0
question_answer1) Define photoelectric work function. How is it related to threshold frequency?
question_answer2) How will you justify that the rest mass of photons is zero?
question_answer3) Do all the photons have same mass? If not, why?
question_answer4) Which photon is more energetic: A red one or a violet one?
question_answer5) If the wavelength of an electromagnetic radiation is doubled, what will happen to the energy of photons?
question_answer6) What happens to the wavelength of a photon after it collides with an electron?
question_answer7) Why are alkali metals most suited as photo-sensitive metals?
question_answer8) Does each incident photon essentially eject an electron?
question_answer9) Is photoelectric emission possible at all Frequencies? Give reason for your answer.
question_answer10) Work function of aluminium is\[\mathbf{4}.\mathbf{2}\text{ }\mathbf{eV}\]. If two photons each of energy \[\mathbf{2}.\mathbf{5}\text{ }\mathbf{eV}\] are incident on its surface, will the emission of electrons take place? Justify your answer.
question_answer11) Out of microwaves, ultraviolet rays and infra-red rays, which radiations will be most effective for emission of electrons from a metallic surface?
question_answer12) Can X-rays cause photoelectric effect?
question_answer13) Two metals A and B have work functions \[\mathbf{4}\text{ }\mathbf{eV}\] and \[\mathbf{10}\text{ }\mathbf{eV}\] respectively. Which metal has higher threshold wavelength?
question_answer14) Ultraviolet light is incident on two photosensitive materials having work functions \[{{W}_{1}}\] and \[{{W}_{2}}({{W}_{1}}>{{W}_{2}})\]. In which case will the kinetic energy of the emitted electrons be greater? Why?
question_answer15) Does the 'stopping potential' in photo- electric emission depend upon (i) the intensity of the incident radiation in a photocell? (ii) the frequency of the incident radiation?
question_answer16) Two beams, one of red light and the other of blue light, of the same intensity are incident on a metallic surface to emit photoelectrons. Which one of the two beams emits electrons of greater kinetic energy?
question_answer17) Electrons are emitted from a photo-sensitive surface when it is illuminated by green light but electron emission does not take place by yellow light. Will the electrons be emitted when the surface is illuminated by (i) red light, and (ii) blue light?
question_answer18) When a monochromatic yellow coloured light beam is incident on a given photosensitive surface, photoelectrons are not ejected, while the same surface gives photoelectrons when exposed to green coloured monochromatic beam. What will happen if the same photo-sensitive surface is exposed to (i) violet and (ii) red coloured, monochromatic beam of light? Justify your answer.
question_answer19) How does the maximum kinetic energy of electrons emitted vary with the work function of the metal?
question_answer20) A source of light is placed at a distance\[\mathbf{50}\text{ }\mathbf{cm}\] from a photo-cell and the cut-off potential is found to be \[{{V}_{0}}\]. If the distance between the light source and photo-cell is made\[\mathbf{25}\text{ }\mathbf{cm}\], what will be the new cut-off potential? Justify your answer.
question_answer21) When monochromatic radiation of wavelength \[\mathbf{2000}\text{ }\overset{\circ }{\mathop{\mathbf{A}}}\,\] falls upon a nickel plate, the latter acquires a positive charge. The wavelength is increased and at\[\mathbf{3400}\text{ }\overset{\circ }{\mathop{\mathbf{A}}}\,\], however intense the monochromatic radiation may be, effect is found to cease. Give reason.
question_answer22) What is the effect on the velocity of photoelectrons, if the wavelength of incident light is decreased?
question_answer23) It is difficult to eject out an electron from copper than sodium. Which of the two metals has greater work function and which has greater threshold wavelength?
question_answer24) The frequency \[\left( \mathbf{v} \right)\] of incident radiation is greater than threshold frequency \[\mathbf{(}{{\mathbf{v}}_{\mathbf{0}}}\mathbf{)}\] in a photocell. How will the stopping potential vary if frequency \[\left( \mathbf{v} \right)\] is increased, keeping other factors constant?
question_answer25) The stopping potential in an experiment on photoelectric effect is\[\mathbf{1}.\mathbf{5}\text{ }\mathbf{V}\]. What is the maximum kinetic energy of the photoelectrons emitted?
