The length and area of cross section of a conductor are doubled, then its resistance is

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Halved

Unchanged

Doubled

Quadrupled

answer is B.

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Detailed Solution

Concept: The conductor's resistance is determined by its material, the length over which the current runs, and the cross-sectional area through which it does so. Use the equation for a conductor's resistance.
A substance that carries electricity is called a conductor. This indicates that current can flow through it. Every conductor, though, makes it difficult for charges to pass through it and resists the flow of current. Resistance of the conductor is a word used to describe the conductor's oppositional nature.
A conductor's resistance is determined by its material, the length of current running through it, and the cross-sectional area through which it does so.
R=

ρ \frac{l}{A}

is the formula for a conductor's resistance, where l is its length, A is the cross-sectional area, and is the material's resistivity.
It is assumed that the conductor's length and cross sectional area have been doubled. The new length and cross sectional area are therefore 2l and 2A, respectively. Consequently, the conductor's new resistance is equal to R=

\frac{2 l}{2 A} = ρ \frac{l}{A}

. If we compare R and R', we can see that the conductor's resistance remains constant even after its length and cross-sectional area have both doubled.
Hence, option 2 is the correct answer.

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