You are Here: Home

# Charging a capacitor

Physics and electronics discussion, revision, exam and homework help.

Announcements Posted on
1. Charging a capacitor
In the diagram I is the charging current, E is the emf of the cell R a resistor and the plates are the capacitor with positive charge on one side negative on the other.

I'm a bit confused as to why the electrons are forced to accumulate on the plate connected to the negative side. Is this because the electrons flow from negative to positive, assuming the current flow is conventional current? Also how do the electrons get across the insulation, as they can't just jump across...
Attached Thumbnails

2. Re: Charging a capacitor

http://www.schoolphysics.co.uk/age16...rge/index.html
3. Re: Charging a capacitor
(Original post by SDA)

http://www.schoolphysics.co.uk/age16...rge/index.html
Hey thanks, it clears up some issues, but how do the electrons get onto the other plate, as they can't 'jump' across the insulation gap...
4. Re: Charging a capacitor
My understanding is that an electric field exists within the capacitor as a result of the different charges on the plates, electrons are able to move along electric field lines thus getting them from one plate to the other.
5. Re: Charging a capacitor
(Original post by SDA)
My understanding is that an electric field exists within the capacitor as a result of the different charges on the plates, electrons are able to move along electric field lines thus getting them from one plate to the other.
Ahh that makes sense!
6. Re: Charging a capacitor
(Original post by Emissionspectra)
Hey thanks, it clears up some issues, but how do the electrons get onto the other plate, as they can't 'jump' across the insulation gap...

(Original post by Emissionspectra)
Ahh that makes sense!
Electrons do NOT 'jump' across the gap in a theoretical capacitor. (There is leak current, but that's rarely considered in physics). The current across the capacitor is purely imaginary, and in a DC circuit, is zero.
7. Re: Charging a capacitor
(Original post by Xarren)
Electrons do NOT 'jump' across the gap in a theoretical capacitor. (There is leak current, but that's rarely considered in physics). The current across the capacitor is purely imaginary, and in a DC circuit, is zero.
Ok, so we have electrons piling up onto the capacitor plate on the negative side of the cell. And we get a positive charge on the positive side (assuming conventional current). But how do we get a complete circuit then, the current clearly ends back in the negative side of the cell; as shown in the diagram... is this correct so far?
8. Re: Charging a capacitor
Electrons are dragged from the top plate to the bottom plate by the electro-motive force created by the battery. There is no complete circuit. The current doesn't flow 'round and 'round.

The bigger the difference between the charges across the two plates, the more they are attracted to each other. Now if you draw this out again, you'll realise that this attraction works in the opposite direction to the EMF.

Once the EMF from the battery and the Potential Difference across the capacitor are equal, (Both measured in Volts), the flow of electrons stops, and the capacitor is fully charged up.
9. Re: Charging a capacitor
Bump.
10. Re: Charging a capacitor
(Original post by Xarren)
Electrons are dragged from the top plate to the bottom plate by the electro-motive force created by the battery. There is no complete circuit. The current doesn't flow 'round and 'round.

The bigger the difference between the charges across the two plates, the more they are attracted to each other. Now if you draw this out again, you'll realise that this attraction works in the opposite direction to the EMF.

Once the EMF from the battery and the Potential Difference across the capacitor are equal, (Both measured in Volts), the flow of electrons stops, and the capacitor is fully charged up.
Ahh, sorry I didn't see this post. That makes sense! thanks.

## Step 2: Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank

this is what you'll be called on TSR

2. this can't be left blank

never shared and never spammed

3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. By completing the slider below you agree to The Student Room's terms & conditions and site rules

2. Slide the button to the right to create your account

You don't slide that way? No problem.

Last updated: June 15, 2012
Study resources