Assertion : When a wire is stretched so that its diameter is halved then its resistance become 16 times.
Reason : Resistance of wire decrease with increase in length.

Options

A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If both Assertion and Reason are false.

Answer

C

Explanation

The resistance of a wire is `R=(pl)/(A)` (1)
Hence, when the diameter is halved the resistance of the wire is
`Rprop1/((r/(2))^(2))=16R`
Hence, its resistance will become 16 times.
Again from eqn. (1),
`Rpropl/(A)orRpropl^(2)/(Al^(2))orRpropl^(2)`
Therefore, on increasing the length the resistance increases.