Question

Which of the following cannot be measured:

• A. Resistance
• B. Voltage
• C. Voltage difference
• D. Displacement current

Hint:

Voltmeters always measure {potential difference}, never the absolute electric potential at a single point.

Answer 1

The Correct Option is B

To determine which of the given options cannot be directly measured, we must understand what each parameter represents and how they are typically measured:

1. Resistance: It is a measure of the opposition to current flow in an electrical circuit. Resistance can be directly measured using a device called an ohmmeter or indirectly using a multimeter by applying Ohm's Law, which relates resistance (R), voltage (V), and current (I) as R = \frac{V}{I}.
2. Voltage: Voltage refers to the electric potential difference between two points. It is measured using a voltmeter. The term "voltage" commonly implies this potential difference, rather than an absolute measurement at one point.
3. Voltage Difference: This is essentially the same as voltage, as voltage is defined as the potential difference between two points. It is measured using a voltmeter by connecting its terminals at the two points of interest.
4. Displacement Current: This is a concept from Maxwell's equations, representing a form of current that flows in a dielectric medium when the electric field within it changes over time. Displacement current is not a physical current but a mathematical construct needed for the continuity of current in Maxwell's equations.

From this analysis, we conclude that:

• Resistance, voltage difference, and displacement current all pertain to conditions or phenomena that can be directly measured or calculated using known methods and instruments.
• Voltage, when considered as a single point value, cannot be measured directly since it is always a potential difference (i.e., requires two points for reference).

Thus, the correct answer is that Voltage cannot be directly measured as just a solitary point value; it must be regarded in terms of potential difference between two points.