The question asks us to identify which among the given options is not a measurable quantity. Let's examine each option:
Voltage difference: It is the difference in electric potential between two points in an electric field. Voltage is measured in volts (V) using a voltmeter. Therefore, it is a measurable quantity.
Voltage: Similarly, voltage itself, which is the potential difference between two points, is measured in volts (V) and is a standard measurable quantity.
Resistance: Resistance is a measure of the opposition to current flow in an electrical circuit. It is measured in ohms (Ω) using an ohmmeter. Hence, it is also a measurable quantity.
Displacement current: This concept arises in Maxwell's equations, representing a form of current that compensates for the changing electric field in the absence of a real charge flow. It is theoretically described and part of the analysis of electromagnetic fields, but it is not a directly measurable quantity like the others listed. It is inferred through calculations and associated effects.
Considering the reasoning above, the correct answer is:
Displacement current, which is not a direct measurable quantity.
