Question

Select the incorrect statement
1) A wire is stretched to increase the length by 1%, the percentage change in resistance is 2%
2) Awire of resistance 'R' is stretched till its radius is half of the original value. Then the resistance of
stretched wire is '16R
3) A wire is stretched to double its length. Its resistance also doubles.
4) A piece of Cu and another Ge are cooled from room temperature to 80K. The resistance of Cu
decreases and Ge increases​

Answer 1

Answer:

4) is the incorrect statement friend !...hope it helps

Answer 2

Answer:

The incorrect statement is 3) A wire is stretched to double its length. Its resistance also doubles.

Explanation:

A wire is stretched to double its length.

Let initial length be L and length after stretching be L'.

L' = 2L

When a wire is stretched then its volume remains constant.

To keep volume constant, its area decreases.

Let initial area be A and area after stretching be A'.

A' = A/2

The expression for the resistance of a wire is given as,

R=ρ(L/A) where,

ρ is the resistivity of a material.

l is the length of wire.

A is the cross-sectional area.

After stretching, Resistance is given by

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

R' = $\rho\frac{2L}{\frac{A}{2} }$

R' = $\rho\frac{4L}{A}$

R' = 4ρ(L/A)

R' = 4R

Hence, on doubling the length of wire, the resistance of the wire becomes four times. (Not doubles)

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