# Electric force between 2 parallel plates

• Oblivion77
In summary, the conversation discusses how to find the speed of an electron as it emerges from an electric field. The initial velocity of the electron is given, and the distance it travels is known. The conversation mentions using kinematic equations and the electric force equation to determine the acceleration and ultimately the speed of the electron. However, it is pointed out that the magnitude of the electric field is not necessary to solve the problem and that the horizontal velocity and distance can be used to calculate the time taken for the electron to reach the end of the plates. After some discussion and clarification, it is determined that the correct equation to use is t = s/v, and the correct units for time are m/(m/s) = s.
Oblivion77

## Homework Statement

An electron is projected with an initial velocity of 1.6x10$$^{6}$$ m/s. If the electron just misses the upper plate as it emerges from the field, find the speed of the electron as it emerges from the field?

## Homework Equations

Electric force equation

## The Attempt at a Solution

I am stuck trying to figure out the magnitude of the electric field, once I can figure this out I know how to solve the problem. Any pointers on how to find the magnitude of the electric field?

Use ordinary kinematic means to determine the velocity.

You know the speed, hence how long for it to emerge.

In that time you also know the deflection so you can determine the acceleration.

That acceleration then yields the additional sideways component of velocity to calculate it's speed at that point right?

Oblivion77 said:
I am stuck trying to figure out the magnitude of the electric field, once I can figure this out I know how to solve the problem. Any pointers on how to find the magnitude of the electric field?
You don't need to know the magnitude of the electric field.

I was planning to use Vf^2 = Vo^2 +2ad to find the final velocity, but I am missing the acceleration component. To find the acceleration I wanted to use F = ma (knowing the mass of the electron). But I would need the magnitude of the electric field to find the force from E = F / q.

So how would I do this without using the electric field? I don't know what you mean about using the "deflection" to find the acceleration. How would I calculate that?

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Oblivion77 said:
So how would I do this without using the electric field?

The horizontal velocity to the end of the plate gives you time.

Use the distance, acceleration, time relationship to determine acceleration.

Then you can use your V2, acceleration and distance.

Thanks for the advice, but this does not work. I get the answer wrong, the magnitude of the electric field is 364N/C, I am just not sure how to find it. When I use this electric field with the method I stated above I get the right answer. I just can't figure out how they got 364N/C :(

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Once you determine the acceleration from the trajectory, then you can use f = ma to determine field intensity.

They ask really though for just the speed.

That equals (Vx2 +Vy2)1/2

LowlyPion said:
Once you determine the acceleration from the trajectory, then you can use f = ma to determine field intensity.

They ask really though for just the speed.

That equals (Vx2 +Vy2)1/2

Yes! Thank you so much, I figured it out now =)

I wondered if that wasn't it.

Good luck.

Please will someone explain how I am meant to calculate the time taken for the electron to reach the end of the plates. I'm just not getting it.

you have the horizontal distance and the velocity in x-direction is constant, so t = v / s

oh dear. that was rather dense of me. thank you! :)

You're welcome ^^

songoku said:
you have the horizontal distance and the velocity in x-direction is constant, so t = v / s

Sorry, I'm not getting the right answer..not sure where I'm going wrong..should it not be t=s/v because t=v/s yields an answer of 80,000,000

NamrataJ said:
Sorry, I'm not getting the right answer..not sure where I'm going wrong..should it not be t=s/v because t=v/s yields an answer of 80,000,000
To check if an equation makes sense, look at the units. t = v/s → (m/s)/s = m/s^2; these are units of acceleration, not time, so this equation makes no sense.

Since v = s/t, t = s/v is correct. The units would be m/(m/s) = m(s/m) = s. Makes sense.

oh sorry, it's my mistake
it should be t = s/v

thank you :)

You're welcome
sorry for the mistake earlier ^^

## What is the electric force between two parallel plates?

The electric force between two parallel plates is a type of electrostatic force that exists between two charged plates that are parallel to each other. It is a force that acts in the direction perpendicular to the plates and is directly proportional to the magnitude of the charges on the plates and inversely proportional to the distance between them.

## How is the electric force between two parallel plates calculated?

The electric force between two parallel plates can be calculated using the formula F = Q * E, where F is the force, Q is the magnitude of the charges on the plates, and E is the electric field strength between the plates. The electric field strength can be calculated using the formula E = V/d, where V is the potential difference between the plates and d is the distance between them.

## What factors affect the electric force between two parallel plates?

The electric force between two parallel plates is affected by the magnitude of the charges on the plates, the distance between the plates, and the type of material the plates are made of. It is also affected by the presence of other charges or objects in the surrounding environment, as they can alter the electric field between the plates.

## What is the relationship between the electric force and the distance between two parallel plates?

The electric force between two parallel plates is inversely proportional to the distance between them. This means that as the distance between the plates increases, the electric force between them decreases. This relationship is known as the inverse square law.

## Can the direction of the electric force between two parallel plates change?

Yes, the direction of the electric force between two parallel plates can change depending on the charges on the plates. If the plates have opposite charges, the force will be attractive and will pull the plates towards each other. If the plates have the same charge, the force will be repulsive and will push the plates away from each other.

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