question_answer26) The maximum kinetic energy of a photoelectron is\[\mathbf{3}\text{ }\mathbf{eV}\]. What is its stopping potential?
question_answer27) State de-Broglie hypothesis.
question_answer28) What considerations led de-Broglie to suggest that material particles can also show wave property?
question_answer29) Are matter waves electromagnetic? Write de-Broglie equation.
question_answer30) Why are de-Broglie waves associated with a moving football not visible?
question_answer31) What inference was drawn from Davisson and Germer experiment regarding the nature of electrons?
question_answer32) The de-Broglie wavelength of a particle of kinetic energy K is \[\lambda \]. What would be the wavelength of the particle, if its kinetic energy were\[K/4\] ?
question_answer33) The most probable kinetic energy of thermal neutrons at a temperature of T kelvin, may be taken as equal to kT, where k is Boltzmann constant. Taking the mass of a neutron and its associated de- Broglie wavelength as m and \[{{\lambda }_{B}}\] respectively, state the dependence of \[{{\lambda }_{B}}\] on m and T.
question_answer34) Why is a photo-cell also called an electric eye?
question_answer35) On what principle is an electron microscope based?
question_answer36) Write Einstein's photoelectric equation. State clearly how this equation is obtained using the photon picture of electromagnetic radiation. Write the three salient features observed in photoelectric effect which can be explained using this equation. Or What is photo-electric effect? Write Einstein's photoelectric equation. Explain how it enables us to understand the (i) linear dependence, of the maximum kinetic energy of the emitted electrons, on the frequency of the incident radiation. (ii) existence of a threshold frequency for a given photoemitter. (iii) independence of the maximum energy of emitted photo-electrons from the intensity of incident light.
question_answer37) Define the terms (i) 'cut-off voltage' and (ii) 'threshold frequency' in relation to the phenomenon of photoelectric effect. Using Einstein's photoelectric equation show how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.
question_answer38) Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. What information can be obtained from the value of intercept on the potential axis? A source of light of frequency greater than the threshold frequency is placed at a distance of 1 m from the cathode of a photo-cell. The stopping potential is found to be V. If the distance of the light source from the cathode is reduced, explain giving reasons, what change will you observe in the (i) photoelectric current, (ii) stopping potential ?
question_answer39) When a given photosensitive material is irradiated with light of frequency \[\mathbf{v}\], the maximum speed of the emitted photoelectrons equals \[{{\upsilon }_{\max }}\] . The square of \[{{\upsilon }_{\max }},\] i.e., \[\upsilon _{\max }^{2}\] , is observed to vary with \[\mathbf{v}\], as per the graph shown in Fig. Obtain expressions for (i) Planck's constant, and (ii) the work function of the given photosensitive material, in terms of the parameters \[l,n\] and the mass, \[\mathbf{m}\], of the electron.
question_answer40) Sketch the graphs, showing the variation of stopping potential with frequency of incident radiations for two photosensitive materials A and B having threshold frequencies \[v_{0}^{'}>{{v}_{0}},\] respectively. (i) Which of the two metals, A or B has higher work function? (ii) What information do you get from the slope of the graphs? (iii) What does the value of the intercept of graph 'A' on the potential axis represent?
question_answer41) Figure shows the variation of stopping potential \[{{V}_{0}}\] with the frequency \[\mathbf{v}\] of the incident radiation for two photosensitive metals P and \[Q\]: (i) Explain which metal has smaller threshold wavelength. (ii) Explain, giving reason, which metals emits photo electrons having smaller kinetic energy, for the same wavelength of incident radiation. (iii) If the distance between the light source and metal P is doubled, how will the stopping potential charge?
question_answer42) Figure shows variation of stopping potential \[({{V}_{0}})\] with the frequency \[\left( \mathbf{v} \right)\] for two photo- sensitive materials\[{{M}_{1}}\] and \[{{M}_{2}}\]. (i) Why is the slope same for both lines? (ii) For which material will the emitted electrons have greater kinetic energy for the incident radiations of the same frequency? Justify your answer.
