51.

The variation of photocurrent with collector potential for different frequencies of incident radiation v₁, v₂ and v₃ is as shown in the graph, then

           

• v₁ = v₂ = v₃

• v₁ > v₂ > v₃

• v₁ < v₂ < v₃

• ${\mathrm{v}}_3 = \frac{{\mathrm{v}}_1 + {\mathrm{v}}_2}{2}$

The de-Broglie wavelength of an electron accelerated to a potential of 400 V is approximately

• 0.03 nm

• 0.04 nm

• 0.12 nm

• 0.06 nm

Total energy of electron in an excited state of hydrogen atom is − 3.4 eV. The kinetic and potential energy of electron in this state are

• K = − 3.4 eV, U = − 6.8 eV

• K = 3.4 eV, U − 6.8 eV

• K = − 6.8 eV, U = + 3.4 eV

• K = + 10.2 eV, U = − 13.6 eV

When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by

• $\frac{\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{2\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{3\mathrm{h}}{2\mathrm{\pi }}$

• $\frac{4\mathrm{h}}{2\mathrm{\pi }}$

A radioactive sample of half-life 10 days contains 1000 x nuclei. Number of original nuclei present after 5 days is

• 707 x

• 750 x

• 500 x

• 250 x

An element X decays into element Z by two-step process

                      $$\begin{gathered} \mathrm{X} \stackrel{}{\to } \mathrm{Y} + {}_2{}^4\mathrm{He} \\ \mathrm{Y} \stackrel{}{\to } \mathrm{Z} + 2{\mathrm{e}}^{-}, \mathrm{then} \end{gathered}$$

• X and Z are isobars

• X and Y are isotopes

• X and Z are isotones

• X and Z are isotopes

A nucleus of mass 20 u emits a γ-photon of energy 6 MeV. If the emission assume to occur when nucleus is free and rest, then the nucleus will have kinetic energy nearest to (Take, 1 u = 1.6 × 10^-27 kg)

• 10 keV

• 1 keV

• 0.1 keV

• 100 keV

Constant DC voltage is required from a variable AC voltage. Which of the following is correct order of operation ?

• Regulator, filter, rectifier

• Rectifier, regulator, filter

• Rectifier, filter, regulator

• Filter, regulator, rectifier

In a transistor, the collector current varies by 0.49 mA and emitter current varies by 0.50 mA. Current gain β measured is

• 49

• 150

• 99

• 100

Identify the logic operation carried out by the following circuit

• AND

• NAND

• NOR

• OR