Question

The drift velocity of the electrons in a copper wire of length $ 2 \,m $ under the application of a potential difference of $ 220\, V $ is $ 0.5\text{ }m{{s}^{-1}} $ . Their mobility (in $ {{m}^{2}}{{V}^{-1}}{{s}^{-1}} $ )

• A. $ 2.5\times {{10}^{-3}} $
• B. $ 2.5\times {{10}^{-2}} $
• C. $ 5\times {{10}^{2}} $
• D. $ 5\times {{10}^{-3}} $
• E. $ 5\times {{10}^{-2}} $

Answer 1

Answer: (D)

Drift velocity = mobility x intensity of electric field or
$ {{v}_{d}}=\mu E $ or $ \mu =\frac{{{v}_{d}}}{E} $
or $ \mu =\frac{{{v}_{d}}}{V/l} $
$ \left( \because E=\frac{V}{l} \right) $
$ \therefore $ $ \mu =\frac{0.5\times 2}{220}=4.5\times {{10}^{-3}} $
$ \approx 5\times {{10}^{-3}}{{m}^{2}}{{V}^{-1}}{{s}^{-1}} $