Semiconductors

A transistor is operated in common emitter configuration at $V_{\mathrm{C}}=2 \mathrm{V}$ such that a change in the base current from $100\mu \mathrm{A}$ to $300 \mu \mathrm{A}$ produces a change in the collector current from $10 \mathrm{mA}$ to $20 \mathrm{mA}$ . The current gain is

When a semiconductor is heated, its resistance-

In a semiconductor

The safety limit of temperatures for $\mathrm{Ge}$  and $\mathrm{Si}$  are-