QJEEM18Ph8d3b: JEE Main 2018 Physics - Class 12 JEEM18Ph8d3b Solution: A copper rod of cross-sectional area A carries a uniform…

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A copper rod of cross-sectional area A carries a uniform current I through it. At temperature T, if the volume charge density of the rod is

ρ

, how long will the changes take to travel a distance d ?

Accepted Answer

Given : Volume charge density of rod = $ρ$ .

We know that current $I = n e A v_{d}$ ; where n is number of electrons, e is electronic charge, A is area, v_d is drift velocity

JEE Main 2018 (Online) 15th April Evening Slot Physics - Current Electricity Question 287 English Explanation

Since volume charge density is $ρ$ = ne. Therefore,

$I = ρ A v_{d} \Rightarrow v_{d} = \frac{I}{ρ_{A}}$

Now, time = $\frac{d i s \tan c e}{s p e e d}$

$\Rightarrow$ time $= \frac{d}{v_{d}} = \frac{d}{I / ρ A} = \frac{ρ A d}{I}$

Thus, time required to travel distance $d = \frac{ρ d A}{I}$

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