English
Karnataka Board PUCPUC Science Class 11

The Work Function of a Metal is Hv0. Light of Frequency V Falls on this Metal. Photoelectric Effect Will Take Place Only If

Advertisements
Advertisements

Question

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

Options

  • v ≥ v0

  • v > 2v0

  • v < v0

  • v < v0/2

MCQ
Advertisements

Solution

v ≥ v0

As the work function of the metal is hv0, the threshold frequency of the metal is v0.

For photoelectric effect to occur, the frequency of the incident light should be greater than or equal to the threshlod frequency of the metal on which light is incident.

shaalaa.com
  Is there an error in this question or solution?
Chapter 42: Photoelectric Effect and Wave-Particle Duality - MCQ [Page 363]

APPEARS IN

HC Verma Concepts of Physics Volume 1 and 2 [English]
Chapter 42 Photoelectric Effect and Wave-Particle Duality
MCQ | Q 6 | Page 363

RELATED QUESTIONS

Define the term 'intensity of radiation' in terms of photon picture of light.


Ultraviolet light of wavelength 2271 Å from a 100 W mercury source irradiates a photo-cell made of molybdenum metal. If the stopping potential is −1.3 V, estimate the work function of the metal. How would the photo-cell respond to a high intensity (∼105 W m−2) red light of wavelength 6328 Å produced by a He-Ne laser?


Light of intensity 10−5 W m−2 falls on a sodium photo-cell of surface area 2 cm2. Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about 2 eV. What is the implication of your answer?


The following graph shows the variation of photocurrent for a photosensitive metal : 


(a) Identify the variable X on the horizontal axis.

(b) What does the point A on the horizontal axis represent?

(c) Draw this graph for three different values of frequencies of incident radiation v1, v2 and v3 (v1 > v2 > v3) for same intensity.

(d) Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I1 > I2 > I3) having same frequency.


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


In an experiment on photoelectric effect, a photon is incident on an electron from one direction and the photoelectron is emitted almost in the opposite direction. Does this violate the principle of conservation of momentum?


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?


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.


Let nr and nb be the number of photons emitted by a red bulb and a blue bulb, respectively, of equal power in a given time.


Photoelectric effect supports quantum nature of light because
(a) there is a minimum frequency below which no photoelectrons are emitted
(b) the maximum kinetic energy of photoelectrons depends only on the frequency of light and not on its intensity
(c) even when the metal surface is faintly illuminated the photoelectrons leave the surface immediately
(d) electric charge of the photoelectrons is quantised


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)


A small piece of cesium metal (φ = 1.9 eV) is kept at a distance of 20 cm from a large metal plate with a charge density of 1.0 × 10−9 C m−2 on the surface facing the cesium piece. A monochromatic light of wavelength 400 nm is incident on the cesium piece. Find the minimum and maximum kinetic energy of the photoelectrons reaching the large metal plate. Neglect any change in electric field due to the small piece of cesium present.

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


On the basis of the graphs shown in the figure, answer the following questions :

(a) Which physical parameter is kept constant for the three curves?

(b) Which is the highest frequency among v1, v2, and v3?


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?


In photoelectric effect the photo current ______.


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 figure shows a plot of stopping potential (V0) versus `1/lambda`, where λ is the wavelength of the radiation causing photoelectric emission from a surface. The slope of the line is equal to ______.


  • Assertion (A): For the radiation of a frequency greater than the threshold frequency, the photoelectric current is proportional to the intensity of the radiation.
  • Reason (R): Greater the number of energy quanta available, the greater the number of electrons absorbing the energy quanta and the greater the number of electrons coming out of the metal.

Which of the following options represents the variation of photoelectric current with property of light shown on the x-axis?






Share
Notifications

Englishहिंदीमराठी


      Forgot password?
Use app×