Unit of Specific Resistance - Definition, Resistance Vs Electrical Resistance, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:39 PM IST

Resistance Definition:
In an electric circuit, resistance could be a measure of the opposition to current flow.

What is Specific Resistance?

Specific Resistance:- When a voltage is applied to a substance, its specific resistance to a current is defined as the resistance provided by a unit length and unit cross-section of the substance. The unit of specific resistance is Ω m. Specific resistance, often known as electrical resistivity, is a measurement of a particular element's conductivity.

Unit of Specific Resistance - Definition, Resistance Vs Electrical Resistance, FAQs

The Specific resistance of a conducting substance can be stated mathematically as,

$\rho=\frac{R A}{L}$

Where,

R denotes the conductor's resistance.

L is the conductor's length.

A = conductor's cross-sectional area.

ρ = the material's proportionality constant, often known as its specific resistance or resistivity.

The Ohm-meters (Ω m) is the unit of specific resistance.

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Specific Resistance Vs Electrical Resistance

A material's specific resistance is an inherent property that is determined by its composition. However, the electrical resistance is an intrinsic property that is determined by the conductor's length and cross-section, as well as the applied potential difference. Ohm (. m) is the SI unit for specific resistance is ohm-meters (Ω m), whereas Ohm is the SI unit for electrical resistance.

Specific Resistance Definition

When a voltage is applied to a substance, its specific resistance to a current is defined as the resistance provided by a unit length and unit cross-section of the substance.

The formula of specific resistance

The Specific resistance of a conducting substance can be stated mathematically as,

$\rho=\frac{R A}{L}$

Where,

R denotes the conductor's resistance.

l is the conductor's length.

a = conductor's cross-sectional area.

ρ = the material's proportionality constant, often known as its specific resistance or resistivity.

The Ohm-meters (Ω m) is the unit of specific resistance.

Related Topics Link,

SI unit of specific resistance / Unit of Specific resistance

The Ohm-meters (Ω m) is the unit of specific resistance.

Ohm-meter symbol: Ω m

Factors affecting the specific resistance

Specific resistance is dependent upon the temperature, composition, and pressure of the material. Temperature affects specific resistance. The specific resistance of various materials increases as the temperature rises. The resistance of such elements is considered as having a positive coefficient of temperature. It will increase for such elements as the temperature rises. Similarly, as the temperature rises, the resistance of particular elements decreases. The coefficient of such elements is considered to be negative. The resistance of such elements decreases as the temperature rises.

Specific Resistance of some materials:

The specific resistances of copper at 200C

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Value: 1.68*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

The specific resistances of silver at 200C

Value: 1.59*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

The specific resistances of iron at 200C

Value: 9.70*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

Also Read:

The specific resistances of platinum at 200C

Value: 1.06*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

The specific resistances of gold at 200C

Value: 2.44*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

The specific resistances of Tin at 200C

Value: 1.09*10^-8
Type: conductor
Unit of specific resistance: ohm-meters

The specific resistances of Glass at 200C

Value: 10¹¹-10¹⁵
Type: insulators
Unit of specific resistance: ohm-meters

The specific resistances of Rubber at 200C

Value: 10¹³
Type: insulators
Unit of specific resistance: ohm-meters

The specific resistances of a Diamond at 200C

Value: 10¹²
Type: insulator
Unit of specific resistance: ohm-meters

The specific resistances of air at 200C

Value: 10⁹-10¹⁵
Type: insulator
Unit of specific resistance: ohm-meters

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NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. What is resistance reciprocal?

Conductance is the reciprocal of resistance.

2. Write the difference between the electrical resistance and the Specific Resistance of a material?

A material's specific resistance is an inherent property that is determined by its composition. However, resistance is an intrinsic property that is determined by the conductor's length and cross-section, as well as the applied potential difference. Ohm (. m) is the SI unit for specific resistance is ohm-meters (Ω m), whereas Ohm is the SI unit for resistance.

