A realistic graph depicting the variation of the reciprocal of input resistance in an input characteristics measurement in a common emitter transistor configuration is :

A signal of $5 \mathrm{kHz}$ frequency is amplitude modulated on a carrier wave of frequency $2 \mathrm{MHz}$. The frequencies of the resultant signal is/are:

The value of the resistor, $R_S$, needed in the DC voltage regulator circuit shown here, equals:

Given, $A$ and $B$ are input terminals

Logic $1$ is$>5 \mathrm{V}$

Logic $0$ is$<1 \mathrm{V}$

Which logic gate operation, the following circuit does?

Note: This question was awarded a bonus. $C$ option changed. 

An n-p-n transistor has three leads A, B and C. Connecting B and C by moist fingers, A to the positive lead of an ammeter, and C to the negative lead of the ammeter, one finds large deflection. Then, A, B and C refer respectively to :

A transmitting antenna at the top of a tower has a height $32 \mathrm{m}$ and the height of the receiving antenna is $50 \mathrm{m}$. What is the maximum distance between them for satisfactory communication in line of sight (LOS) mode?