The energy stored in a coil, also known as an inductor, is measured in joules. This is because joules are the standard unit of measurement for energy in the International System of Units (SI). When an electric current flows through a coil, it creates a magnetic field, and energy is stored in that magnetic field. The amount of energy (in joules) can be calculated using the formula ( \text{Energy} = \frac{1}{2} L I^2 ), where ( L ) is the inductance in henries and ( I ) is the current in amperes.
Farads measure capacitance, which is not directly related to the energy stored in an inductor. Volts measure electrical potential difference, and amperes measure electric current. While both capacitors and inductors are key components in electronic circuits, their energy storage mechanisms are different, and the correct unit for the energy stored in a coil is indeed joules.