# Calculating Magnetic Forces on a Current Loop in a Uniform Field

• Jon Wilson
In summary, the conversation discusses a problem involving an electron moving through electric and magnetic fields and the steps to determine the magnitude of the fields. At time t1, an electron is sent along the positive direction of the x axis, with an electric field E directed parallel to the y axis and a magnetic field B. The graph given in Figure 28-34 shows the y component Fnet,y of the net force as a function of the electron's speed v at time t1. The x and z components of the net force are both zero at t1. The conversation then goes on to discuss the steps to determine the magnitude of E and B, including using the formula v=E/B and considering the direction of the force and motion. The
Jon Wilson
i have a question that i need some help with:

at time t1, an electron is sent along the positive direction of an x axis, through both an electric field E and a magnetic field B, with E directed parallel to the y axis. Figure 28-34 gives the y component Fnet, y of the net force of the electron due to the two fields, as a function of the electron's speed v at time t1. the x and z components of the net force are zero at t1. Assuming Bx=0, find the magnitude E and B in unit-vector notion.

Not enough information given for anyone else to do the problem without the figure. What have you done to try to solve this?

there is a graph that has v as the x-axis and Fnet as the y-axis. it is a line that goes from x=0, y=-2 to x=50, y=0 to x=75, y=1. i know in ties into the formula v=E/B and possiably F=(qv)B. what i don't know is how to figure out what B is, if i knew how to do that i would be able to figure out the problem.

the best i could come up with is E= -1.25x10^-38 N/C and B= (2.5x10^-2 T) ^k

Jon Wilson said:
i have a question that i need some help with:

at time t1, an electron is sent along the positive direction of an x axis, through both an electric field E and a magnetic field B, with E directed parallel to the y axis. Figure 28-34 gives the y component Fnet, y of the net force of the electron due to the two fields, as a function of the electron's speed v at time t1. the x and z components of the net force are zero at t1. Assuming Bx=0, find the magnitude E and B in unit-vector notion.

Jon Wilson said:
there is a graph that has v as the x-axis and Fnet as the y-axis. it is a line that goes from x=0, y=-2 to x=50, y=0 to x=75, y=1. i know in ties into the formula v=E/B and possiably F=(qv)B. what i don't know is how to figure out what B is, if i knew how to do that i would be able to figure out the problem.

You are given that the fields are

$$\overrightarrow E = E_y \widehat j$$

$$\overrightarrow B = B_y \widehat j + B_z \widehat k$$

You know that the electric force is independent of velocity, so when you look at the graph where the velocity is zero, the net force must be from the electric field alone. You are also told that there is no net force in the x and z directions. What you must do is determine from the direction of the force, and the direction of the motion, which component of the magnetic field is producing the magnetic force. From the force versus velocity graph, you can determine the amount of force being contributed by the magnetic field for any velocity. You can pick one velocity (for example, the one that yields zero net force overall) and find the corresponding magnetic force (remember, the electric force is constant) and use that to determine the strength of the magnetic field.

thanks for the explination. I have one more question for you:

A single-turn current loop, carrying a current of 4 A, is in the shape of a right triangle, with sides 50 cm, 120 cm, and 130 cm. The loop is in a uniform magnetic field of magnitude 75 mT whose direction is parallel to the current in the 130 cm side of the loop. What is the magnitude of the magnetic force on (a)the 130 cm side, (b) the 50 cm side, and (c) the 120 cm side? (d) What is the magnitude of the net force on the loop?

I worked it out and the answers I got were: (a) Fb= 0 (b) .0138 N (c) .0138 N (d) 0. Does this look correct to you?

Jon Wilson said:
thanks for the explination. I have one more question for you:

A single-turn current loop, carrying a current of 4 A, is in the shape of a right triangle, with sides 50 cm, 120 cm, and 130 cm. The loop is in a uniform magnetic field of magnitude 75 mT whose direction is parallel to the current in the 130 cm side of the loop. What is the magnitude of the magnetic force on (a)the 130 cm side, (b) the 50 cm side, and (c) the 120 cm side? (d) What is the magnitude of the net force on the loop?

I worked it out and the answers I got were: (a) Fb= 0 (b) .0138 N (c) .0138 N (d) 0. Does this look correct to you?

a) is correct. b) and c) should not be the same, so d) cannot be right. How are you doing b) and c)?

## 1. What is a magnetic field?

A magnetic field is a region in space where magnetic forces can be detected. It is created by moving electric charges, such as electrons, and is a fundamental property of magnetism.

## 2. How is a magnetic field measured?

A magnetic field is measured using a device called a magnetometer, which can detect the strength and direction of the magnetic field. There are different types of magnetometers, such as compasses and Hall effect sensors, that are used for different purposes.

## 3. What are the uses of magnetic fields?

Magnetic fields have a wide range of uses in various fields, including technology, medicine, and research. They are used in compasses, motors, generators, MRI machines, particle accelerators, and many other applications.

## 4. How can magnetic fields be created or changed?

Magnetic fields can be created by moving electric charges, such as through the flow of electricity or the rotation of the Earth. They can also be changed by the presence of other magnetic fields or by changing the electric current or magnetic material in a specific area.

## 5. What are the effects of magnetic fields on living organisms?

While magnetic fields have been shown to have some biological effects on certain organisms, the magnitude and significance of these effects are still being studied. Some organisms, such as birds and turtles, are believed to use magnetic fields for navigation, while other studies have shown potential links between magnetic fields and health effects in humans.

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