51.

The ground state energy of H-atom is 13.6 eV. The energy needed to ionize H-atom from its second excited state is

• 1.51 eV

• 3.4 eV

• 13.6 eV

• 12.1 eV

Forward bias characteristics of a p-n junction diode are used in which of the following devices?

• Transistor

• Tank circuit

• Rectifier

• All of these

The energy gap between the conduction band and valence band is of the order of 0.07 eV. It is a/an

• insulator

• conductor

• semiconductor

• alloy

An oscillator is basically an amplifier with gain

• less than unity

• more than unity

• zero

• 0.5

A particle of mass m at rest decays into two particles of masses m₁ and m₂ having non zero velocities. The ratio of de-Broglie wavelengths of the particles $\frac{{\mathrm{\lambda }}_1}{{\mathrm{\lambda }}_2}$ is

• m₁/m₂

• m₂/m₁

• 1.0

• $\sqrt{\frac{{\mathrm{m}}_2}{{\mathrm{m}}_1}}$

A triode valve has an amplification factor of 20 and its plate is given a potential of 300 V. The grid voltage to reduce the plate current to zero, is

• 25 V

• 12 V

• 10 V

Which one of the following does not support the wave nature of light?

• Photoelectric effect

• Interference

• Polarization

• Diffraction

Which of the following nuclei is fissionable but not possible?

• ${}_{92}\mathrm{U}^{235}$

• ${}_{92}\mathrm{U}^{233}$

• ${}_{92}\mathrm{U}^{238}$

• ${}_{94}\mathrm{Pu}^{239}$

In a common base amplifier, the phase difference between the input signal voltage and the output voltage is

• $\frac{\mathrm{\pi }}{4}$

• $\mathrm{\pi }$

• zero

• $\frac{\mathrm{\pi }}{2}$