# Magnetism and Electric Potential Problem

• bbbbbev
In summary, the conversation is about finding the uniform magnetic field that allows an electron to travel in a straight line between two parallel plates with different potentials. The person is trying to solve the problem by finding the velocity of the electron and using the equation F = qvBsin(phi), but they are unsure if they are approaching the problem correctly. After going through the calculations, they get a value for the magnetic field, but it is not accepted as the correct answer. They ask for help and mention the direction of the magnetic field, but they are still unsure of their answer.
bbbbbev
Hi. I'm having some trouble with this problem:

An electron accelerated from rest through potential difference 1.6 kV enters the gap between two parallel plates having separation 20.0 mm and potential difference 120 V. The lower plate is at the lower potential. Neglect fringing and assume that the electron's velocity vector is perpendicular to the electric field vector between the plates. What uniform magnetic field allows the electron to travel in a straight line in the gap?

I was thinking that all I really needed to do was figure out the velocity of the electron and plug all the values into the equation

F = qvBsin(phi)

phi = 90 degrees in this problem, so the equation can just be written as

F = qvB

To find v, I used the fact that change in kinetic energy = change in potential energy.

KE = PE

(1/2)mv^2 = q(deltaV)

v = sqrt((2q(deltaV))/m)

After plugging in all the numbers I got:

v = sqrt(2(1.6e-19C)(1600V)/(9.11e-31kg))

v = 2.37e7 m/s

When I plug that into the magnetic field equation I get:

B = F/qv, so B = Eq/qv. Since E = V/d and the q's cancel, I then used

B = V/(distance)(v)

B = (120 V)/(0.02 m)(2.37e7m/s) = 2.53e-4 T

But that was not the correct answer. I know this is a lot of work to look through, but I'd appreciate any help anyone could give me because I'm really not sure I'm looking at this problem correctly. What am I missing.

Thanks,

Beverly

you got the value of B correct, but you must be careful about hte direction of the magnetic field. Since the magenetic field obeys the right hand rule which way should hte magnetic field point?

I think the magnetic field is in the k direction, which is to the left, but I don't think that value for B is right. I put that in as my answer (on webassign), and it counted it wrong. I don't know what else to try! Thanks for you help! Beverly

## 1. What is the difference between magnetism and electric potential?

Magnetism is the force that attracts or repels objects based on their magnetic properties, while electric potential is the potential energy per unit charge of an electric field.

## 2. How do magnets and electric potential interact?

Magnets and electric potential can interact in a variety of ways, such as when a magnetic field is created by an electric current or when electric potential is induced by a changing magnetic field.

## 3. What are some practical applications of magnetism and electric potential?

Magnetism and electric potential have many practical applications, including generators, motors, MRI machines, and speakers. They are also used in everyday objects such as credit cards and computer hard drives.

## 4. Can magnetism and electric potential be used to produce clean energy?

Yes, both magnetism and electric potential can be harnessed to produce clean energy. Examples include hydroelectric power plants, wind turbines, and solar panels.

## 5. How do I solve problems involving magnetism and electric potential?

To solve problems involving magnetism and electric potential, you will need to use equations such as Coulomb's Law and the Biot-Savart Law. It is also important to understand the behavior of electric and magnetic fields, as well as the properties of different materials.

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