# In pure semiconductor number of conducting electrons is $5 \times 10^{20}$ per cubic meter. How many holes are there in $1 cm^3$ of the same semiconductor.

$(a)\;5 \times 10^{14} \\ (b)\;5 \times 10^{-14} \\ (c)\;10^{-10} \\ (d)\;5 \times 10^{20}$

The number of conducting electrons in given sample
$\qquad= (volume \;of \;given \;sample) \times 5 \times 10^{20}$
$\qquad= 10^{-6} \times 5 \times 10^{20}$
$\qquad= 5 \times 10^{14}$
In pure semiconductor number of conducting electrons = number of holes.
Hence a is the correct answer.
answered Jan 27, 2014 by