# Parallel plates - direction of electric field

• michaelw
In summary, the direction of the electric field between the plates of the parallel plate capacitor shown in the drawing would be up if the magnetic field is decreasing in time. This is because the induced current in the wire would be counterclockwise, creating a positive charge on the bottom plate and a negative charge on the top plate. To determine the strength of the E field, Gauss' Law would be used.

#### michaelw

Indicate the direction of the electric field between the plates of the parallel plate capacitor shown in the drawing if the magnetic field is decreasing in time. Give your reasoning.

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Try understanding the physics of the situation before asking the question so abruptly---

You would do well to recall Lenz Law... and with it, tell yourself what the direction the induced current in the wire will be (CW or CCW) ? Then decide how that would effect the E field between the capacitor plates.

Last edited:
not left hand :/?

Use left hand when dealing with electrons fired thru H fields :D

would the E field be up? (the magnetic field would be decreasing over time, so the induced magnetic field would have to oppsoe the change, and therefore point out of page. the current goes up when magnetic field points out, so the current will create a + charge on lower end of capacitor, - on upper, so E field points up)

current will go CCW right?? (god i hate conventional current)

Hehe, yep you're absolutely right... imagine some unknown entity wishing to fire extra H field upward, since the H field is decreasing... so in using your right hand, you want to point your thumb in the direction of that entity is wishing to fire the H field, and your fingers will naturally curl around in the direction the induced current is traveling... in this case it is CCW like you stated!

So yes, positive charge will accumulate on the bottom plate, and negative on the top... thus creating an E field going from the bottom plate to the top plate--- as for finding the strength of the E field... I doubt you'd be required to ever do that, however you'd analyze using Gauss and apply sigma/2epsilonnaught or whatnot.

## 1. What is the direction of the electric field between two parallel plates?

The electric field between two parallel plates is always perpendicular to the plates. It points from the positive plate to the negative plate.

## 2. Does the direction of the electric field change if the plates are charged with opposite charges?

Yes, the direction of the electric field will change if the plates are charged with opposite charges. The electric field will still be perpendicular to the plates, but it will now point from the positively charged plate to the negatively charged plate.

## 3. How does the distance between the plates affect the direction of the electric field?

The distance between the plates has no effect on the direction of the electric field. The electric field will always be perpendicular to the plates, regardless of the distance between them.

## 4. Is the direction of the electric field the same inside and outside of the plates?

No, the direction of the electric field is different inside and outside of the plates. Inside the plates, the electric field is perpendicular to the plates and points from the positive to the negative plate. Outside the plates, the electric field is perpendicular to the surface of the plates and points away from the plates in all directions.

## 5. How is the direction of the electric field related to the potential difference between the plates?

The direction of the electric field is related to the potential difference between the plates through the equation E = V/d, where E is the electric field, V is the potential difference, and d is the distance between the plates. The electric field always points from a higher potential to a lower potential.

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