In n-type semiconductor, free electrons donated by the impurity atoms occupy energy levels in

In a pure silicon crystal electron-hole concentration is $10^{16}$ per $\mathrm{m}^3$ at 301 K . Now $10^{21}$ atoms of phosphorus are added per cubic metre. The new hole concentration in silicon is (in per $\mathrm{m}^3$ )

In a common emitter transistor amplifier, the output voltage and input voltage have a phase difference of

If a centre tap transformer is used with two p-n junction diodes for full wave rectification then output voltage of rectifier with respect to each diode is (secondary voltage of transformer $=\mathrm{V}_{\mathrm{s}}$ )