In what unit is the energy stored in a coil measured?

The energy stored in a coil, commonly found in inductors, is measured in henrys. The henry is the SI unit of inductance, which quantifies how effectively a coil or inductor can store energy in its magnetic field when current passes through it.

When a current flows through a coil, it creates a magnetic field, and the energy stored in that magnetic field is directly related to the inductance (in henrys) and the amount of current flowing through the coil (in amperes). The relationship can be expressed using the formula for energy stored in an inductor:

[ W = \frac{1}{2} L I^2 ]

Where W is the energy in joules, L is the inductance in henrys, and I is the current in amperes. This formula illustrates that the energy stored is contingent on the inductance value, which is measured in henrys, making this unit the correct answer for the question.

The other options refer to different concepts in electrical measurements: volts measure electric potential, amperes measure the flow of electric current, and watts measure power (the rate of energy transfer). These do not pertain to the specific measurement of energy stored in the magnetic field of a coil.