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Physics Question on Current electricity

A conductor wire having 102910^{29} free electrons/m3m^{3} carries a current of 20 A20\,A. If the cross-section of the wire is 1 mm21\,mm^{2}, then the drift velocity of electrons will be ....... (e = 1.6×10−19C).(e\, =\, 1.6 \times10^{-19}C).

A

12.5×10−3ms−112.5 \times 10^{-3} ms^{-1}

B

1.25×10−4ms−11.25 \times 10^{-4} ms^{-1}

C

1.25×10−5ms−11.25 \times 10^{-5} ms^{-1}

D

1.25×10−3ms−11.25 \times10^{-3} ms^{-1}

Answer

1.25×10−4ms−11.25 \times 10^{-4} ms^{-1}

Explanation

Solution

Current, I=nAevdI=nAev _{d}
∴\therefore Drift velocity vd=InAev_{d}=\frac{I}{n A e}
=201029×10−6×1.6×10−19=\frac{20}{10^{29} \times 10^{-6} \times 1.6 \times 10^{-19}}
vd=1.25×10−3 ms−1v_{d} =1.25 \times 10^{-3}\, ms ^{-1}