CBSE Class 12th Physics Chapter 11 - Dual Nature of Radiation and Matter Important Questions with Answers
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State two properties of photons. For a monochromatic radiation incident on a photosensitive surface, why do all photoelectrons not come out with the same energy? Give reason for your answer.
(Comptt. All India 2017)
Question 2.
A photon and a proton have the same de-Broglie wavelength. Show, by actual calculations, which has more total energy. (Comptt. All India 2017)
Question 3.
(i) How does one explain the emission of electrons from a photosensitive surface with the help of Einstein’s photoelectric equation?
(ii) The work function of the following metals is given : Na = 2.75 eV, K = 2.3 eV, Mo = 4.17 eV and Ni 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 A from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away? (Delhi 2017)
Question 4.
In the study of a photoelectric effect the graph between the stopping potential V and frequency v of the incident radiation on two different metals P and Q is shown here:
(i) Which one of the two metals has higher threshold frequency?
(ii) Determine the work function of the metal which has greater value.
(iii) Find the maximum kinetic energy of electron emitted by light of frequency 8 × 1014 Hz for this metal. (Delhi 2017)
Question 5.
(i) State two important features of Einstein’s photoelectric equation.
(ii) Radiation of frequency 1015 Hz is incident on two photosensitive surfaces P and Q. There is no photoemission from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface Q. (Delhi 2017)
Question 6.
Using photon picture of light, show how Einstein’s photoelectric equation can be established. Write two features of photoelectric effect which cannot be explained by wave theory. (All India 2017)
Question 7.
Explain giving reasons for the following:
(a) Photoelectric current in a photocell increases with the increase in the intensity of the incident radiation.
(b) The stopping potential (V0) varies linearly with the frequency (v) of the incident radiation for a given photosensitive surface with the slope remaining the same for different surfaces.
(c) Maximum kinetic energy of the photoelectrons is independent of the intensity of incident radiation. (All India 2017)
Question 8.
The given 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. (All India 2017)
Question 9.
Draw a graph showing the variation of de Broglie wavelength of a particle of charge q and mass m with the accelerating potential. Proton and deuteron have the same de Broglie wavelengths. Explain which has more kinetic energy. (Comptt. Delhi 2017)
Question 10.
(a) Draw the graph showing the variation of de Broglie wavelength of a particle of charge q and mass m with the accelerating potential.
(b) An electron and proton have the same de Broglie wavelengths. Explain, which of the two has more kinetic energy. (Comptt. Delhi 2017)
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Question 1.
Draw a graph showing the variation of de Broglie wavelength ? of a particle of charge q and mass m, with the accelerating potential V. An ?-particle and a proton have the same de-Broglie wavelength equal to 1Å. Explain with calculations, which of the two has more kinetic energy. (Comptt. Delhi 2017)
Question 2.
The photon emitted during the de-excitation from the 1st excited level to the ground state of hydrogen atom is used to irradiate a photo cathode of a photocell, in which stopping potential of 5 V is used. Calculate the work function of the cathode used. (Comptt. All India 2017)
Question 3.
An electron microscope uses electrons accelerated by a potential difference 50 kV. Calculate the de Broglie wavelength of the electrons. Compare the resolving power of an electron microscope with that of an optical microscope, which uses visible light of wavelength 550 nm. Assume the numerical aperture of the objective lens of both microscopes are the same. (Comptt. All India 2017)
Question 4.
(a) Write three observed features of photoelectric effect which cannot be explained by wave theory of light.
Explain how Einstein’s photoelectric equation is used to describe these features satisfactorily.
(b) Figure shows a plot of stopping potential (v0) with frequency (v) of incident radiation for two photosensitive materials M1 and M2.
Explain
(i) why the slope of both the lines is same?
(ii) for which material emitted electrons have greater kinetic energy for the same frequency of incident radiation? (Comptt. All India 2017)
Question 5.
(a) Describe briefly how wave nature of moving electrons was established experimentally.
(b) Estimate the ratio of de-Broglie wavelength associated with deuterons and a-particles when they are accelerated from rest through the same accelerating potential V. (Comptt. All India 2017)
Question 6.
Write three characteristic features in photoelectric effect which cannot be explained on the basis of wave theory of light, but can be explained only using Einstein’s equation. (Delhi 2016)
Question 7.
Sketch the graph showing variation of stopping potential with frequency of incident radiations for two photosensitive materials A and B having threshold frequencies vA > vB.
(i) In which case is the stopping potential more and why?
(ii) Does the slope of the graph depend on the nature of the material used? Explain. (All India 2016)
Question 8.
The graphs, drawn here, are for the phenomenon of photoelectric effect.
(i) Identify which of the two characteristics (intensity/frequency) of incident light, is being kept constant in each case.
(iii) Justify the existence of a ‘threshold frequency’ for a given photosensitive surface. (Comptt. Delhi 2016)
Question 9.
Point out two distinct features observed experimentally in photoelectric effect which’ cannot be explained on the basis of wave theory of light. State how the ‘photon picture’ of light provides an explanation of these features. (Comptt. All India 2016)
Question 10.
A proton and an a-particle have the same de- roglie wavelength. Determine the ratio of
(i) their accelerating potentials
(ii) their speeds. (Delhi 2015)
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