Question

How did resistivity change from rho=RA/l to Rπd^/4l
Please someone explain​

Answer 1

Hii da.. Here is ur explanation:

The first equality is a general derivation of resistivity and ‘A' is general symbol for areaSo,. The second formula is specific to a conductor of common circular cross section in which 'A' is replaced by πr^2 or π(d/2)^2 . Square(2) in d^2 is missing in your question. Substitute as above in second equality ..You'll get d ans!!

How did resistivity change from rho=RA/l to Rπd^/4l?

There is no change to the resistivity equation. The second expression relates specifically to a conductor with a circular cross section.

In this type of conductor:

Cross sectional area A = (pi * d^2) / 4

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Answer 2

Resistivity, electrical resistance of a conductor of unit cross-sectional area and unit length. A characteristic property of each material, resistivity is useful in comparing various materials on the basis of their ability to conduct electric currents. High resistivity designates poor conductors..........

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