JEE Physics 2026 Question with Solution

Given: The options are Voltage difference, Voltage, Resistance, and Displacement current.

Find: Which quantity is not measurable.

Concept: A measurable quantity is one that can be directly or indirectly measured using instruments. In electromagnetism, some quantities are theoretical constructs introduced for consistency of laws but are not directly measurable.

Step 1: Examine each option

• Voltage difference: Measured directly using a voltmeter.
• Voltage: Defined as potential difference; measurable using standard electrical instruments.
• Resistance: Measured using an ohmmeter or calculated using $V = IR$.
• Displacement current: Introduced by Maxwell to modify Ampère’s law. It does not correspond to actual flow of charge and cannot be measured directly.

Therefore, the correct option is D.