Pure silicon at 300 K has equal electron and hole concentration of $1.5 \times 10^{16} \mathrm{~m}^{-3}$. If the hole concentration increases to $3 \times 10^{22} \mathrm{~m}^{-3}$, then electron concentration in the silicon is

In $n-p-n$ transistor circuit, the collector current is 10 mA . If $95 \%$ of the electrons emitted reach the collector, then the base current is nearly

The semiconductor used for fabrication of visible LEDS must at least have a band gap of

In a common emitter amplifier, AC current gains 40 and input resistance is $2 \mathrm{k} \Omega$. The load resistance is given as $10 \mathrm{k} \Omega$. Then, the voltage gain is