The relative field strength of a coil is measured in which unit?

The relative field strength of a coil is measured in ampere turns because this unit directly relates to the magnetic field produced by a coil of wire when an electric current flows through it. Ampere turns is calculated by multiplying the current (in amperes) flowing through the coil by the number of turns of wire in the coil. This measure is essential in understanding how effectively a coil can generate a magnetic field, which depends on both the amount of current passed through the wire and the number of turns, hence highlighting the key role of ampere turns in electromagnetism.

The other units mentioned serve different purposes in electrical measurements. Volts measure electrical potential difference, Ohms quantify resistance in an electric circuit, and Watts represent the rate of energy consumption or power. Each of these units has its significance but does not specifically relate to the measurement of magnetic field strength created by a coil, making ampere turns the appropriate and relevant choice for this context.