A current of 1.8 A flows through a wire of cross-section 0.5 mm$^2$...

Question

A current of 1.8 A flows through a wire of cross-section 0.5 mm$^2$. Find: (a) current density, (b) drift velocity. (Number density $n = 8.8 	imes 10^{28}$ m$^{-3}$)

Accepted Answer

(a) $A = 0.5 	imes 10^{-6}$ m$^2$
$$J = \frac{I}{A} = \frac{1.8}{0.5 	imes 10^{-6}} = 3.6 	imes 10^6 	ext{ A/m}^2$$

(b)
$$v_d = \frac{J}{ne} = \frac{3.6 	imes 10^6}{8.8 	imes 10^{28} 	imes 1.6 	imes 10^{-19}} = \frac{3.6 	imes 10^6}{1.408 	imes 10^{10}} \approx 2.56 	imes 10^{-4} 	ext{ m/s}$$

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