3. What is the Copper Conductor's Specific Resistance Value?

Copper has a very low specific resistance, with a value of 1.68* 10-8 Ω m at 20°C. Copper is a good conductor of electricity due to its low resistivity. As a result of its low specific resistance, copper is preferred in most electrical wiring.

4. Which material has a high specific resistance value?

The resistivity of glass is approximately 1014. Glass is usually formed when molten material cools too quickly to form a regular crystal lattice. Most of the common glasses are made of the same chemical composition as quartz.

5. Why is the unit of specific resistance ohm-meter (Ω·m)?

The unit of specific resistance is ohm-meter (Ω·m) because it represents the resistance of a cube of material with sides of 1 meter. This unit combines resistance (ohms) with length (meters) to create a measure that is independent of the object's size and shape.

6. How does specific resistance affect the choice of materials for electrical wiring?

Materials with low specific resistance, like copper and aluminum, are preferred for electrical wiring because they allow current to flow easily, reducing energy loss. The specific resistance helps engineers calculate the appropriate wire gauge and material for different applications, balancing factors like conductivity, cost, and weight.

7. How does the concept of specific resistance apply to electrolytes?

In electrolytes, specific resistance depends on the concentration and mobility of ions rather than electrons. As the concentration of ions increases, the specific resistance generally decreases. However, at very high concentrations, ion-ion interactions can increase specific resistance.

8. Why is specific resistance important in the design of heating elements?

Specific resistance is crucial in designing heating elements because it determines how efficiently the material converts electrical energy into heat. Materials with higher specific resistance, like nichrome, are often used because they generate more heat for a given current, making them more effective for heating applications.

9. How does specific resistance affect the power dissipation in a conductor?

Materials with higher specific resistance dissipate more power as heat when current flows through them. The power dissipated is proportional to the resistance, which is directly related to the specific resistance. This relationship is crucial in designing circuits and choosing appropriate materials to manage heat generation.

10. What is specific resistance, and how is it different from electrical resistance?

Specific resistance, also called resistivity, is a material property that measures how strongly a material opposes the flow of electric current. It is independent of the object's size and shape. Electrical resistance, on the other hand, depends on both the material and the object's dimensions. Specific resistance is measured in ohm-meters (Ω·m), while electrical resistance is measured in ohms (Ω).

11. Why do different materials have different specific resistances?

Different materials have different specific resistances due to their atomic and electronic structures. Factors such as the number of free electrons, atomic spacing, and crystal structure all influence how easily electrons can move through the material, determining its specific resistance.

12. How does the specific resistance of a semiconductor compare to that of a metal?

Semiconductors generally have higher specific resistance than metals. Metals have many free electrons, allowing for easy current flow, while semiconductors have fewer charge carriers. However, the specific resistance of semiconductors can be significantly altered by doping or temperature changes.

13. Can specific resistance ever be zero?

In theory, perfect conductors like superconductors have zero specific resistance. However, in practice, all materials at normal temperatures have some level of specific resistance. Superconductors only achieve zero resistance under specific conditions, such as extremely low temperatures.

14. How is specific resistance related to conductivity?

Specific resistance is the inverse of electrical conductivity. Materials with high specific resistance have low conductivity, and vice versa. The relationship is expressed as σ = 1/ρ, where σ is conductivity and ρ is specific resistance.

15. How does temperature affect specific resistance?

Temperature generally increases the specific resistance of metals due to increased atomic vibrations, which impede electron flow. For semiconductors, higher temperatures can decrease specific resistance by exciting more charge carriers. The relationship between temperature and specific resistance is often linear for small temperature changes.

16. How is specific resistance measured experimentally?

Specific resistance is typically measured using a four-point probe method. This involves passing a known current through the material and measuring the voltage drop across a known distance. By applying the material's dimensions to the measured values, the specific resistance can be calculated using the relationship between resistance, length, and cross-sectional area.

