distance from the wire must be multiplied by a factor of 4 in order to maintain the same proportionality. Therefore, the distance from the wire must be 4d.

Question 10

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes
A) smaller.
B) zero.
C) larger.

Accepted Answer

When a ferromagnetic material is placed in an external magnetic field, the magnetic domains align themselves with the external field, causing the net magnetic field of the material to become larger. This results in an increase in the overall magnetic moment of the material, making it more strongly magnetic.

Question 11

When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length and current) fixed, the magnetic field at the center of the solenoid will
A) double.
B) triple.
C) quadruple.
D) be reduced by a factor of one-half.
E) be reduced by a factor of one-fourth.

Accepted Answer

According to the formula for the magnetic field inside an ideal solenoid,

B = μ₀ * n * I

where B is the magnetic field, μ₀ is the permeability of free space, n is the number of turns per unit length (also known as the "turns density"), and I is the current.

If we double the number of windings while keeping all other parameters fixed, then n will double as well. This means that the magnetic field B will also double, since it is directly proportional to n. Therefore, the correct answer is A) double.

Question 12

A single current-carrying circular loop of radius R is placed next to a long, straight wire, as shown in the figure. The current I in the wire flows to the right. In which direction must current flow in the loop to produce a net magnetic field of zero at its center? 
A) counterclockwise
B) clockwise
C) It could be either clockwise or counterclockwise.
D) The current in the loop should be zero.

Accepted Answer

According to the Right Hand Rule, the magnetic field produced by the current in the wire at the center of the loop points out of the page, perpendicular to the plane of the loop. To cancel out this magnetic field, the current in the loop must produce a magnetic field pointing into the page. This can be achieved by using the Right Hand Rule again and determining that current must flow clockwise in the loop. Therefore, the correct answer is B) clockwise.

Question 13

A proton moving at 5.0 × 10⁴ m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10^-19C)

Accepted Answer

The answer of A proton moving at 5.0 × 10⁴...

Question 14

A vertical wire carries a current vertically downward. To the east of this wire, the magnetic field points
A) north.
B) east.
C) south.
D) down.

Accepted Answer

According to the right-hand rule for magnetic fields, if your right-hand thumb points in the direction of the current, then your fingers will wrap around the wire in the direction of the magnetic field. Therefore, to the east of the wire, the magnetic field will point south.

Question 15

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the radius of the solenoid is doubled to 2b, but all the other quantities remain the same, the magnetic field inside the solenoid will
A) remain the same.
B) become twice as strong as initially.
C) become one-half as strong as initially.
D) become four times as strong as initially.
E) become one-fourth as strong as initially.

Accepted Answer

The magnetic field inside an ideal solenoid is given by $\mu_0NI/L$, where $\mu_0$ is the permeability of free space. The only variable that changes in this scenario is the radius of the solenoid, which does not affect the magnetic field. Therefore, the magnetic field inside the solenoid will remain the same.

Question 16

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all other quantities remained the same, the magnetic field inside the solenoid will
A) remain the same.
B) become twice as strong as initially.
C) become one-half as strong as initially.
D) become four times as strong as initially.
E) become one-fourth as strong as initially.

Accepted Answer

The answer of Consider an ideal solenoid of length L,...

Question 17

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 4 cm from this wire?
A) 2 μT
B) 4 μT
C) 6 μT
D) 8 μT
E) 10 μT

Accepted Answer

The magnetic field created by a long straight current-carrying wire is given by:

B = μ0I/2πr

where B is the magnetic field at a distance r from the wire, I is the current flowing through the wire, and μ0 is the permeability of free space (4π × 10^-7 T·m/A).

Using the given information, we can solve for the current:

4 μT = μ0I/2π(0.02 m)

I = 2π(0.02 m)(4 μT)/μ0

I ≈ 10 A

Now we can use the above equation to find the magnetic field at a distance of 4 cm (0.04 m) from the wire:

B = μ0I/2πr = μ0(10 A)/2π(0.04 m) ≈ 2 μT

Therefore, the answer is A) 2 μT.

