2nd Year Physics Chapter 19 Dawn of Modern Physics Notes MCQs Solutions

physics 12th notes mcqs chapter 19

1. The rest mass energy of an electron is


2. The experimental evidence for the existence of de-Broglie
wavelength with moving object was a consequence of the


3. On a hot day or in hot climates white clothes are worn because
they are good


4. The stopping potential for a certain metal is 10 volts, then the
work function for the cathode is


5. Which of following waves do not travel at speed of light?


6. 0.1kg will be equivalent to the energy


7. Absolute motion cannot be detected:    


8. If the energy of photon is 10 eV and work function is 5 eV, then the a value of stoppi will be:


9. Due to relative motion of observer and the frame of reference of events time always:


10. When the K.E max of photoelectron is zero, the frequency of incident photon is That of threshold frequency


11. The radiations of longer wavelength:


12. Compton considered that x-rays consist of:                 


13. In 1905 the theory of relativity was proposed by


14. The speed of light in free space is:                     


15. At what speed would the mass of an electron become double of its rest mass?


16. The uncertainty principle relates uncertainties in the measurements of energy and:


17. Davison and Germer indicate_____in their experiment


18. Which of the following can be studied with γ-rays


19. Emission of electron by metals on heating is called


20. The amount of energy to create an electron-positron pair is
equal to


21. The wavelength corresponding to maximum intensity of radiation shifts steadily towards shorter wavelength choose among following:


22. Positron was discovered by


23. Has the largest de Broglie wavelength at same speed.


24. A photon is a:


25. Wave nature of light appears in


26. A non-inertial frame of reference is that:                       


27. In SI units, the value of Wien’s constant is:


28. If a material object moves with speed of light, its mass becomes


29. The special theory of relativity is applicable to the object moving with maximum velocity equal to: 


30. Absorption power of a perfect black body is


31. Any coordinate system relative to which results are taken is known as:


32. At low temperature, the hot body emits the radiation of:


33. Earth is considered as:                                                    


34. At high temperature, a body emits radiations of:         


35. The nature of radiation emitted from a hot body depends upon:


36. In photoelectric effect, light exhibits


37. When the stopping potential is applied to the anode of photocell, no current is ab mean:


38. The work function for photoelectric effect:


39. Amount of energy released due to complete breaking of 1 kg
matter is


40. The special theory of relativity is based upon: 


41. Wave nature of light is revealed by


42. An observer sitting in an aeroplane and moving with very high speed observes the mass of the object at rest with respect to it.
He finds its mass to be


43. The best metal to be used for photoemission is:


44. The Davison and Germer experiment relates to:          


45. In a annihilation, emitted photon move in opposite direction to conserve


46. At high temperature, the hot body emits the radiation of:


47. The classical physics is based on the laws of:


48. The uncertainty principle applicable to:             


49. Which is the most refined form of matter?


50. The number of photoelectrons ejected is


51. In Compton effect, the wavelength of scattered photons as compared to the wavelength of incident x-rays is:


52. The total amount of energy radiated per unit orifice area of
cavity radiator per unit time is directly proportional to


53. The relation between work function and maximum energy of photoelectrons was discovered by:


54. When light falls on a metal surface, photo electrons are emitted. If the intensity of the light is increased, which of the following will increase