17. What's the relationship between specific resistance and thermal conductivity?

In metals, there's often an inverse relationship between specific resistance and thermal conductivity, known as the Wiedemann-Franz law. Materials that are good electrical conductors (low specific resistance) tend to be good thermal conductors as well. This relationship arises because free electrons in metals contribute to both electrical and thermal conduction.

18. What's the relationship between specific resistance and the Hall effect?

The Hall effect and specific resistance are both related to charge carrier movement in materials. The Hall effect can be used to determine the type and concentration of charge carriers, which in turn affect the specific resistance. Materials with low specific resistance often exhibit a weak Hall effect due to the high concentration of charge carriers.

19. What's the relationship between specific resistance and the Kondo effect in certain materials?

The Kondo effect, observed in some materials with magnetic impurities, can cause an anomalous increase in specific resistance at low temperatures. This occurs due to the scattering of conduction electrons by localized magnetic moments. Understanding this relationship is important in studying strongly correlated electron systems and certain types of magnetic materials.

20. How does specific resistance relate to the concept of hopping conduction in disordered materials?

In disordered materials, where electrons can't move freely, conduction often occurs through a process called hopping. This mechanism leads to a different temperature dependence of specific resistance compared to band conduction in crystalline materials. Understanding this relationship is important for materials like amorphous semiconductors and conducting polymers.

21. What's the relationship between specific resistance and the cross-sectional area of a wire?

Specific resistance is independent of the wire's cross-sectional area. However, the electrical resistance of a wire is inversely proportional to its cross-sectional area. A thicker wire (larger cross-sectional area) made of the same material will have lower electrical resistance but the same specific resistance.

22. Can specific resistance be negative?

No, specific resistance cannot be negative. It's always a positive quantity because it represents the opposition to current flow. A negative value would imply that the material generates energy rather than resisting current flow, which violates the laws of thermodynamics for normal materials.

23. What's the difference between specific resistance and resistivity?

There is no difference; specific resistance and resistivity are two terms for the same property. Both refer to the intrinsic ability of a material to resist the flow of electric current, independent of its size and shape.

24. How does the specific resistance of a material relate to its band gap in solid-state physics?

Materials with larger band gaps generally have higher specific resistance. In insulators and semiconductors, the band gap represents the energy required for electrons to move from the valence band to the conduction band. A larger band gap means fewer electrons can participate in conduction, resulting in higher specific resistance.

25. Can the specific resistance of a material change over time?

Yes, the specific resistance of a material can change over time due to factors like oxidation, contamination, or structural changes. For instance, the specific resistance of metals can increase as they oxidize or corrode. In some cases, aging or environmental factors can alter a material's specific resistance.

26. What's the relationship between specific resistance and the mean free path of electrons?

The mean free path of electrons is inversely related to specific resistance. A longer mean free path indicates that electrons can travel further before colliding with atoms or impurities, resulting in lower specific resistance. Materials with shorter mean free paths have higher specific resistance due to more frequent collisions.

27. How does specific resistance affect the skin effect in conductors?

Specific resistance influences the skin effect, where alternating current tends to flow near the surface of a conductor. Materials with lower specific resistance experience a more pronounced skin effect, as the current is more easily confined to the surface. This effect becomes more significant at higher frequencies and in materials with lower specific resistance.

28. Why isn't specific resistance always constant for a given material?

Specific resistance can vary due to factors like temperature, pressure, and impurities. In some materials, it can also depend on the direction of current flow (anisotropy). Additionally, in semiconductors, specific resistance can change dramatically with doping levels or applied electric fields.

29. How does specific resistance relate to the drift velocity of electrons in a conductor?

Specific resistance is inversely related to drift velocity. Materials with higher specific resistance have lower drift velocities for a given electric field strength. This is because the increased resistance impedes the motion of electrons through the material.

