Questioning My Thinking: A Reflection

[polibuda]

Homework Statement

Determine the potential and electric field strength distribution inside the plate capacitor in the three cases.

1) The inside of the capacitor the space charge is equal to 0.

2) The interior of the flat capacitor contains an evenly distributed space charge qv.

3) The capacitor with homogeneous space charge qv. The capacitor plates are short-circuited.

Relevant Equations

E,V

I started to do this, but I'm not sure my thinking is good.

 

[BvU]

As per
https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/
we are not allowed to help until you post your own attempt at solution. (*)
And

I have no idea how to start do this

does not count

So until then you'll have to make do with e.g. one of the threads below

But it's not that difficult to find examples and modify them.

Tip: 'E, V' is not an equation.

(*) I'm not sure if that also excludes criticising the problem formulation , but I find 'space charge inside a capacitor' hard to understand. What do you think is meant?

 

[polibuda]

I have corrected my statement.

 

[BvU]

You leave a lot to guess by not explaining the symbols, but never mind.

At I)
What is your Gauss surface A ?
What is r ? What is d ?
Is E = 0 the only possible solution ?
Does it say V(d) = 0 ?

At II) and III) we really need some explanation what you are doing ...

 

[polibuda]

You leave a lot to guess by not explaining the symbols, but never mind.

At I)
What is your Gauss surface A ?
What is r ? What is d ?
Is E = 0 the only possible solution ?
Does it say V(d) = 0 ?

At II) and III) we really need some explanation what you are doing ...

So maybe we should focus only on the first case.
The Gauss surface is cylinder.
r is mistake, it should be d, which is the distance between two plates of capacitor.
I think if qv (space charge)=0 inside the capacitor, the field strength must be equal 0 due to formula:

V(d) is equal to U from source voltage.

 

[BvU]

Good plan to start with I) .

Basically you are saying there is no field in between the plates of a capacitor, no matter what voltage is applied !

The Gauss surface is cylinder.

A cylinder in a uniform E field also has $\int_V \rho\, dV = 0$ but definitely not E = 0 !

 

[polibuda]

Good plan to start with I) .

Basically you are saying there is no field in between the plates of a capacitor, no matter what voltage is applied ! A cylinder in a uniform E field also has $\int_V \rho\, dV = 0$ but definitely not E = 0 !

So I'm wrong, beacuse if the voltage exist (E=U/d), the field strength can't be equal to 0. But can you explain this formula. What is wrong?

A is coming from cylinder.

 

[BvU]

$\vec E \cdot d\vec A$ on one side is equal and opposite to $\vec E \cdot d\vec A$ on the other: they cancel out.

 

[polibuda]

Well, now I have no idea what I should to do. Could you advise me something?

 

[BvU]

start with I

and find a relevant equation in your notes or textbook