51.

To which logic gate does the truth table given below correspond?

           

• AND

• OR

• NAND

• XOR

Avalanche breakdown in a p-n junction diode is due to

• shift of fermi level

• widening of forbidden gap

• high impurity concentration

• cummulative effect of conduction band electrons collision

If the radius of the first Bohr orbit of the hydrogen atom is 5.29 x 10' m, the radius of the second orbit will be

• 21.16 x 10⁻¹¹ m

• 15.87 x 10⁻¹¹  m

• 10.58 x 10⁻¹¹ m

• 2.64 x 10⁻¹¹  m

Number of nuclei of a radioactive substance at time t = O are 2000 and 1800 at time t = 2s. Number of nuclei left after t = 6s is

• 1442

• 1554

• 1652

• 1458

₉₂U²³⁸ on absorbing a neutron goes over to ₉₂U²³⁹. This nucleus emits an electron to go over to neptunium which on further emitting an electron goes over to plutonium. The resulting plutonium can be expressed as

• ₉₄Pu²³⁹

• ₉₀Pu²¹⁹

• ₉₃Pu²⁴⁰

• ₉₂Pu²⁴⁰

The energy of a photon corresponding to the visible light of maximum wavelength is approximately

• 1 eV

• 1.6 eV

• 3.2 eV

• 7 eV

If the binding energy of the electron in a hydrogen atom is 13.6 eV, the energy required to remove the electron from the first excited state of Li²⁺ is

• 30.6 eV

• 13.6 eV

• 3.4 eV

• 122.4 eV

To demonstrate the phenomenon of interference we require two sources which emit radiations of

• nearly the same frequency

• the same frequency

• different wavelengths

• the same frequency and having a definite phase relationship

To get three images of a single object, one should have two plane mirrors at an angle of

• 60°

• 90°

• 120°

• 30°

Consider telecommunication through optical fibres. Which of the following statements is not true?

• Optical fibres can be of graded refractive index

• Optical fibres are subjected to electromagnetic interference from outside

• Optical fibres have extremely low transmission loss

• Optical fibres may have homogeneous core with a suitable cladding