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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? - Physics

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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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Experimental Study of Photoelectric Effect
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पाठ 20: Photoelectric Effect and Wave-Particle Duality - Short Answers [पृष्ठ ३६३]

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एचसी वर्मा Concepts of Physics Vol. 2 [English] Class 11 and 12
पाठ 20 Photoelectric Effect and Wave-Particle Duality
Short Answers | Q 8 | पृष्ठ ३६३

संबंधित प्रश्‍न

(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?


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.


Light of wavelength λ falls on a metal with work-function hc/λ0. Photoelectric effect will take place only if


Calculate the number of photons emitted per second by a 10 W sodium vapour lamp. Assume that 60% of the consumed energy is converted into light. Wavelength of sodium light = 590 nm

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


A beam of white light is incident normally on a plane surface absorbing 70% of the light and reflecting the rest. If the incident beam carries 10 W of power, find the force exerted by it on the surface.

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


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, find the force exerted by the light beam on the sphere.

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


Show that it is not possible for a photon to be completely absorbed by a free electron.


The work function of a metal is 2.5 × 10−19 J. (a) Find the threshold frequency for photoelectric emission. (b) If the metal is exposed to a light beam of frequency 6.0 × 1014 Hz, what will be the stopping potential?

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


Find the maximum magnitude of the linear momentum of a photoelectron emitted when a wavelength of 400 nm falls on a metal with work function 2.5 eV.

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


The electric field associated with a monochromatic beam is 1.2 × 1015 times per second. Find the maximum kinetic energy of the photoelectrons when this light falls on a metal surface whose work function is 2.0 eV.

(Use h = 6.63 × 10-34J-s = 4.14 × 10-15 eV-s, c = 3 × 108 m/s and me = 9.1 × 10-31kg)


Define the term: threshold frequency


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?


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.

Why it is the frequency and not the intensity of the light source that determines whether the emission of photoelectrons will occur or not? Explain.


If photons of ultraviolet light of energy 12 eV are incident on a metal surface of work function of 4 eV, then the stopping potential (in eV) will be :


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


Plot a graph showing the variation of photoelectric current, as a function of anode potential for two light beams having the same frequency but different intensities I1 and I2 (I1 > I2). Mention its important features.


What is the effect of threshold frequency and stopping potential on increasing the frequency of the incident beam of light? Justify your answer.


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