Potential difference

The voltage developed across the plates of the capacitor will not be instantaneous. It will be a reciprocal exponential function determined by the capacitance of the plates and the internal resistance of the cell. Capacitance is a function of the plate surface area, plate separation and the dielectric material between the plates. Internal resistance is a function of the chemical properties and physical construction of the cell.

What do you mean by 'uniform field'?

The pd developed across the capacitor plates is a measure of the energy stored in the electric force field between the plates. Current is a movement of charge (electrons), but no current needs to flow across the gap between the plates. All of the current flows in the conductors and is caused by the difference in charge on the capacitor plates and the battery electrodes.

I hate electricity, so i apologize if i ask basic questions.
How does a potential difference actual happen?

So long as something has electrons, if you apply a voltage will there be a current?

What i meant by the uniform field is an electric uniform field where the field lines are evenly spaced and separated so if the battery is 6V then 1 plate will be 6V and how would the other ever be anything other than 0V, this is primarily linked to the first question.

Voltage is a measure of the energy carried by the electrons - Joules per Coulomb.

Think of it like the pressure in a tank of water due to the height raised above ground. The gravitational potential energy of that water is mass x height x gravity.

So it is with electricity. Voltage is the 'pressure' pushing electrons around a circuit. But until the charge starts moving (current), the energy is still only potential energy.

When a current meets with a resistance, work is done by the electrons being forced through that resistance by votage pressure. Some of the energy of the electrons are converted to other forms of energy, like heat or photons and get carried away.


So once the electrons exit the reistance, they will have lost energy and have a new lower level of potential energy than which they started out with.

Voltage potential difference (pd) across a component, is a measure of the potential energy lost in traversing that resistance.

In water terms, it is a loss of pressure. i.e. the water pressure has dropped.

In voltage terms, there is a loss of voltage pressure. The voltage has dropped.


No. The electrons must be loosely bound to their atoms (conductors or semiconductors) or the electrons must already be free (thermionic emission for instance in a vacuum tube). The electrons bound to the nucleus of the atoms in an insulator, cannot be freed by the application of a voltage. No current can flow through the insulator.



Voltage is a relative measurement referenced to any point in a given circuit. See pressure analogy above.

It takes time for the charge to build up on the plates of the capacitor. The electrons carrying charge have to move there and that movement can be slowed by the presence of a resistance in the current path.

But as the charge builds up, the repulsive force generated across the gap between the electrons on the opposite plate also increases. As it does so, new electrons arriving find it harder and harder to push agaist the building repulsion, until at some point, there is not enough voltage pressure to force any more onto the plate.

So the voltage developed across the capacitor is measure of the potential energy stored.

At first, there is no resistance to the inrush of current. There is hardly any energy stored in the capicitor and therefore the potential difference across the plates is very small.

Quickly, as more electrons rush in, the repulsive forces between the plates increases. A back pressure develops which slows the inrush of new electrons until it eventually is cut off. It takes longer and longer for the charge on the plates to continue building.

Hence the reciprocal exponential part of charge build up and voltage developed.