As the charge moves from point A to point B work is done, and the charge now has more potential energy
This can be represented by the equation below
The unit of potential difference is the Volt (V) which is a J/C
Potential Difference in a Uniform Electric Field
V = -Ed
The gap between electrodes in a spark plug is 0.060 cm. To produce an electric spark there must be an electric field of 3.0 x 10 6 V/m. What minimum potential difference must be applied to start a car?
The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge.
That's why the electronic flash on a camera uses a capacitor -- the battery charges up the flash's capacitor over several seconds, and then the capacitor dumps the full charge into the flash tube almost instantly.
This can make a large, charged capacitor extremely dangerous -- flash units and TVs have warnings about opening them up for this reason. They contain big capacitors that can, potentially, kill you with the charge they contain.
One of the more futuristic applications of capacitors is the capacitive touch screen. These are glass screens that have a very thin, transparent metallic coating.
A built-in electrode pattern charges the screen so when touched, a current is drawn to the finger and creates a voltage drop. This exact location of the voltage drop is picked up by a controller and transmitted to a computer.