If the ratio of the concentration of electrons to that of holes in a semiconductor is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4}$,then what is the ratio of their drift velocities?

$A$ semiconductor has equal electron and hole concentration of $2 \times 10^8 \ m^{-3}$. On doping with a certain impurity, the electron concentration increases to $4 \times 10^{10} \ m^{-3}$. What is the new hole concentration of the semiconductor?

$A$ donor impurity results in

$A$ pure $Si$ crystal has $5 \times 10^{28}$ atoms $m^{-3}$. It is doped with $1 \, ppm$ concentration of pentavalent $As$. The number of holes is (Take $n_i = 1.5 \times 10^{16} \, m^{-3}$)

$A$ semiconductor has equal electron and hole concentration of $6 \times 10^8 \, m^{-3}$. On doping with a certain impurity,the electron concentration increases to $9 \times 10^{12} \, m^{-3}$. The new hole concentration is:

In an intrinsic semiconductor at room temperature, the number of electrons and holes are: