The density of electron-hole pair in a pure germanium is $3 \times 10^{16} \mathrm{~m}^{-3}$ at room temperature. On doping with aluminium, the hole density increases to $4.5 \times 10^{22} \mathrm{~m}^{-3}$. Now, the electron density (in $\mathrm{m}^{-3}$ ) in doped germanium will be

The DC common emitter current gain of an $n-p-n$ transistor is 50 . The potential difference applied across the collector and emitter of a transistor used in CE configuration is, $V_{C E}=2 \mathrm{~V}$. If the collector resistance $R_C=4 \mathrm{k} \Omega$, the base current $\left(I_B\right)$ and the collector current $\left(I_C\right)$ are

In the three parts of a transistor, 'Emitter' is of

The energy gap in case of which of the following is less than 3 eV ?