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

The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by

A particle performing uniform circular motion has angular frequency is doubled & its kinetic energy halved, then the new angular momentum is