A $$p$$-$$n$$ junction $$(D)$$ shown in the figure can act as a rectifier. An alternating current source $$(V)$$ is connected in the circuit.

The current $$(I)$$ in the resistor $$(R)$$ can be shown by :

A working transistor with its three legs marked $$P,Q$$ and $$R$$ is tested using a multi-meter. No conduction is found between $$P$$ and $$Q$$. By connecting the common (negative) terminal of the multi-meter to $$R$$ and the other (positive) terminal to $$P$$ or $$Q,$$ some resistance is seen on the multi-meter. Which of the following is true for the transistor?

In the circuit below, $$A$$ and $$B$$ represent two inputs and $$C$$ represents the output.

The circuit represents

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate ?