What is the unit of voltage and what does one volt represent?

• A. One volt equals one joule per coulomb.
• B. One volt equals one watt.
• C. One volt equals one joule.
• D. One volt equals one ampere.

Answer: (A)

Voltage is the electrical potential difference, the energy change that occurs when a small amount of charge moves between two points. The volt is defined as one joule of energy per one coulomb of charge, so when a charge of 1 coulomb moves through a potential difference of 1 volt, 1 joule of energy is transferred. This is why one volt equals one joule per coulomb.

The other options don’t fit because a watt is energy per time (power), a joule is total energy (not per charge), and an ampere is current (charge flow per second).