If the ratio of the number density of electrons to the number density of holes in a semiconductor is $7/5$ and the ratio of their currents is $7/4$,what is the ratio of their drift velocities?

Which of the following statements is correct for an $n$-type semiconductor?

An intrinsic semiconductor is electrically neutral. What is the electrical state of an extrinsic semiconductor?

Which of the following when added as an impurity into silicon produces $n-$type semiconductor?

What is the conductivity of a semiconductor sample having electron concentration of $5 \times 10^{18} \, m^{-3}$,hole concentration of $5 \times 10^{19} \, m^{-3}$,electron mobility of $2.0 \, m^2 \, V^{-1} \, s^{-1}$,and hole mobility of $0.01 \, m^2 \, V^{-1} \, s^{-1}$? (Take charge of electron as $1.6 \times 10^{-19} \, C$)

Which of the following statements is incorrect?