The number of free electrons per 100 mm of ordinary copper wire is 2 × 1021 . Average drift speed of electrons is 0.25 mm/s . The current flowing is :

Question

The number of free electrons per 100 mm of ordinary copper wire is 2 × 1021 . Average drift speed of electrons is 0.25 mm/s . The current flowing is : (A)  5 A  (B)  80 A  (C)  8 A  (D)  0.8 A

Tardigrade Admin · Accepted Answer

Drift velocity is defined as the average velocity that a particle attains due to an electric field.

v_{d} = \frac{i}{n e A}

where

i

is current,

n

the number of electrons,

e

the electron charge and

A

the area of crosssection of wire.
Number of electrons per unit volume

n = \frac{2 \times 1 0 ^{21}}{A \times 100}

Hence, current in the wire

i = n e A v_{d}

i = \frac{2 \times 1 0 ^{21}}{A \times 100} \times 1.6 \times 1 0^{- 19} \times A \times 0.25

i = 0.8 A

Q. The number of free electrons per $100 mm$ of ordinary copper wire is $2 \times 1 0^{21}$ . Average drift speed of electrons is $0.25 mm / s$ . The current flowing is :

$5 A$

$80 A$

$8 A$

$0.8 A$

Q. The number of free electrons per 100mm of ordinary copper wire is 2×1021 . Average drift speed of electrons is 0.25mm/s . The current flowing is :

5A

80A

8A

0.8A

Q. The number of free electrons per $100 mm$ of ordinary copper wire is $2 \times 1 0^{21}$ . Average drift speed of electrons is $0.25 mm / s$ . The current flowing is :

$5 A$

$80 A$

$8 A$

$0.8 A$