The image formed by an objective of a compound microscope is

A strip of copper and another of germanium are cooled from room temperature to $$80K.$$ The resistance of

The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the

Three charges $$ - {q_1}, + {q_2}$$ and $$ - {q_3}$$ are placed as shown in the figure. The $$x$$-component of the force on $$ - {q_1}$$ is proportional to