55. If energy of photon is E its equivalent to mass


56. Particle nature of light is revealed by


57. Pair production takes place only when the energy of the photon
fulfills the condition that hf is


58. A body emits radiation which is of long or wavelength in visible infrared region at:


59. Platinum wire at 1300 °C becomes


60. The energy of a photon is given by


61. Electron microscope makes practical use of the


62. Threshold frequency is the:


63. The reverse phenomenon of photoelectric effect is


64. If speed of light were infinite then moving mass m=


65. Which one of the following scientists regarded light as electromagnetic waves:


66. A photocell can be used to operate:


67. If the momentum of particle is doubled, than its de-Broglie wavelength:


68. Who explained the photo electric effect?


69. Wave nature of light appears in


70. When a platinum wire heated at about 500 0C, it becomes


71. The speed of light (3 x 10⁸ m sec⁻¹) in free space is


72. Which light photon has the least momentum?


73. Einstein’s mass energy relation is


74. The velocity of the photoelectron depends upon:


75. In Davison and Germer expert, the angle which the incident beam makes with the normal to the nicked crystal is:


76. Rest mass energy of electron-positron pair is


77. The photoelectric effect predicts that light is made of:


78. If a platinum wire is heated at 500° C, then it appears as:


79. If a particle of mass m is moving with a speed v, then the
deBroglie wavelength associated with it will be


80. In photoelectric effect which factor increases by increasing the intensity of incident photon?


81. Einstein explained the photo-electric effect on the following assumption that


82. Which one of the following statements is true for photoelectric experiment


83. Blue light has frequency 7.5×1014 Hz. Its energy is


84. Potassium cathode in photocell emits electrons for a light:


85. Which one of the following require a material medium for their propagation


86. According to special theory of relativity, mass and energy are different quantities and:


87. Point out the formulation that does not depend the choice of reference frames:


88. An inertial frame of reference is that one


89. The work function of the metal will be:


90. If the photoelectric current is goes on decreasing it means that:


91. The SI unit of Plank’s constant is


92. The mass of an object will be doubled at speed


93. In Compton scattering, the change in wavelength will be
maximum when angle of scattering θ=


94. The ratio of the energy E to the corresponding frequency f of the radiation emitted or absorbed is known as:


95. Which of the following makes use of photoelectric effect:


96. Theory of relativity which deals with non-inertial frame of reference is


97. For a black body, the product ofkm and T known as:


98. The Davison and Germer experiment indicates


99. The value of Plank’s constant h is:


100. All motions are:                 


101. The platinum wire becomes white at a temperature of


102. The concept of direction is purely:                     


103. Which phenomenon proves the particle nature of electromagnetic waves?


104. The electron was discovered by


105. Einstein was awarded Nobel Prize in Physics in:


106. Einstein’s photoelectric equation is given by


107. The speed of light in free space regardless of the state of motion
of the observer is


108. When electron and positron are annihilated, the number of
photons produced


109. Photoelectric effect can be explained by


110. When platinum wire is heated, then it become ______at temperature 5000 C.


111. The study of photoelectric effect is useful for understanding:


112. The part of special theory of relativity which deals with the
accelerated motion is called


113. A black body spectrum of radiation is an example of:


114. The phenomenon of photoelectric effect was first explained by:


115. If an object moves with speed of light, then its apparent length becomes:


116. In Sl units the value of Stefen’s constant is:                  


117. The process through which photons can interact with matter is:


118. From m =  that to get even a small increase in mass of an object, we require:


119. The name of the photon for a quantum of light was proposed by


120. The way through which electromagnetic radiation or photons interact wit 7/16 their:


121. Einstein explained the photo-electric effect on the following assumption that


122. Mathematical formulation for electromagnetic waves is given the name:


123. Inertial frame is a frame in which


124. As the temperature of a black body is raised, the wavelength
corresponding to maximum intensity


125. The nature of radiation emitted by a body depends upon:


126. The special theory of relativity is applicable to the objects moving with maximum velocity:


127. Which one of the following physical quantities change with relativistic speed:


128. The electrons behave as waves because they can be:


129. The value of Wien percent s constant is measured in:


130. While demonstrating the photoelectric effect the stopping potential is achieved when:


131. Joule-second is the unit of


132. Radiations are always emitted or absorbed in the form of
packets of energy. This is a statement of


133. The unit of work function is:        


134. Energy of black body radiation depends upon:


135. At low temperature, a body generally emit radiations of:


136. Piatinum wire becomes yellow at a temperature of:


137. Using relativistic effects the location of an air craft after an hr flight can be predicted


138. In Davison and Germer experiment, nickel crystal acts as a:


139. The amount of photoelectric current depends upon:


140. The antiparticle of electron is


141. An electric eye operates because of


142. Photons approach each other, their relative speed will be:


143. The coordinate system in which law of inertia is valid is called:


144. Radiations emitted by a human body at normal temperature (370 C) lies in:


145. of ejected photo electrons, there should be an increase Intensity Radiation


146. In Davison and Germer experiment, the angle between incident beam and diffracted beam called:


147. Mass of an object is:


148. Absorption Power of a perfect black body is always:


149. Joule-second is the unit of


150. The pair production and annihilation of matter are


151. The amount of energy required to eject an electron from a
metal surface is called


152. The cut off voltage is independent of intensity of incident light if:


153. According to special theory of relativity all laws of physics are same in all:


154. Which one of the following physical quantities change with
relativistic speed


155. Due to the relative motion of observer and frame of reference, time:


156. Aging process of a human body:


157. Black colour is:                  


158. A positron is an antiparticle of


159. Tick the correct statement


160. The uncertainty principle is applicable only when:


161. When an object moves with speed of light, its length:


162. The minimum energy required by a photon to create an
electron-positron pair is


163. The mathematical meaning to the position of an object was given by


164. The de-Broglie wavelength of a particle is


165. Max Planck awarded the noble prize for his discovery of energy quanta in. 


166. The stopping voltage in photoelectric effect depends upon:


167. When the atomic particles are moving with velocities approaching that of light:


168. If an object moves with speed of light, its mass becomes:


169. In photoelectric emission, the energy of emitted electron is:


170. The magnitude of Plank’s constant is


171. Antiparticle of electron is


172. Einstein was received the noble prize in the basis of:


173. Which one of the following paved the way for modern physics:


174. The idea of matter waves was given by:            


175. Wave nature of light appears in


176. The uncertainty principle was given by:            


177. Earth orbital speed is:      


178. The existence of ether wind was experimentally rejected by


179. In annihilation of matter, an electron and a positron combine to
produce two gamma ray photons in opposite direction for


180. The momentum of a photon of frequency f is


181. A non-inertial frame of reference is that one


182. Which conservation law is obeyed in Einstein photoelectric equation:


183. Newton’s laws of motion are valid:                     


184. The uncertainty in the location of a particle is equal to its de-Broglie wavelength, then uncertainty in its velocity will be equal to:


