# The Force on an Electron ?

• edlin
In summary: However, if the B field also exists outside of the circle, then the qv X B force will still act on the particle.

#### edlin

The Force on an Electron...??

Again, hi! I am very thankful for the help that I am being provided. I am yet again stuck in a problem.

I really do not understand it.

For the situation described in Figure P31.32, the magnetic field changes with time according to the expression B = (5.00t3 - 1.00t2 + 0.800) T, and r2 = 2R = 5.00 cm.

(I have also attached the image).

Right now, I have not really tried to solve it, because I want to understand the concept first, but I really don't get it...mostly because I am not sure what equations would be appropriate.

(1) I have thought the equation for electric force would be useful, since they do involve an electron in the problem, and it's what we want to find. Fe = qE.

By deriving B in the problem, is it correct to say that I got the E field? (Which would therefore allow me to get the Force)

(2) Then I saw in the section where this problem appeared, that they use another type of equation for the E field, which is:

E = -r/2 * dB/dt

I don't believe that using just these equations in (1) and (2) will give me the right answer though, but after that I don't know what else I am supposed to assume or do.

(3) Also, since the r2 is outside of the circle in the image, I am assuming this is important. But I don't know how to include this in the problem.

I guess that mostly it's the concept that I don't understand. I really appreciate any help that I may get. Thankyou!

#### Attachments

• p31-32.gif
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The general vector force on a charged particle in a combination E and B field is

$$F = (q E) + (q v X B)$$

Does that help?

I did see that equation though, but I'm not sure how I would get the velocity.

And does it matter that r is outside the circle??

The velocity of the charged particle is changed by the F=ma force on it. The force on the charged particle comes from the qE + qv X B forces acting on it. And you are correct, if the B only exists insice that circle, then the qv X B force goes away outside the circle.

## 1. What is the force on an electron?

The force on an electron is the measure of the influence that other particles or objects have on the electron's movement or behavior.

## 2. How is the force on an electron calculated?

The force on an electron is calculated using the formula F = qE, where F is the force, q is the charge of the electron, and E is the electric field strength.

## 3. What factors can affect the force on an electron?

The force on an electron can be affected by the electric field strength, the distance from other particles or objects, and the charge of those particles or objects.

## 4. Can the force on an electron be negative?

Yes, the force on an electron can be negative if the electric field strength is in the opposite direction of the electron's motion.

## 5. How does the force on an electron differ from the force on a proton?

The force on an electron differs from the force on a proton in terms of direction and magnitude. Electrons are negatively charged and will be repelled by other negative charges, while protons are positively charged and will be attracted to negative charges. Additionally, the force on an electron is much smaller compared to the force on a proton due to the difference in their masses.