Light of wavelength 500 nm is incident on metal with work functi

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 Multiple Choice QuestionsMultiple Choice Questions

71.

Light with an energy flux of 25 x 104 W/m2 falls on a perfectly reflecting surfaces at normal incidence. If the surface area is 15 cm2, the average force exerted on the surface is,

  • 1.25 x 10-6 N

  • 2.50 x 10-6 N

  • 1.20 x 10-6 N

  • 1.20 x 10-6 N

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72.

When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is,

  • 0.65 eV

  • 1.0 eV

  • 1.3 eV

  • 1.3 eV

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73.

If the kinetic energy of the particle is increased to 16 times its previous value, the percentage change in the de-Broglie wavelength of the particle is,

  • 25

  • 75

  • 60

  • 60

767 Views

74.

For photoelectric emission from certain metal, the cut-off frequency is v. If radiation of frequency is v. If radiation of frequency 2v impinges on the metal plate, the maximum possible velocity of the emitted electrons will be (m is the electron mass)

  • square root of fraction numerator hv over denominator left parenthesis 2 straight m right parenthesis end fraction end root
  • square root of hv over straight m end root
  • square root of fraction numerator 2 hv over denominator straight m end fraction end root
  • square root of fraction numerator 2 hv over denominator straight m end fraction end root
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75.

In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

  • Increasing the filament current

  • decreasing the filament current

  • decreasing the potential difference between the anode and filament

  • decreasing the potential difference between the anode and filament

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76.

In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding  stopping potential is

  • 1.3 V

  • 0.5 V

  • 2.3 V 

  • 2.3 V 

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77.

Photoelectric emission occurs only when the incident light has more than a certain minimum

  • wavelength

  • intensity

  • frequency

  • frequency

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78.

A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is 

(h = planck's constant, c= speed of light)

  • hc/ 2λ

  • hc/λ

  • 2 hc/λ

  • 2 hc/λ

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79.

Light of wavelength 500 nm is incident on metal with work function 2.28 eV. The de - Broglie wavelength of the emitted electrons is 

  • <2.8 x 10-10

  • <2.8 x 10-9 m

  • > equal  to 2.8 x 10-9 m

  • > equal  to 2.8 x 10-9 m


B.

<2.8 x 10-9 m

As, energy of photon, E = hv

straight E space space equals space hc over straight lambda
rightwards double arrow space straight E space equals space fraction numerator 6.626 space straight x space 10 to the power of negative 34 end exponent space straight x space 3 space straight x space 10 to the power of 8 over denominator 500 space straight x space 10 to the power of negative 9 end exponent end fraction
rightwards double arrow space straight E space equals space fraction numerator 0.0397 space straight x space 10 to the power of negative 34 end exponent space straight x space 10 to the power of 8 over denominator 10 to the power of negative 9 end exponent end fraction space equals space 0.0397 space straight x space 10 to the power of negative 21 end exponent space straight J
equals space fraction numerator 0.0397 space straight x space 10 to the power of negative 21 end exponent over denominator 1.6 space straight x space 10 to the power of negative 19 end exponent end fraction space equals space 0.0248 space straight x space 10 squared space eV
space equals space 2.48 space eV
According space to space Einstein apostrophe straight s space photoelectric space emission comma space
we space have
KE subscript max space equals space straight E space minus space straight W space equals space 2.48 space minus space 2.28 space equals space 0.2 space eV
For space de space minus space broglie space wavelength space of space the space emitted space electron comma

straight lambda subscript straight e space min end subscript space equals space fraction numerator 12.27 over denominator square root of KE subscript max space eV end root end fraction space equals space fraction numerator 12.27 over denominator square root of 0.2 end root end fraction

equals space 27.436 space straight A with straight o on top space space equals 27.436 space straight x space 10 to the power of negative 10 end exponent straight m
Thus comma space minimum space wavelength space space of space the space emitted space electron space is
straight lambda subscript min space equals space 2.7436 space straight x 10 to the power of negative 9 end exponent space straight m space
straight lambda greater or equal than space straight lambda subscript min

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80.

The threshold frequency for a photo-sensitive metal is 3.3 x 1014 Hz. If light of frequency 8.2 x 1014 Hz is incident on this metal, the cut -off voltage for the photo-electric emission is nearly

  • 2 V

  • 3 V

  • 5 V

  • 5 V

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