A cylindrical metal rod has a resistance . If both its length and its diameter are quadrupled, its new resistance will be:. A. 16R
B. R/4
C. R
D. 4R

R' = R/4

Explanation:

The resistance of a metal rod is R. It is given by the relation as follows :

Where

l is the length and A is the area of cross-section

If both its length and its diameter are quadrupled, it means,

l' = 4l

and d'= 4d

It means,

Let new resistance be R'. So,

So, the correct option is (B) "R/4".

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