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WAEC Physics 2011 Paper

Question : 40

Total: 49

\mathit{P}

Solution:

Concept:

Resistivity links resistance to the dimensions of a conductor.

Explanation:

The resistance

R

of a wire is directly proportional to its length

l

and inversely proportional to its cross-sectional area

A

Hence,

R = \frac{P l}{A}

, where

P

is the resistivity.

Rearranging this formula to make

P

the subject gives

P = \frac{RA}{l}

Answer:

Option A.

\mathit{P} = \frac{RA}{l}

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