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WHAT IS VOLTAGE (OR POTENTIAL DIFFERENCE)? A battery has chemical potential energy. Energy (E) is measured in joules (J). Chemical reactions in a battery energize and separate electrons from atoms. The negative terminal of the battery produces energized electrons. The positive terminal lacks electrons. When the switch on a circuit is closed, the energized electrons move from the negative terminal, through a load and return to the positive terminal with no remaining energy. The chemical energy from the battery is converted to light energy in a light bulb. 3. Electrons return to positive terminal with no energy left 1. Energized electrons leave the negative terminal 2. Electrons give up their energy to the load Potential difference: The easiest way to think about what batteries do is to use a water analogy. Batteries ‘lift’ electric charges to a higher potential. There is a potential difference between one end of a battery to the other. The electric charges with higher potential energy can now do work, by flowing ‘downhill’ through a load. Potential difference is the difference in potential energy per coulomb of charge between two points in the circuit. Potential difference is also called voltage or electric potential. Potential difference is measured in volts by a voltmeter. Which of these figures illustrates higher potential difference or voltage? Variable Variable Symbol Unit Unit Symbol Potential difference or voltage V volts V energy E joules J electric charge Q coulomb C NOTE: Potential difference or voltage is the only variable where the symbol for the units is the same as the symbol for the variable.