In electrical science, what is the SI unit used to measure the electric resistance of a conductor?

Introduction / Context:
Electric resistance is a fundamental quantity in circuit theory, describing how strongly a component opposes the flow of electric current. It plays a key role in Ohm law and in calculating current, voltage, and power in electrical networks. This question asks you to recall the correct SI unit used to measure resistance.

Given Data / Assumptions:

• We are dealing with electric resistance of a conductor.
• The unit requested is the standard SI unit.
• The options list several different physical units.

Concept / Approach:
According to Ohm law, resistance R is defined by the relation: R = V / I where V is potential difference in volts and I is current in amperes. The SI unit of resistance is derived from this relation and is called the ohm, symbolised by the Greek letter omega in notation, but written as “ohm” in text. Other listed units, such as dyne, pascal, and joule, belong to different physical quantities.

Step-by-Step Solution:
Step 1: Recall Ohm law, which relates voltage, current, and resistance. Step 2: From R = V / I, note that units are volt per ampere. Step 3: Recognise that the SI unit corresponding to volt per ampere is named ohm. Step 4: Compare with the options and select ohm as the correct unit.

Verification / Alternative check:
In circuit diagrams and component specifications, resistances are given in ohms, kilo-ohms, or mega-ohms (for example, 100 ohm resistor, 1 kilo-ohm resistor). This consistent usage in electronics and physics confirms that ohm is the correct SI unit for resistance. None of the other units listed are ever used to describe resistance in standard practice.

Why Other Options Are Wrong:

• Dyne: This is a unit of force in the cgs system, not an SI unit and not related to resistance.
• Pascal: This is the SI unit of pressure, equal to one newton per square meter, and is unrelated to electrical resistance.
• Joule: This is the SI unit of energy or work, not of resistance.

Common Pitfalls:
Some students may confuse ohm with other electrical units such as volt or ampere, especially when learning multiple concepts at once. Remember that volts measure potential difference, amperes measure current, and ohms measure resistance. A helpful memory aid is the simple phrase from Ohm law: V (volt) = I (ampere) × R (ohm), which links all three units together.

Final Answer:
The SI unit of electric resistance is the ohm.