30. Can specific resistance be used to identify unknown materials?

Yes, specific resistance can be used as one method to identify unknown materials or assess material purity. Each material has a characteristic specific resistance, which can be measured and compared to known values. However, this method is often used in conjunction with other techniques for more accurate identification.

31. How does the specific resistance of a composite material relate to its components?

The specific resistance of a composite material depends on the specific resistances of its components and their arrangement. For materials in parallel, the overall specific resistance is lower than any individual component. For materials in series, the overall specific resistance is higher. The exact relationship depends on the volume fractions and distribution of the components.

32. What's the significance of specific resistance in the context of superconductivity?

In superconductivity, the specific resistance drops to zero below a critical temperature. This phenomenon allows for the flow of electric current with no energy loss. The transition to zero specific resistance is a key characteristic of superconductors and is fundamental to their unique properties and applications.

33. How does specific resistance affect the choice of materials for electrical contacts?

Materials with low specific resistance are preferred for electrical contacts to minimize power loss and heat generation at the contact point. However, other factors like hardness, corrosion resistance, and cost are also considered. Gold, silver, and copper are common choices due to their low specific resistance and other favorable properties.

34. How does specific resistance affect the operation of strain gauges?

Strain gauges rely on changes in specific resistance when a material is deformed. As the gauge is stretched or compressed, its specific resistance changes slightly. This change is used to measure strain in the material. The sensitivity of a strain gauge depends on how much its specific resistance changes with deformation.

35. Why is the specific resistance of semiconductors more sensitive to temperature than that of metals?

The specific resistance of semiconductors is more temperature-sensitive because temperature changes affect the number of charge carriers. In metals, the number of free electrons remains relatively constant with temperature. In semiconductors, higher temperatures excite more electrons from the valence to the conduction band, significantly decreasing specific resistance.

36. How does specific resistance relate to the concept of mobility in semiconductor physics?

Specific resistance is inversely proportional to the product of charge carrier concentration and mobility. In semiconductors, both these factors can vary significantly with temperature and doping. Higher mobility or carrier concentration leads to lower specific resistance. This relationship is crucial in understanding and engineering semiconductor devices.

37. What role does specific resistance play in the design of electrical fuses?

Specific resistance is crucial in fuse design. Fuses are made of materials with specific resistance that allows them to heat up and melt when current exceeds a certain level. The choice of material and its specific resistance determines the fuse's current rating and response time. Materials with higher specific resistance heat up more quickly for a given current.

38. How does the concept of specific resistance apply to 2D materials like graphene?

In 2D materials like graphene, the concept of specific resistance is adapted to account for the material's two-dimensional nature. Instead of ohm-meters, it's often expressed in ohms per square (Ω/□). The specific resistance of graphene can be extremely low, making it an excellent conductor, but it can vary significantly based on factors like substrate interaction and defects.

39. What's the significance of specific resistance in the context of thermoelectric materials?

In thermoelectric materials, a balance between low specific resistance and low thermal conductivity is desired. Low specific resistance allows for efficient electrical conduction, while low thermal conductivity maintains a temperature gradient. The ratio of these properties contributes to the material's thermoelectric figure of merit, which determines its efficiency in converting heat to electricity or vice versa.

40. How does specific resistance affect the choice of materials for electromagnetic shielding?

Materials with low specific resistance are generally preferred for electromagnetic shielding because they can more effectively reflect and absorb electromagnetic waves. However, the ideal specific resistance can vary depending on the frequency of the radiation being shielded. In some cases, materials with moderate specific resistance are used to absorb rather than reflect radiation.

41. How does specific resistance affect the performance of electrical capacitors?

While capacitors primarily store charge, the specific resistance of their materials affects their performance. Lower specific resistance in the conductive plates reduces energy loss and improves the capacitor's efficiency. However, in the dielectric material between the plates, higher specific resistance is desirable to prevent current leakage and maintain charge storage.

