Volt

The volt ($\mathrm{V}$) is the derived SI unit for Voltage and Electric potential difference.

A potential difference of one volt means each coulomb of Charge gains or loses one Joule of Energy when it moves between two points:

$$1\mathrm{V}=1\frac{\mathrm{J}}{\mathrm{C}}$$

That is the most useful intuition: voltage is energy-per-charge, not energy by itself. A $12\mathrm{V}$ battery can give $12\mathrm{J}$ to each coulomb of charge that passes through the circuit, but the total energy depends on how much charge moves.

Using Coulomb as $\mathrm{A}\mathrm{s}$ and Joule as $\mathrm{kg}{\mathrm{m}}^2{\mathrm{s}}^{-2}$:

$$1\mathrm{V}=1\mathrm{kg}{\mathrm{m}}^2{\mathrm{s}}^{-3}{\mathrm{A}}^{-1}$$

Equivalent forms worth recognising:

$$P=IV\Rightarrow 1\mathrm{V}=1\frac{\mathrm{W}}{\mathrm{A}}$$ $$E=QV\Rightarrow 1\mathrm{J}=1\mathrm{C}\mathrm{V}$$

Common mistake: saying “voltage flows”. Current flows; voltage is the energy difference per unit charge that can drive that current.

Quick check: if a circuit question asks for energy, voltage alone is insufficient. You also need charge, current-time, or power-time information.

Quick check

A volt is a joule per coulomb:

$$1\mathrm{V}=1\mathrm{J}{\mathrm{C}}^{-1}.$$

So voltage is energy per unit charge. A $9\mathrm{V}$ battery can provide about $9\mathrm{J}$ of energy for every coulomb of charge moved through the circuit, ignoring losses/internal resistance.