Four logic gates are connected as shown in the figure. If the inputs are $A=0, B=1$ and $C=1$, then the values of $Y_1$ and $Y_2$ respectively, are

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