A pure silicon crystal at temperature $300$ K has electron and hole concentration ($n_i$) $10^{16}$ per m$^3$ each and $10^{21}$ phosphorus atoms ($n_e$) are added per cubic metre. The new hole concentration in silicon crystal is

If transistor having $\alpha = 0.9$, is used in CE configuration, then for a change of $0.4$ mA in base current, what will be the change in collector current?

Choose the correct statement about Zener diode:

In common emitter mode of transistor, the d.c. current gain is 20, the emitter current is 7 mA. The collector current is