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Unit of Resistance

Unit of Resistance

Vishal kumarUpdated on 02 Jul 2025, 04:39 PM IST

When studying electric currents, students frequently come across the term "resistance." While there are two elements that affect electric current, conductance and resistance, we will focus on the latter on this page. When it comes to resistance, it's simply described as the impediment that a substance creates in the flow of electric current and it is denoted by the letter R. We'll look at the resistance unit and other details further down. The unit of resistance is the ohm.

Unit of Resistance
Unit of Resistance

What is the unit of resistance?

SI unit of resistance in physics or unit of resistance in physics:

The ohm, which is defined as a volt per ampere, is the si unit of resistance. In honour of German physicist George Simon Ohm, the name has been preserved. The unit is sometimes written as a word or represented by the Greek letter omega in uppercase.

Also read -

Specific resistance-

A conductor's resistance R is dependent on its length L, cross-section A, and composition. The resistance is proportional to the length of the conductor for a certain cross-section. Whereas the resistance of the cross-section for a certain length is inversely proportional. The two dependencies can be combined as,

R ∞ L/A

R = p L/A

Here constant proportionality is known as the specific resistance. The strength of a homogenous chunk of a unit-length and cross-sectional material is defined as the strength or resistance of a material. Quantitatively,

p = R A/L

The specific resistance unit SI is Ohm (mode of resistance).

Ohm’s law-

Ohm's law states that the relationship between current, voltage, and resistance. The amount of steady current through a large number of materials is directly proportional to the potential difference, or voltage, across the materials. Ohm's law may be expressed mathematically as

I∝V

The continuous proportionality of,

R = V/I

R is known as the conducting wire's resistance, depending on the physical condition and structure of the material in question.

Related Topics Link,

Commonly Asked Questions

Q: Can resistance ever be zero?
A:
In practice, all normal materials have some resistance. However, superconductors, which are materials cooled to extremely low temperatures, can exhibit zero electrical resistance. This phenomenon allows current to flow without any energy loss.
Q: How does the concept of resistance relate to Ohm's Law?
A:
Ohm's Law states that V = IR, where V is voltage, I is current, and R is resistance. This means resistance is the ratio of voltage to current (R = V/I). Ohm's Law forms the foundation for understanding how resistance affects current flow in electrical circuits.
Q: What is a potentiometer and how does it relate to resistance?
A:
A potentiometer is a variable resistor with three terminals. It allows for adjustment of resistance by moving a sliding contact along a resistive element. Potentiometers are used to control voltage in circuits, such as volume controls in audio equipment.
Q: Can resistance be negative?
A:
In conventional resistors, resistance is always positive. However, in some special devices like tunnel diodes or in certain conditions like in plasma physics, a negative differential resistance can occur. This doesn't mean the total resistance is negative, but that the resistance decreases as current increases in a specific operating range.
Q: What is the difference between AC and DC resistance?
A:
DC resistance is the resistance to direct current, which is constant. AC resistance, also called impedance, includes resistance to alternating current and can vary with frequency due to inductive and capacitive effects in the circuit.

Si unit of resistance-

The si unit of resistance is the ohm (Ω).

International ohm unit definition-

1 Ohm is the resistance of a mercury column with a temperature of melting ice, a uniform cross-sectional area, a length of 106.3 cm, and a mass of 14.4521 g.

Also Read:

NEET Highest Scoring Chapters & Topics
This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.
Download E-book

Some popular SI units-

Abohm, megohm, statohm and Planck-impedance are some of the most used resistance units. Take a look at the conversion chart below.

Conservation to ohms

Abohm
1.10^{-9}ohm
Stat coulomb0.00001c2ohms
Preece1.106ohms
Megohm1000000ohms

Some important points-

  • Temperature-dependent resistance. If there is a consistent holding of other physical amounts, resistance increases with increasing metal temperature. The resistivity decreases significantly for glass, however, at very high temperatures.
  • In the superconducting state, superconductors have zero resistance (at very low temperatures).
  • The resistance of semiconductors decreases as the temperature increases.

