Question

Assertion: The resistance of a given mass of copper wire is inversely proportional to the square of length.
Reason: when a copper wire of given mass is stretched to increase its length, its cross- sectional area of decreases.

Answer 1

Answer:

Also the resistance of a conductor is inversely proportional to its cross-sectional area (A) as R ∝ 1/A. Thus doubling its cross-sectional area would halve its resistance, while halving its cross-sectional area would double its resistance.

Explanation:

I hope it's helpful to you!!

Answer 2

Assertion is false but reason is true.

Explanation:

• Resistance is defined as an obstacle in the path of flow of current.

• There is an opposition in current flow which is provided by a passive electric component.

• Resistances obey Ohm's Law: $V=IR$

where V is the potential difference applied across the load and I is the current flowing in the load.

• Resistance in inversely proportional to the area of cross section and directly proportional to the length of conductor.

• Resistance is also defined as: $R=$ρ$\frac{L}{A}$

where $L$ is the length of the resistor, $A$ is the area of cross sectional area of the resistor and ρ is the resistivity of the material of resistor.

• Now, the resistance of a given mass of copper wire is inversely proportional to the square of radius of cross section because $A=\pi r^{2}$ and resistance is inversely proportional to area.
• And when a copper wire of given mass is stretched to increase its length, its cross- sectional area of decreases because there is a relation of direct proportionality.