An electron is revolving in a circular orbit of radius 'r' in hydrogen atom. Using Bohr's theory, the angular momentum of the electron is
(M = magnetic dipole moment, m = mass of electron)

Which of the following graph represents the temperature (T) dependence of resistivity ($\rho$) of a semiconductor?

In common emitter mode of transistor, the d.c. current gain is 20, the emitter current is 7 mA. The collector current is

In transistor amplifier, base emitter junction is forward biased and collector base junction is reversed biased. The current gain is