Gujarat BoardEnglish MediumSTD 12 ScienceChemistryElectrochemistry2 Marks
Question
What is the electric resistance and resistivity ?
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Answer
→ "The electrical resistance of any object is directly proportional to its length. 1, and inversely proportional to its area of cross section, A." $\begin{array}{l}→ R \propto \frac{l}{A} \\ \therefore R =\rho \cdot \frac{l}{A}\end{array}$ Where, $\rho=$ Resistivity (Or) specfic resistance → The electrical resistance is represented by the symbol 'R' and it is measured in ohm $(\Omega)$ → SI unit is $kgm ^2 / s ^3 \cdot A ^2$ → It can be measured with the help of awheatstone bridge. → "The resistivity for a substance is its resistance when it is one metre long and its area of cross section is one $m^2$." $ \therefore \rho= R \left(\frac{ A }{l}\right) $ → Its SI units are ohm metre $(\Omega M )$ and quite often its submultiple. ohm centimetre ( $\Omega$ $cm$ ) is also used. $1 \Omega\ m =100 \ \ \Omega \ cm$ or $1 \Omega \ cm =0.01 \ \Omega \ m$
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