In the International System of Units (SI), what is the unit used to measure electrical resistance?

Introduction / Context:

This general physics question is about SI units for basic electrical quantities. Electrical resistance describes how strongly a material opposes the flow of electric current. Using the correct unit symbol is important for interpreting circuit diagrams, formulas, and specifications of electrical components such as resistors and wires.

Given Data / Assumptions:

• We are dealing with electrical resistance R in Ohm’s law, where V = I * R.
• The question asks specifically for the SI unit of resistance.
• Other SI units mentioned are those of force, charge, and energy.

Concept / Approach:

Ohm’s law relates voltage V (in volts), current I (in amperes), and resistance R by V = I * R. From this, resistance can be expressed as R = V / I. In SI units, the unit of resistance is defined as one volt per ampere and is given the special name ohm, with symbol capital Greek letter omega. Other units such as newton, coulomb, and joule correspond to force, electric charge, and energy respectively, not resistance.

Step-by-Step Solution:

Verification / Alternative check:

Any resistor component is labelled with a value such as 10 ohm, 1 kiloohm, or 1 megaohm, using the symbol omega to indicate resistance. Circuit analysis textbooks always list the SI units for basic quantities as volt for voltage, ampere for current, and ohm for resistance. This consistent usage across physics and electrical engineering confirms that ohm is the correct unit for resistance.

Why Other Options Are Wrong:

• Newton: SI unit of force, defined from F = m * a.
• Coulomb: SI unit of electric charge, related to current by Q = I * t.
• Joule: SI unit of energy or work, used in equations such as W = F * s or E = P * t.

Common Pitfalls:

Students sometimes mix up Coulomb and ohm because both are linked to electricity. However, Coulomb refers to the quantity of charge, while ohm refers to how much a component resists current flow. Others confuse ohm with volt or ampere. Remembering the Ohm’s law triangle (V, I, R) and associating ohm with resistance, volt with potential difference, and ampere with current helps avoid these errors.

Final Answer:

The SI unit of electrical resistance is the ohm.