What is the SI unit of resistance?
Ohm
Understanding the SI Unit of Resistance
The question asks about the Standard International (SI) unit for electrical resistance. Electrical resistance is a fundamental property of a material that opposes the flow of electric current.
What is Electrical Resistance?
Resistance quantifies how strongly a material resists the movement of electric charge. The higher the resistance, the more difficult it is for current to flow through the material for a given voltage. Ohm's Law relates voltage (V), current (I), and resistance (R) with the formula:
\(V = I \times R\)
where V is in volts, I is in amperes, and R is in ohms.
Identifying the SI Unit of Resistance
Let's look at the given options and their respective units in the SI system:
- Coulomb: This is the SI unit of electric charge. It measures the total amount of electrical charge.
- Siemens: This is the SI unit of electrical conductance. Conductance is the reciprocal of resistance (\(G = 1/R\)). It measures how easily current flows through a material.
- Ohm: This is the SI unit of electrical resistance. It is named after German physicist Georg Simon Ohm. The symbol for Ohm is \(\Omega\). One ohm is defined as the resistance between two points of a conductor when a constant potential difference of 1 volt applied to these points produces a current of 1 ampere, provided that the conductor is not the source of any electromotive force.
- Mho: This is an older, non-SI unit for electrical conductance. It is essentially the same as the Siemens (\(1 \text{ mho} = 1 \text{ Siemens}\)) and is spelled as "Ohm" backwards. Its symbol was \(\mho\), the inverted capital Greek letter Omega.
Based on the definitions, the SI unit specifically for electrical resistance is the Ohm.
| Quantity | SI Unit | Symbol |
|---|---|---|
| Electric Charge | Coulomb | C |
| Electric Potential Difference (Voltage) | Volt | V |
| Electric Current | Ampere | A |
| Electric Resistance | Ohm | \(\Omega\) |
| Electric Conductance | Siemens | S |
Therefore, the correct SI unit of resistance among the given options is Ohm.
Revision Table: Electrical Units
| Physical Quantity | SI Unit | Symbol | Relationship (Examples) |
|---|---|---|---|
| Electric Charge | Coulomb | C | Flow of 1A for 1s is 1C (C = A \(\times\) s) |
| Electric Current | Ampere | A | Rate of charge flow (A = C/s) |
| Voltage (Potential Difference) | Volt | V | Energy per unit charge (V = J/C) |
| Resistance | Ohm | \(\Omega\) | Opposition to current flow (R = V/I) |
| Conductance | Siemens | S | Ease of current flow (G = 1/R) |
| Energy | Joule | J | Work done (J) |
| Power | Watt | W | Rate of energy transfer (W = J/s = V \(\times\) I) |
Additional Information on Resistance and Conductance
Resistance and conductance are reciprocal properties. While resistance (\(R\)) measures how much a material opposes current, conductance (\(G\)) measures how easily current flows. The relationship is \(G = 1/R\).
Beyond resistance, materials also have properties called resistivity and conductivity:
- Resistivity (\(\rho\)): This is an intrinsic property of a material that indicates its resistance to current flow per unit length and cross-sectional area. The unit is Ohm-meter (\(\Omega \cdot \text{m}\)). Resistance of a conductor is given by \(R = \rho \times (L/A)\), where L is length and A is cross-sectional area.
- Conductivity (\(\sigma\)): This is the reciprocal of resistivity (\(\sigma = 1/\rho\)) and measures a material's ability to conduct electricity. The unit is Siemens per meter (\(\text{S}/\text{m}\)).
Understanding these units and properties is crucial for analyzing electric circuits and material behavior.
Important Questions from Units and Dimensional Formula
Which of the following is the SI base unit for photometry — the science of measuring light as perceived by the human visual system?
Which of the following units is used for measuring the amount of a substance?
What is the SI unit of pressure?
A. Newton per square centimetre (Newton per square centimetre)
B. Newton - Square Meter (Newton - Square Meter)
C. Newton per square meter (Newton per square meter)
D. Newton - Square centimetre (Newton - Square centimetre)
The SI number of power (power) is-
Which of the following have the same unit, ms-1 ?