Also check-

NCERT Physics Notes:

Commonly Asked Questions

Q: What is the unit of electrical resistance?
A:
The unit of electrical resistance is the ohm (Ω). One ohm is defined as the resistance that allows one ampere of current to flow when one volt of potential difference is applied across it.
Q: Why is resistance measured in ohms?
A:
Resistance is measured in ohms to honor Georg Ohm, who discovered the relationship between voltage, current, and resistance (Ohm's Law). The ohm provides a standardized unit for quantifying how much a material opposes the flow of electric current.
Q: What's the difference between resistance and resistivity?
A:
Resistance is a property of a specific object, measured in ohms (Ω), while resistivity is a property of the material itself, measured in ohm-meters (Ω⋅m). Resistivity is independent of the object's size or shape, whereas resistance depends on both the material and the object's dimensions.
Q: What is the relationship between conductance and resistance?
A:
Conductance is the reciprocal of resistance. It measures how easily current flows through a material. The unit of conductance is the siemens (S), which is equivalent to 1/ohm. As resistance increases, conductance decreases, and vice versa.
Q: How does the size of a resistor affect its resistance?
A:
Generally, increasing the length of a resistor increases its resistance, while increasing its cross-sectional area decreases its resistance. This is because resistance is directly proportional to length and inversely proportional to area.

Frequently Asked Questions (FAQs)

Q: What is the concept of "resistance matching" in audio systems?
A:
Resistance matching, more broadly known as impedance matching, is crucial in audio systems for maximizing power transfer and minimizing signal distortion. It involves ensuring that the output impedance of a source (like an amplifier) is properly matched to the input impedance of a load (like speakers). Proper matching ensures efficient power transfer and maintains the intended frequency response of the system.
Q: How does the concept of resistance apply to human body safety with electricity?
A:
The human body has its own electrical resistance, typically between 1,000 to 100,000 ohms depending on conditions. This resistance can limit current flow through the body, but it's not always enough to prevent injury. Understanding body resistance helps in designing safety measures for electrical systems and in comprehending the dangers of electric shock.
Q: What is meant by "internal resistance" in a battery?
A:
Internal resistance in a battery refers to the opposition to current flow within the battery itself. It's caused by the electrochemical processes and physical structure of the battery. As internal resistance increases (often with battery age or use), the battery's ability to deliver current decreases, reducing its effective voltage under load.
Q: How does resistance relate to the concept of electrical insulators?
A:
Electrical insulators are materials with very high resistance to electric current flow. They have resistances typically greater than 10^8 Ω⋅m. This high resistance prevents significant current flow, making insulators useful for protecting against electric shock and for separating conductive components in electrical systems.
Q: What is a thermistor and how does it utilize the principle of resistance?
A:
A thermistor is a type of resistor whose resistance changes significantly with temperature. There are two types: NTC (Negative Temperature Coefficient) where resistance decreases with increasing temperature, and PTC (Positive Temperature Coefficient) where resistance increases with temperature. Thermistors are used in temperature sensing and control applications.
Q: How does resistance affect the charging and discharging of a capacitor?
A:
The resistance in a circuit with a capacitor determines the rate at which the capacitor charges or discharges. A higher resistance results in a slower charging/discharging rate, while a lower resistance allows for faster charging/discharging. This relationship is described by the time constant τ = RC, where R is resistance and C is capacitance.
Q: How does the resistance of a wire change if its length is doubled but its diameter is halved?
A:
If a wire's length is doubled and its diameter is halved, its resistance increases by a factor of 8. This is because resistance is directly proportional to length and inversely proportional to cross-sectional area. Doubling the length doubles the resistance, and halving the diameter quarters the cross-sectional area, further quadrupling the resistance.
Q: What is a strain gauge and how does it use the principle of resistance?
A:
A strain gauge is a sensor that measures strain (deformation) of an object by detecting changes in electrical resistance. When the gauge is stretched or compressed, its resistance changes slightly. This change in resistance is proportional to the strain, allowing for precise measurements of stress, weight, pressure, or other forces causing deformation.
Q: What is contact resistance and why is it important in electrical connections?
A:
Contact resistance is the additional resistance that occurs at the interface between two conducting surfaces in an electrical connection. It's important because it can lead to voltage drops and power losses, especially in high-current applications. Minimizing contact resistance through proper connection techniques and materials is crucial for efficient electrical systems.
Q: What is the significance of the resistance-temperature coefficient?
A:
The resistance-temperature coefficient describes how the resistance of a material changes with temperature. It's usually expressed as a percentage change per degree Celsius. Materials with a positive coefficient (like most metals) increase in resistance as temperature rises, while those with a negative coefficient (like some semiconductors) decrease in resistance. This property is crucial in designing temperature-sensitive devices and compensating for temperature effects in circuits.
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