Ask Questions, Get Answers

Want to ask us a question? Click here
Browse Questions
Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class12  >>  Current Electricity
0 votes

What is the average drift speed of conduction electrons in a copper wire of cross-sectional area $1.0 \times 10^{–7}m^2$ carrying a current of $1.5 A$. Assume that each copper atom contributes roughly one conduction electron. The density of copper is $ 9.0 \times 10^3 kg/m^3 $ , and its atomic mass is $ 63.5 u.$

$\begin {array} {1 1} (A)\;1.9mm/s & \quad (b)\;1.1 mm/s \\ (C)\;2.9 mm/s & \quad (D)\;2.2 mm/s \end {array}$


Can you answer this question?

1 Answer

0 votes
The direction of drift velocity of conduction electrons is opposite to the electric field direction,
i.e., electrons drift in the direction of increasing potential. The drift speed$v_d$ is given by
$ v_d =( I / neA)$
Now $ e=1.6 \times 10^{-19}C,A= 1.0 \times 10^{-7}m^2, I =1.5A$
The density of conduction electrons, $n$ is equal to the number of atoms per cubic meter
(assuming one conduction electron per $ Cu$ atom as is reasonable from its valence electron count of one).
A cubic meter of copper has a mass of $9.0 \times 10^3 \: kg$. Since $6.0 \times 10^{23}$ copper atoms have a mass of $ 63.5 g,$
$ n = \large\frac{6 \times 10^{23}}{63.5}$ $ \times 9 \times 10^{6} = 8.5 \times 10^{28}$
on substituting in the formula for$v_d$, one gets the final answer as $1.1 mm/s$
Ans : (B)


answered Feb 14, 2014 by thanvigandhi_1
edited Sep 4, 2014 by thagee.vedartham

Related questions

Ask Question
student study plans
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App