Question 18

A long straight wire has a constant current flowing to the right. A rectangular metal loop is situated above the wire, and also has a constant current flowing through it, as shown in the figure. Which one of the following statements is true? 
A) The net magnetic force on the rectangle is upward, and there is also a nonzero torque on the rectangle.
B) The net magnetic force on the rectangle is zero, and the net torque on it is zero.
C) The net magnetic force on the rectangle is downward, and there is also a nonzero torque on the rectangle.
D) The net magnetic force on the rectangle is zero, but there is a nonzero torque on the rectangle.
E) The net magnetic force on the rectangle is downward, and the net torque on it is zero.

Accepted Answer

The answer of A long straight wire has a constant...

Question 19

Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. If the magnetic field strength at the center of the smaller loop is B, what is the magnetic field strength at the center of the larger loop?
A) 8B
B) 4B
C) 2B
D) B/2
E) B/4

Accepted Answer

The answer of Consider two current-carrying circular loops. Both are...

Question 20

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop outside the loop, the magnetic field lines caused by this current
A) circle the loop in a clockwise direction.
B) circle the loop in a counterclockwise direction.
C) point straight up.
D) point straight down.

Accepted Answer

The answer of A current-carrying loop of wire lies flat...

Quiz 24: Magnetic Fields and Forces

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

A long straight wire carrying a 4-A current is placed along the x-axis as shown in the figure. What is the direction of the magnetic field at a point P due to this wire?

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop inside the loop, the magnetic field lines caused by this current

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

An electron traveling toward the magnetic north with speed 400 km/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 magnitude magnetic force acts on the electron? (e = 1.60 × 10^-19C)

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^-19C)

Which one of the following statements is correct?

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes

When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length and current) fixed, the magnetic field at the center of the solenoid will

A single current-carrying circular loop of radius R is placed next to a long, straight wire, as shown in the figure. The current I in the wire flows to the right. In which direction must current flow in the loop to produce a net magnetic field of zero at its center?

A proton moving at 5.0 × 10⁴ m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10^-19C)

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

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b) . A current I is flowing through the wire windings. If the radius of the solenoid is doubled to 2b, but all the other quantities remain the same, the magnetic field inside the solenoid will

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

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

A long straight wire has a constant current flowing to the right. A rectangular metal loop is situated above the wire, and also has a constant current flowing through it, as shown in the figure. Which one of the following statements is true?

Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. If the magnetic field strength at the center of the smaller loop is B, what is the magnetic field strength at the center of the larger loop?

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop outside the loop, the magnetic field lines caused by this current

Quiz 24: Magnetic Fields and Forces

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

A long straight wire carrying a 4-A current is placed along the x-axis as shown in the figure. What is the direction of the magnetic field at a point P due to this wire?

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop inside the loop, the magnetic field lines caused by this current

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

An electron traveling toward the magnetic north with speed 400 km/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 magnitude magnetic force acts on the electron? (e = 1.60 × 10-19C)

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 × 10-19C)

Which one of the following statements is correct?

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes

When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length and current) fixed, the magnetic field at the center of the solenoid will

A single current-carrying circular loop of radius R is placed next to a long, straight wire, as shown in the figure. The current I in the wire flows to the right. In which direction must current flow in the loop to produce a net magnetic field of zero at its center?

A proton moving at 5.0 × 104 m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10-19C)

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

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b) . A current I is flowing through the wire windings. If the radius of the solenoid is doubled to 2b, but all the other quantities remain the same, the magnetic field inside the solenoid will

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

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

A long straight wire has a constant current flowing to the right. A rectangular metal loop is situated above the wire, and also has a constant current flowing through it, as shown in the figure. Which one of the following statements is true?

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop outside the loop, the magnetic field lines caused by this current

An electron traveling toward the magnetic north with speed 400 km/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 magnitude magnetic force acts on the electron? (e = 1.60 × 10^-19C)

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^-19C)

A proton moving at 5.0 × 10⁴ m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10^-19C)