question_answer43) Figure (a) shows the variation of the stopping potential \[{{V}_{0}}\] with the frequency \[\left( \mathbf{v} \right)\] of the incident radiations for two different photosensitive materials \[{{M}_{1}}\] and \[{{M}_{2}}\] (i) What are the values of work functions for \[{{M}_{1}}\] and \[{{M}_{2}}\]? (ii) The values of the stopping potential for \[{{M}_{1}}\] and \[{{M}_{2}}\] for a frequency \[{{v}_{3}}(>{{v}_{02}})\]of the incident radiations are \[{{V}_{1}}\] and \[{{V}_{2}}\] respectively. Show that the slope of the lines equals \[\frac{{{V}_{1}}-{{V}_{2}}}{{{v}_{02}}-{{v}_{01}}}\] (a) (b)
question_answer44) Plot a graph showing the variation of stopping potential with the frequency of incident radiation for two different photosensitive materials having work functions \[{{W}_{1}}\] and \[{{W}_{2}}({{W}_{1}}>{{W}_{2}})\]. On what factors does the (i) slope and intercept of the lines depend?
question_answer45) Write two characteristic features observed in photoelectric effect which support the photon picture of electromagnetic radiation. Draw a graph between the frequency of incident radiation \[\left( \mathbf{v} \right)\] and the maximum kinetic energy of the electrons emitted from the surface of a photosensitive material. State clearly how this graph can be used to determine (i) Planck's constant and (ii) work function of the material.
question_answer46) Draw a plot showing the variation of photoelectric current with collector plate potential for two different frequencies,\[{{v}_{1}}>{{v}_{2}},\] of incident radiation having the same intensity. In which case will the stopping potential be higher? Justify your answer.
question_answer47) The graph of Fig. variation of photo-electric current with collector plate potential for different frequencies of incident radiations. (i) Which physical parameter is kept constant for the three curves? (ii) Which frequency \[\text{(}{{\text{v}}_{\text{1}}}\text{,}{{\text{v}}_{\text{2}}}\text{or }{{\text{v}}_{3}}\text{)}\] is the highest?
question_answer48) Figure shows a plot of three curves, a, b, c showing the variation of photocurrent vs. collector plate potential for three different intensities \[{{I}_{1}},{{I}_{2}}\]and \[{{I}_{3}}\] having frequencies \[{{v}_{1}},{{v}_{2}}\]and \[{{v}_{3}}\] respectively incident on a photosensitive surface. Point out the two curves for which the incident radiations have same frequency but different intensities.
question_answer49) How is the photoelectric current affected on increasing the (i) frequency (ii) intensity of the incident radiations and why?
question_answer50) What will happen to: (i) kinetic energy of photoelectrons, and (if) photocurrent, if the light is changed from ultraviolet to X-rays in a photo-cell experiment? Intensity of the beam is the same in both cases.
question_answer51) For a photosensitive surface, threshold wavelength is \[{{\lambda }_{0}}\]. Does photo-emission occur if the wavelength \[(\lambda )\] of the incident radiation is (i) more than\[{{\lambda }_{0}}\] (ii) less than \[{{\lambda }_{0}}\]? Justify your answer.
question_answer52) State how in a photo-cell, the work function of the metal influence the kinetic energy of emitted electrons. (a) If the intensity of incident radiation is doubled, what changes occur in (i) the stopping potential and (ii) the photoelectric current? (b) If the frequency of the incident radiation is doubled, what changes occur in the (i) stopping potential and (ii) photoelectric current?
question_answer53) If the frequency of the incident radiation on the cathode of a photo-cell is doubled, how will the following change: (i) Kinetic energy of the electrons? (ii) Photoelectric current? (iii) Stopping potential? Justify your answer.
question_answer54) Radiation of frequency \[\mathbf{1}{{\mathbf{0}}^{\mathbf{15}}}\] Hz is incident on three photo-sensitive surfaces A, B and C. Following observations are recorded: Surface A: No photo-emission occurs. Surface B: Photo-emission occurs but the photo- electrons have zero kinetic energy. Surface C: Photo-emission occurs and photo- electrons have some K.E. Based on Einstein's photo-electric equation, explain the three observations.
