First slide

Ohm's law

Question

A certain piece of copper is to be shaped into a conductor of minimum resistance. Its length and diameter should be respectively

Moderate

A

I,d
B

2l,d
C

$\frac{l}{2}, 2 d$
D

$2 l, \frac{d}{2}$

Solution

We know that
$\begin{array}{l} R = ρ \frac{l}{{πr}^{2}} or R = 4 ρ \frac{l}{{πd}^{2}} \\ ∴ R \propto \frac{l}{d^{2}} \end{array}$
For minimum resistance l should be smallest and d should be largest

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