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It is Found that Yellow Light Does Not Eject Photoelectrons from a Metal. is It Advisable to Try with Orange Light Or with Green Light?

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प्रश्न

It is found that yellow light does not eject photoelectrons from a metal. Is it advisable to try with orange light or with green light?

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उत्तर

Photoelectrons are emitted from a metal's surface if the frequency of incident radiation is more than the threshold frequency of the given metal surface. As yellow light does not eject photoelectrons from a metal it means that the threshold frequency of the metal is more than the frequency of yellow light. Since the frequency of orange light is less than the frequency of yellow light, therefore it will not be able to eject photoelectrons from the metal's surface. The frequency of green light is more than the frequency of yellow light. Hence, when it is incident on the metal surface, it will eject electrons from the metal.

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पाठ 42: Photoelectric Effect and Wave-Particle Duality - Short Answers [पृष्ठ ३६३]

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एचसी वर्मा Concepts of Physics Volume 1 and 2 [English]
पाठ 42 Photoelectric Effect and Wave-Particle Duality
Short Answers | Q 8 | पृष्ठ ३६३

संबंधित प्रश्‍न

The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy of photoelectrons emitted?


(a) Estimate the speed with which electrons emitted from a heated emitter of an evacuated tube impinge on the collector maintained at a potential difference of 500 V with respect to the emitter. Ignore the small initial speeds of the electrons. The specific charge of the electron, i.e., its e/m is given to be 1.76 × 1011 C kg−1.

(b) Use the same formula you employ in (a) to obtain electron speed for an collector potential of 10 MV. Do you see what is wrong? In what way is the formula to be modified?


Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?


Draw graphs showing variation of photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.


Can we find the mass of a photon by the definition p = mv?


Is it always true that for two sources of equal intensity, the number of photons emitted in a given time are equal?


It is found that photosynthesis starts in certain plants when exposed to sunlight, but it does not start if the plants are exposed only to infrared light. Explain.


The threshold wavelength of a metal is λ0. Light of wavelength slightly less than λ0 is incident on an insulated plate made of this metal. It is found that photoelectrons are emitted for some time and after that the emission stops. Explain.


Two photons of 


The work function of a metal is hv0. Light of frequency v falls on this metal. Photoelectric effect will take place only if


A sphere of radius 1.00 cm is placed in the path of a parallel beam of light of large aperture. The intensity of the light is 0.5 W cm−2. If the sphere completely absorbs the radiation falling on it, Show that the force on the sphere due to the light falling on it is the same even if the sphere is not perfectly absorbing.


The figure is the plot of stopping potential versus the frequency of the light used in an experiment on photoelectric effect. Find (a) the ratio h/e and (b) the work function.


Define the terms "stopping potential' and 'threshold frequency' in relation to the photoelectric effect. How does one determine these physical quantities using Einstein's equation?


Explain how does (i) photoelectric current and (ii) kinetic energy of the photoelectrons emitted in a photocell vary if the frequency of incident radiation is doubled, but keeping the intensity same?

Show the graphical variation in the above two cases.


In photoelectric effect, the photoelectric current started to flow. This means that the frequency of incident radiations is ______.


Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. Find the work function in eV.


Consider a 20 W bulb emitting light of wavelength 5000 Å and shining on a metal surface kept at a distance 2 m. Assume that the metal surface has work function of 2 eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 Å.

  1. Estimate no. of photons emitted by the bulb per second. [Assume no other losses]
  2. Will there be photoelectric emission?
  3. How much time would be required by the atomic disk to receive energy equal to work function (2 eV)?
  4. How many photons would atomic disk receive within time duration calculated in (iii) above?
  5. Can you explain how photoelectric effect was observed instantaneously?

The graph shows the variation of photocurrent for a photosensitive metal

  1. What does X and A on the horizontal axis represent?
  2. Draw this graph for three different values of frequencies of incident radiation ʋ1, ʋ2 and ʋ33 > ʋ2 > ʋ1) for the same intensity.
  3. Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I3 > I2 > I1) having the same frequency.

How would the stopping potential for a given photosensitive surface change if the intensity of incident radiation was decreased? Justify your answer.


How would the stopping potential for a given photosensitive surface change if the frequency of the incident radiation were increased? Justify your answer.


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