To use a transistor as an amplifier,which of the following conditions must be satisfied?

$A$ transistor is connected in a common emitter configuration with $R_o = 4 \text{ k}\Omega$,$R_i = 1 \text{ k}\Omega$,$I_C = 1 \text{ mA}$,and $I_b = 20 \text{ }\mu\text{A}$. The voltage gain is:

In an $n-p-n$ transistor circuit,the collector current is $10 \, mA$. If $90 \%$ of the electrons reach the collector,then the emitter current will be:

The transfer characteristics [output voltage $(V_o)$ vs input voltage $(V_i)$] for a base-biased transistor in $CE$ configuration are shown in the figure. For using a transistor as a switch,it is used:

$A$ transistor is used in common-emitter mode in an amplifier circuit. When a signal of $10 \, mV$ is added to the base-emitter voltage, the base current changes by $10 \, \mu A$ and the collector current changes by $1.5 \, mA$. The load resistance is $5 \, k\Omega$. The voltage gain of the transistor will be

The transistors provide good power amplification when they are used in