A radiation of energy 'E' falls normally on a perfectly reflecti

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 Multiple Choice QuestionsMultiple Choice Questions

61.

A caesium photocell, with a steady potential difference of 60 V across it, is illuminated by a bright point source of light 50 cm away. When the same light is placed 1 cm away, the photoelectrons emitted from the cell

  • are half as numerous

  • are one quarter as numerous

  • each carry one quarter of their previous energy

  • each carry one quarter of their


62.

When a metallic surface is illuminated with radiation of wavelength straight lambda, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2 straight lambda, the stopping potential is V/4. The threshold wavelength for the metallic surface is,

  • 5 straight lambda
  • 5 over 2 lambda
  • 3straight lambda

  • 3straight lambda

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63.

A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U1, at wavelength 500 nm is U2 and that at 1000 nm is U3. Wien's constant, b = 2.88 x 106 nmK. Which of the following is correct?

  • U3 = 0

  • U1 > U2

  • U2 > U1

  • U2 > U1

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64.

A radiation of energy 'E' falls normally on a perfectly reflecting surface. The momentum transferred to the surface is 
(c = velocity of light)

  • straight E over straight c
  • fraction numerator 2 straight E over denominator straight c end fraction
  • fraction numerator 2 straight E over denominator straight c squared end fraction
  • fraction numerator 2 straight E over denominator straight c squared end fraction


B.

fraction numerator 2 straight E over denominator straight c end fraction

The radiation energy is given by 

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65.

An electron of mass m and a photon have the same energy E. The ratio of de-Broglie wavelength associated with them is,

  • open parentheses fraction numerator straight E over denominator 2 straight m end fraction close parentheses to the power of begin inline style bevelled 1 half end style end exponent
  • straight c space left parenthesis 2 mE right parenthesis to the power of begin inline style bevelled 1 half end style end exponent
  • 1 over straight c open parentheses fraction numerator 2 m over denominator E end fraction close parentheses to the power of begin inline style bevelled 1 half end style end exponent
  • 1 over straight c open parentheses fraction numerator 2 m over denominator E end fraction close parentheses to the power of begin inline style bevelled 1 half end style end exponent
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66.

Which of the following figures represent the variation of particle momentum and the associated de-Broglie wavelength?

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67.

If the momentum of an electron is chagned by p, then the de-Broglie wavelenght associated with it changes by 0.5%. The initial momentum of electron will be

  • 200p

  • 400p

  • p/200

  • p/200

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68.

Two radiations of photon energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of the maximum speeds of the emitted electrons is

  • 1:4

  • 1:2

  • 1:1

  • 1:1

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69.

An α- particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m2. The de-Broglie wavelength associated with the particle will be

  • 1 Ao

  • 0.1 Ao

  • 10 Ao

  • 10 Ao

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70.

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

  • 4 x 1015 Hz

  • 5 x 1015 Hz

  • 1.6 x1015 Hz

  • 1.6 x1015 Hz

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