question_answer55) Radiations of frequency 1015 Hz are incident on two photo-sensitive surfaces P and Q. Following observations are made : (i) Surface P: Photo-emission occurs but the photo- electrons have zero kinetic energy, and (ii) Surface Q; Photo-emission occurs and photo- electrons have some kinetic energy. Which of these has a higher work function? If the incident frequency is slightly reduced, what will happen to photo-electron emission in the two cases?
question_answer56) Which two main observations in photoelectricity led Einstein to suggest the photon theory for the interaction of light with the free electrons in a metal? Obtain an expression for the threshold frequency for photoelectric emission in terms of the work function of the metal.
question_answer57) A proton and an alpha particle are accelerated through the same potential. Which one of the two has (i) greater value of de-Broglie wavelength associated with it, and (ii) less kinetic energy? Justify your answer.
question_answer58) An electron and a proton are accelerated through the same potential. Which one of the two has (i) greater value of de-Broglie wavelength associated with it and (ii) less momentum? Justify your answer.
question_answer59) An electron, \[\alpha \]-particle and a proton have the same kinetic energy. Which of these particles has the shortest de-Broglie wavelength?
question_answer60) An \[\alpha \]-particle and a proton are accelerated through the same potential difference. Calculate the ratio of linear momenta acquired by the two.
question_answer61) Mention the significance of Davisson- Germer experiment. An \[\alpha \]-particle and a proton are accelerated from rest through the same potential difference\[\mathbf{V}\]. Find the ratio of de-Broglie wavelengths associated with them.
question_answer62) The two lines A and B shown in the graph plot the de-Broglie wavelength \[(\lambda )\] as a function of \[1/\sqrt{V}\] (V is the accelerating potential) for two particles having the same charge. Which of the two represents the particle of heavier mass?
question_answer63) Calculate the de-Broglie wavelength associated with an electron of energy\[\mathbf{200}\text{ }\mathbf{eV}\]. What will be the change in this wavelength if the accelerating potential is increased to four times its earlier value?
question_answer64) What reasoning led de-Broglie to put forward the concept of matter waves? The wavelength, \[\lambda \], of a photon, and the de-Broglie wavelength associated with a particle of mass 'm', has the same value, say \[\lambda \]. Show that the energy of photon is \[\frac{2\lambda mc}{h}\] times the kinetic energy of the particle.
question_answer65) An electron and a photon have same de- Broglie wavelength (say\[\overset{\mathbf{o}}{\mathop{\mathbf{A}}}\,\]). Which one possesses more kinetic energy? Or Compare the energy of an electron of de-Broglie wavelength \[1\overset{\mathbf{o}}{\mathop{\mathbf{A}}}\,\] with that of an X-ray photon of the same wavelength.
question_answer66) An electron and a photon each have de-Broglie wavelength of\[\mathbf{1}.\mathbf{00}\text{ }\mathbf{nm}\]. (i) Write the ratio of their linear momenta, (ii) Compare the energy of the photon with the kinetic energy of the electron.
question_answer67) Calculate the ratio of the accelerating potential required to accelerate (i) a proton and (ii) an \[\alpha \] -particle to have the same de-Broglie wavelength associated with them. [Given : Mass of proton \[=1.6\times {{10}^{-27}}\] kg ; Mass of \[\alpha \] -particle\[=6.4\times {{10}^{-27}}\] kg]
question_answer68) An electron and a proton have the same de-Broglie wavelength. Which one of these has higher kinetic energy? Which one is moving faster?
question_answer69) An electron and a proton have same wavelength. Which one possesses more energy?
question_answer70) An electron and photon have same wavelength. Which one of the two has more energy?
question_answer71) The speed of electrons in an electron microscope is\[\mathbf{1}{{\mathbf{0}}^{\mathbf{8}}}\mathbf{m}{{\mathbf{s}}^{\mathbf{-1}}}\]. If protons with the same speed are used instead of electrons, what additional advantage such a proton microscope has over an electron microscope?
Please Wait you are being redirected....
You need to login to perform this action.You will be redirected in 3 sec
OTP has been sent to your mobile number and is valid for one hour
Your mobile number is verified.