42. What's the significance of specific resistance in the context of electrical grounding systems?

Low specific resistance is crucial for effective electrical grounding. The ground itself acts as a conductive medium, and its specific resistance affects how well it can dissipate electrical charge. Soil with lower specific resistance provides better grounding. This is why grounding systems often use materials like copper or chemical treatments to reduce the effective specific resistance of the soil.

43. How does specific resistance relate to the concept of relaxation time in electron transport theory?

Relaxation time, which represents the average time between electron collisions, is inversely related to specific resistance. Materials with longer relaxation times have lower specific resistance because electrons can travel further before scattering. This concept is fundamental to understanding electron transport in solids and is closely tied to the Drude model of electrical conduction.

44. What role does specific resistance play in the functioning of photoresistors?

In photoresistors, the specific resistance changes in response to light intensity. When light strikes the photoresistor, it generates charge carriers, decreasing the material's specific resistance. This change in specific resistance is used to detect and measure light intensity. The relationship between light intensity and specific resistance is key to the operation of these devices.

45. How does the concept of specific resistance apply to plasma?

In plasma, the concept of specific resistance is more complex due to the presence of both ions and electrons. The specific resistance of plasma depends on factors like temperature, density, and the degree of ionization. Unlike in solid conductors, the specific resistance of plasma can decrease with increasing temperature due to increased ionization.

46. What's the relationship between specific resistance and the Seebeck coefficient in thermoelectric materials?

The Seebeck coefficient and specific resistance are both important in thermoelectric materials. Generally, a high Seebeck coefficient and low specific resistance are desirable for efficient thermoelectric conversion. However, these properties are often inversely related, so optimizing thermoelectric materials involves finding the best balance between them.

47. How does specific resistance affect the choice of materials for electrical bus bars?

Bus bars require materials with very low specific resistance to minimize power loss and heat generation when carrying large currents. Copper and aluminum are common choices due to their low specific resistance. The specific resistance helps determine the required size and shape of the bus bar for a given current capacity.

48. What's the significance of specific resistance in the design of electrical heating pads?

In heating pads, materials with higher specific resistance are often used because they generate more heat for a given current. The specific resistance determines how much electrical energy is converted to heat. Designers must balance the specific resistance with other factors like durability and flexibility to create effective and safe heating pads.

49. How does specific resistance relate to the concept of mean free time in electron transport?

Mean free time, the average time between electron collisions, is inversely proportional to specific resistance. Materials with longer mean free times have lower specific resistance because electrons can travel further without scattering. This concept is crucial in understanding how electron transport properties relate to a material's specific resistance.

50. What role does specific resistance play in the functioning of bolometers?

Bolometers rely on changes in specific resistance with temperature to detect radiation. When radiation is absorbed, it heats the bolometer material, changing its specific resistance. This change is measured to determine the amount of incident radiation. Materials with a high temperature coefficient of resistance (large change in specific resistance with temperature) are ideal for bolometers.

51. How does the concept of specific resistance apply to quantum materials like topological insulators?

In topological insulators, the bulk material has high specific resistance like an insulator, but the surface conducts electricity with very low specific resistance. This unique property arises from topologically protected surface states. The interplay between bulk and surface specific resistance is crucial in understanding and utilizing these materials in quantum electronics.

52. How does specific resistance affect the choice of materials for electrical contacts in MEMS devices?

In Micro-Electro-Mechanical Systems (MEMS), the choice of contact materials is crucial. Low specific resistance is desirable to minimize power loss and heat generation in these small-scale devices. However, other factors like wear resistance and compatibility with microfabrication processes also play important roles. The balance between these factors often leads to the use of specialized alloys or coatings.

53. What's the significance of specific resistance in the context of organic semiconductors?

In organic semiconductors, specific resistance can be much higher than in inorganic semiconductors and can vary widely based on molecular structure and arrangement. Understanding and controlling specific resistance is crucial for developing organic electronic devices. The relationship between molecular structure and specific resistance is an active area of research in organic electronics.