A $p-n$ junction is fabricated from a semiconductor with band gap of 2.8 eV . what approximate wavelength it cannot detect? [Use, $h=6 \times 10^{-34} \mathrm{~m}^2 \mathrm{~kg} / \mathrm{s}$ ]

Identify the logic operation performed by the following circuit.

The number of silicon atoms per $\mathrm{m}^3$ is $5 \times 10^{28}$. This is doped with $4.5 \times 10^{21}$ atoms $/ \mathrm{m}^3$ of arsenic. The ratio of number of electrons to number of holes after doping is (take $n_i=$ number of thermally generated electrons $=1.5 \times 10^{16} / \mathrm{m}^3$ )

The output of the following circuit is equivalent to $.......$ gate