2. State and explain Ohm's law.

3. How does the resistance of a conductor vary with its (i) length and (ii) area of cross section?

4. Mention the expression for resistance in terms of resistivity and explain the terms.

5. Define electrical resistivity of a conductor. Mention its SI unit.

6. Mention any two factors on which resistivity of a metal depend.

7. Write any two differences between resistance and resistivity.

8. Define electrical conductivity of a conductor. Mention its SI unit.

9. Define current density in a conductor. Mention its SI unit.

Ohm's Law states that current is directly proportional to voltage and inversely proportional to resistance. Resistance varies with length and area of cross-section, while resistivity is an intrinsic property of materials measured in ohm-meters. Electrical conductivity is the ability of a material to conduct electricity, and current density is the amount of current per unit area, measured in amperes per square meter.
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Answered by Anonymous | 2025-07-04

Ohm's Law : Ohm's Law states that the current (I) through a conductor between two points is directly proportional to the voltage (V) across the two points, provided the temperature remains constant. This can be expressed by the formula:
V = I R
where:

V is the voltage across the conductor (volts).
I is the current flowing through the conductor (amperes).
R is the resistance of the conductor (ohms).


Resistance Variation with Length and Cross-Sectional Area :

(i) Length : The resistance of a conductor is directly proportional to its length. This means that if the length of the conductor is increased, its resistance will increase.
(ii) Area of Cross-Section : The resistance is inversely proportional to the area of its cross-section. Thus, a larger cross-sectional area results in lower resistance.


Expression for Resistance in Terms of Resistivity : The resistance R of a conductor can be expressed in terms of its resistivity ρ as follows:
R = ρ A L ​
where:

ρ is the resistivity of the material (ohm-meter).
L is the length of the conductor (meters).
A is the cross-sectional area of the conductor (square meters).


Definition of Electrical Resistivity : Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. It is a material property and is measured in ohm-meters ( Ω ⋅ m ).

Factors Affecting Resistivity :

Temperature: Increasing temperature generally increases the resistivity of metals.
Material Composition: Different materials have different intrinsic resistivities.


Differences between Resistance and Resistivity :

Resistance is a measure of the opposition to current flow in a specific object and depends on the object's dimensions and material; resistivity is a measure of a material's opposition to current flow, independent of its shape and size.
Resistance is measured in ohms ( Ω ); resistivity is measured in ohm-meters ( Ω ⋅ m ).


Electrical Conductivity : Electrical conductivity is the measure of a material's ability to conduct electric current and is the reciprocal of resistivity. Its SI unit is siemens per meter (S/m).

Current Density : Current density is the amount of electric current flowing per unit area of a cross-section. It is given by the formula:
J = A I ​
where:

J is the current density (amperes per square meter).
I is the current (amperes).
A is the cross-sectional area (square meters).

Its SI unit is amperes per square meter (A/m²).

Answered by BenjaminOwenLewis | 2025-07-06