185. The uncertainty principle is significant for:


186. The maximum kinetic energy of emitted photoelectrons
depends upon


187. If mass of particle is m₀ and relativistic mass is m, then its kinetic
energy is


188. (K.E)max=hf-hf0 is known as


189. In Compton scattering, the change in the wavelength is given by


190. The maximum number of the photoelectrons released in photocell is independent of:


191. When platinum wire is heated, then it becomes_____at temperature about 1600°C:


192. By using NAVSTAR speed of an object can now be determined to an accuracy of:


193. When Platinum is heated, it becomes orange at:


194. Light was considered as electromagnetic waves by the scientist:


195. Compton’s scattering experiment provides a proof that
radiation has a


196. Dimensional representation of Planck’s constant is the same as


197. In photoelectric effect , γ-rays are completely absorbed with the
emission of


198. The uncertainty principle points out that


199. 0.1 kg is equivalent to the energy of


200. The photoelectric threshold frequency depends upon


201. This is a statement of:


202. Which one of the following waves require a material medium for their propagation:


203. Which is a good absorber of heat radiation would be:


204. The dilation of time applies to the timing process which are:


205. A device based on photoelectric effect is called


206. The radius of atom is of the order of


207. Rest mass of a photon is


208. The photoelectric current depends upon:


209. The momentum of the moving photon is


210. According to the uncertainty principle, the mathematical
relation between position and momentum is given by


211. The minimum energy required to create pair production is


212. We can find from de Broglie formula:


213. Maximum kinetic energy of photo electrons depends upon


214. Electron microscope makes use of electron beam because
energetic electrons have


215. Plank’s Quantum concept was used by


216. Black bodies are formed of:         


217. In which of the following phenomenon, the electromagnetic
radiations show particle property


218. Number of electrons emitted in photoelectric effect depends upon:


Short Questions

1. A beam of red light and a beam of blue light have exactly the same energy. Which beam contains the greater number of photons?
2. Air is named as free space ?
3. As a solid is heated and being to glow, why does it first appear red?
4. Can an instant beam of television waves focused on a metal plate cause photo – electric emission? Explain.
5. Can pair production take place in vacuum ?
6. Can photo – electric effect takes place with a free electron?
7. Define pair production ?
8. Define radiation ?
9. Describe some important results of the photo –electric effect?
10. Describe some important use of photocell?
11. Describe the important results concluded from Einstein’s special theory of relativity?
12. Does the brightness of a beam of light primarily depends on the frequency of photons or on the number of photons?
13. Does the dilation mean that time really passes more slowly in moving system or that it only seems to pass the slowly?
14. Give the Max plank’s explanation of the radiation emitted by a black body ?
15. How the uncertainty principle between energy and time is related ?
16. If an electron and a proton have the same de Broglie wavelength, which particle has greayter speed?
17. If ‘E’ and ‘P’ are the energy and momentum of a photon, calculate the velocity of light?
18. If electrons behaved only like particles, what pattern would you except on the screen after the electrons pass through the double slit?
19. If the following particles all have small energy, which has the shortest wave length? Explain, alpha particle, neutron and proton.
20. If the speed of light were infinite, what should be the equations of special theory of relativity reduce to?
21. If we keep on applying force on a material object, can it gain the speed of light?
22. If you are moving in a spaceship at a very high speed relative to the Earth, would you notice a difference (a) I your plus rate (b) in the plus rate of people on the Earth?
23. In what direction, the length contraction happens ?
24. Is it possible to create a single electrons from energy?
25. It is harder to remove a free electron from copper than sodium. Which metal has greater work function? Which metal higher threshold frequency?
26. Measurements show a precise position for an electron, can those measurements shows precise momentum also? Explain.
27. Photo – electric emission occurs only for a definite frequency of light, What this particular frequency is called? Will the number of electrons emitted per second depend n the intensity of light if its frequency is greater than the particular frequency?
