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Capacitor charge and Volatge.

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Electronman

New Member
Hi,

In a Capacitor the more numbers of charges means the more voltage saved in the capacitor.
If we connect a 100uF and a 1000uF cap to 10V source then we know that more charges will be on the bigger cap, then why both caps have 10V across them? While the bigger one has more charges ( maybe ie more voltage)?
 

Sceadwian

Banned
Capacitance is a voltage potential with a certain number of charge carriers present. There is more energy available at the same voltage from a capacitor that can hold a higher number of charge carriers. This should be self evident.
 

BrownOut

Banned
Because voltage in a capacitor is proportional to the charge in the cap divided by the value of the cap. So, the bigger cap has the same voltage as the smaller one although it has more charge, because the ratio of charge to capacitance is the same.
 

MikeMl

Well-Known Member
Most Helpful Member
Voltage is NOT charge:

One coulomb is the amount of charge stored by a capacitance of one farad charged to a potential difference of one volt:

A 100uF capacitor charged to 10V contains 100e-6*10 = 1e-3 COULOMBs.
A 1000uF capacitor charged to 10V contains 1000e-6*10 = 1e-2 COULOMBs, or ten times more charge.
 

ke5frf

New Member
Voltage and charge are related but different as has been pointed out.

Here is a non-math way of understanding this...


I have two compressors running that are delivering the same flow (in cubic centimeters per/minute) of air into two compressed air cylinders.

The two cylinders are different sizes. One is twice as big as the other in VOLUME. It will hold twice as much air....but this is KEY, twice as much air at THE SAME PRESSURE. If the cylinders are said to be "empty", they actually DO have air in them, only at atmospheric pressure (equalized).

Turn on the compressors. It will take TWICE AS LONG for the larger cylinder to reach the same pressure as the small one, despite having the same flow of air going in.

So a STORED CYLINDER (think capacitor) which is twice as big at X pressure has twice the number of air molecules as a half size cylinder at the same pressure.

A large capacitor holding x number of NEGATIVELY CHARGED PARTICLES will be HALF THE VOLTAGE of a capacitor that is half its size with the same number (x) of charged particles.

If the Larger capacitor is fully charged to twice the charge of the smaller capacitor, they will have the same voltage.

Voltage is PRESSURE.
Charge is unit per area/volume...as a percentage of capacity given a certain pressure.

It is really easy when you think of it this way.
 
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