Ohm's law may be expressed as

$1.\square Potentialdifference,V\propto I(electriccurrent)\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}2.\square Electriccurrentdensity,j\propto E(electricfield)\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}3.\square \frac{V}{I}=\rho \frac{l}{A},symbolshavingusualmeaning\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}4.\square Resis\mathrm{tan}ce,R=\frac{V}{I}=cons\mathrm{tan}t$

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