Current Electricity Charging Discharging Of Capacitors Question 387
Question: A current I is passing through a wire having two sections P and Q of uniform diameters d and d/2 respectively. If the mean drift velocity of electrons in sections P and Q is denoted by vP and vQ respectively, then
[Roorkee 1999]
Options:
A) $ {v _{\text{P}}}={v _{\text{Q}}} $
B) $ {v _{\text{P}}}={v _{\text{Q}}} $
C) $ {v _{\text{P}}}=\frac{1}{4}{v _{\text{Q}}} $
D) $ {v _{\text{P}}}=\text{ 2}{v _{\text{Q}}} $
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Answer:
Correct Answer: C
Solution:
Drift velocity $ v _{d}=\frac{i}{neA}\Rightarrow v _{d}\propto \frac{1}{A}\text{ or},v _{d}\propto \frac{1}{d^{2}} $
$ \Rightarrow ,\frac{v _{P}}{v _{Q}}={{( \frac{d _{Q}}{d _{P}} )}^{2}}={{( \frac{d/2}{d} )}^{2}}=\frac{1}{4}\Rightarrow v _{P}=\frac{1}{4}v _{Q} $ .
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