Question 1

At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:

Accepted Answer

The electron will experience a force perpendicular to both its velocity and the magnetic field, given by the Lorentz force law. In this case, the force will be in the negative y direction since v is in the positive x direction and B is in the positive z direction. This force will cause the electron to undergo circular motion in the xy plane, with the direction of the rotation determined by the right-hand rule. Since the force is in the negative y direction, the electron will rotate counterclockwise around a circle in the xy plane when viewed from the positive z axis.

Question 2

The diagram shows a straight wire carrying a flow of electrons into the page. The wire is between the poles of a permanent magnet. The direction of the magnetic force exerted on the wire is:

Accepted Answer

The answer of The diagram shows a straight wire carrying...

Question 3

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

Accepted Answer

The answer of The current is from left to right...

Question 4

Electrons (mass m, charge -e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field  that is perpendicular to their velocity. The radius of the resulting electron trajectory is:

Accepted Answer

The answer of Electrons (mass m, charge -e) are accelerated...

Question 5

J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular  fields, gave the value of:

Accepted Answer

J. J. Thomson's experiment involved measuring the deflection of an electron beam in mutually perpendicular electric and magnetic fields. By varying the strength of the fields, he was able to determine the charge-to-mass ratio (e/m) of the electron. Therefore, the correct choice is D, which is the charge-to-mass ratio for the electron.

Question 6

A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:

Accepted Answer

The answer of A current is clockwise around the outside...

Question 7

The figure shows a uniform magnetic field  directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

Accepted Answer

According to the right-hand rule, the force on a current-carrying wire in a magnetic field is perpendicular to both the field direction and the current direction. In this case, the current is into the page and the field is directed to the left, so the force will be upward, toward the top of the page.

Question 8

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

Accepted Answer

The answer of The diagram shows a straight wire carrying...

Question 9

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially:

Accepted Answer

The magnetic force on a charged particle is given by $F = qvB\sin(\theta)$, where $q$ is the charge, $v$ is the velocity, $B$ is the magnetic field strength, and $\theta$ is the angle between the velocity and the magnetic field. Since the electron and proton have equal and opposite charges and are moving at the same speed in the same direction relative to the magnetic field, the magnitudes of their forces will be equal, but the directions will be opposite due to their opposite charges.

Question 10

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field  is:

Accepted Answer

The answer of The magnetic torque exerted on a flat...

Question 11

An ion with a charge of +3.25*10⁻¹⁹ C is in region where a uniform electric field of 5 * 10^4.V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be:

Accepted Answer

The answer of An ion with a charge of +3.25*10⁻¹⁹...

Question 12

An electron is launched with velocity in a uniform magnetic field The angle $\theta$between is between 0 and 90^o. As a result, the electron follows a helix, its velocity vector returning to its initial value in a time interval of:

Accepted Answer

The answer of An electron is launched with velocity ...

Question 13

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

Accepted Answer

First, we need to find the magnetic force on each side of the triangle. We can use the formula:
F = BILsinθ
where F is the magnetic force, B is the magnetic field, I is the current, L is the length of the wire, and θ is the angle between the wire and the magnetic field.

For the two equal sides of the triangle, the angle between the wire and the magnetic field is 90 degrees, so sinθ = 1. For the hypotenuse, the angle between the wire and the magnetic field is 45 degrees, so sinθ = sin(45) = 0.707.

For each of the equal sides:
F = (0.7 T)(2.0 A)(0.15 m)(1) = 0.21 N

For the hypotenuse:
F = (0.7 T)(2.0 A)(0.15 m)(0.707) = 0.30 N

Since the magnetic force on the two equal sides is in opposite directions and has the same magnitude, they cancel out each other. Therefore, the resultant magnetic force is simply the magnitude of the force on the hypotenuse:
Resultant F = 0.30 N

So the answer is C, 0.30 N.

Question 14

A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:

Accepted Answer

The answer of A cyclotron operates with a given magnetic...

Question 15

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

Accepted Answer

The answer of A loop of wire carrying a current...

Question 16

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field  parallel to the side MK as indicated. The loop will tend to rotate:

Accepted Answer

The answer of A square loop of wire lies in...

Question 17

The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:

Accepted Answer

The answer of The figure shows the motion of electrons...

Question 18

An electron and a proton both each travel with equal speeds around circular orbits in the same uniform magnetic field, as shown in the diagram (not to scale). The field is into the page on the diagram. Because the electron is less massive than the proton and because the electron is negatively charged and the proton is positively charged:

Accepted Answer

The answer of An electron and a proton both each...

Question 19

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields  The beam then enters a region of another magnetic field  perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

Accepted Answer

The answer of In a certain mass spectrograph, an ion...

Question 20

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

Accepted Answer

The spiral motion is caused by the magnetic force, which is always perpendicular to the velocity of the charged particle. As the particle spirals inward, its speed must be decreasing, and since the magnetic force is always perpendicular to the velocity, the acceleration due to the magnetic force must also be perpendicular to the velocity. This means that the magnetic force must be acting towards the center of the spiral, which requires the charge to be negative. Therefore, the best choice is B, the charge is negative and slowing down.

Quiz 28: Magnetic Fields

At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

Electrons (mass m, charge -e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field that is perpendicular to their velocity. The radius of the resulting electron trajectory is:

J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular fields, gave the value of:

A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:

The figure shows a uniform magnetic field directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially:

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field is:

An ion with a charge of +3.2510⁻¹⁹ C is in region where a uniform electric field of 5 10^4.V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be:

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field parallel to the side MK as indicated. The loop will tend to rotate:

The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields The beam then enters a region of another magnetic field perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

Quiz 28: Magnetic Fields

At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:

The diagram shows a straight wire carrying a flow of electrons into the page. The wire is between the poles of a permanent magnet. The direction of the magnetic force exerted on the wire is:

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

Electrons (mass m, charge -e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field that is perpendicular to their velocity. The radius of the resulting electron trajectory is:

J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular fields, gave the value of:

A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:

The figure shows a uniform magnetic field directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially:

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field is:

An ion with a charge of +3.25*10−19 C is in region where a uniform electric field of 5 * 104. V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be:

An electron is launched with velocity in a uniform magnetic field The angle θ\thetaθ between is between 0 and 90o. As a result, the electron follows a helix, its velocity vector returning to its initial value in a time interval of:

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field parallel to the side MK as indicated. The loop will tend to rotate:

The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields The beam then enters a region of another magnetic field perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

An ion with a charge of +3.2510⁻¹⁹ C is in region where a uniform electric field of 5 10^4.V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be: