### 2.05 Comparison between gravitational and electrical potential

To understand what we mean by voltage and electrical potential let us consider a similar example.   Consider an object which has been raised above the surface of the earth. If the object is released it will fall back towards the earth attracted by gravity. When the object is initially raised we provide it with energy (potential energy). When it falls this energy is released as it is converted to different forms. The higher the object is raised the more energy it will have to release when it falls. Also the more massive the object is the more energy it will have to released when it falls.
(We can appreciate either of the two previous facts by considering the damage that would be done when the object hits the ground.)

• As stated above, we say that the energy used to raise the object is stored as potential energy.
• The object falls when released due to gravity. Therefore we say that the object has gravitational potential energy.
• We have also stated that gravitational potential energy depends on the mass of the object as well as the height it is raised to.
• For a particular height above the Earth's surface we could calculate the amount of energy that would be supplied per each kilogram of the objects mass. This is called the gravitational potential. We just multiply this value by the mass of the object to calculate the gravitational potential energy.

In comparison with the above example,

• Instead of gravitational attraction we have attraction between negative electrons and the positive terminal of the battery.
• Instead of the mass of an object we have the electrical charge carried by each electron.
• Instead of gravitational potential we have electrical potential.

### Electrical potential, potential difference (p.d.)

Electrical potential is a measure of the electrical potential energy supplied to each coulomb of charge by the battery. Electrical potential is measured in volts. A potential difference is just the difference in the electrical potential between two points in a circuit.

p.d. = W/Q

• p.d. = potential difference measured in volts (V)
• W = work done (energy used) in moving the charge across the battery terminals
• Q = the quantity of charge moved across the battery terminals