28. Photon A has twice the energy of photon B. What is the ratio of the momentum of A to that of B?
29. Whether the electrons are emitted with different energies in photoelectric effect?
30. Since mass is a form of energy can we conclude that a compressed spring has more mass than the same spring when it is not compressed?
31. State Compton effect?
32. State Heinsenberg uncertainty principle ?
33. State law of inertia ?
34. State Stephen-boltzmann’s law ?
35. State the postulates of special theory of relativity?
36. State wien’s displacement law ?
37. Suppose you are standing at the platform and a train passes by you. A passenger sitting in the train and you are looking at a clock on the train. Who measures the proper time interval? You or the passenger? Justify tour answer.
38. The length of a space craft may vanish if it moves with the speed of light. Explain ?
39. Velocity of light is the greatest possible velocity for material bodies. Explain the statement?
40. volts. Find the work function for the cathode plate ?
41. We do not notice the de Broglie wavelength for a pitched cricket ball. Explain Why?
42. What advantages and electron microscope has over an optical microscope ?
43. What amount of energy is needed to carry out phenomenon of pair production ?
44. What are photoelectrons ?
45. What are photons ?
46. What are quanta ?
47. What are the important results concluded from Einstein’s ?
48. What are the measurements on which two observers in relative motion will always agree upon?
49. What aspect of light can be verified by Compton scattering experiment?
50. What do you mean by general theory of relativity ?
51. What do you understand by work function and stopping potential (cut off potential)?
52. What happens to total radiations from a blackbody of its absolute temperature is doubled?
53. What is a black body?
54. What is a frame of reference ?
55. What is a photocell?
56. What is a positron?
57. What is a relation for the momentum of photon in term of wave length ?
58. What is a relation for the momentum of photon is term of frequency ?
59. What is an inertial frame of reference?
60. What is annihilation of matter?
61. What is black body?
62. What is Compton shift?
63. What is Compton wave length ?
64. What is cut off or stopping potential?
65. What is difference between rest and motion ?
66. What is Einstein’s energy mass relation ?
67. What is electron microscope ?
68. What is modern physics ?
69. What is non-inertial fame of reference ?
70. What is photoelectric current ?
71. What is photoelectric effect?
72. What is proper length ?
73. What is relative motion ?
74. What is special theory of relativity?
75. What is the Campton shift in the wavelength of a photon scattered at an angle of 900?
76. What is the colour of a black body which emits all the wave lengths in the visible spectrum of electromagnetic waves ?
77. What is the mathematical form of uncertainty principle ?
78. What is the numerical value of ħ ?
79. What is the relation for relativistic length ?
80. What is the relation for relativistic mass ?
81. What is the relativistic time ?
82. What is the rest mass energy?
83. What is the speed of light in free space ?
84. What is the value of plank’s constant ?
85. What is the value of stephen’s constant ?
86. What is threshold frequency for a metal ?
87. What is work function ?
88. What laws should be conserved during the phenomenon of pair production ?
89. What phenomena may occur when electromagnetic waves interact with the matter?
90. What type of frame of reference in earth?
91. What type of nature of light is confirmed by photoelectric effect?
92. What was the outcome of phenomenon of pair production ?
93. When Compton shift is equal to Compton wave length ?
94. When does light behave as a wave? When does it behave as a particle?
95. When light shines on a surface, is momentum transferred to the metal surface?
96. When the special theory of relativity was proposed ?
97. When ultraviolet light falls on certain dyes, visible light is emitted. Why does this not happen when infrared light falls on these dyes?
98. When was Albert Einstein awarded the Nobel prize ?
99. When was Arthur Holly Compton awarded the Nobel prize ?
100. When was de-Broglie received the Nobel prize ?
101. When was Max plank awarded the Nobel prize ?
102. Whether a black body is an ideal absorber or an ideal radiator ?
103. Whether the mass of an object depends upon its speed ?
104. Whether the mass of an object is a varying quantity ?
105. Whether the phenomenon of black body radiation can be explained by classical physics ?
106. Whether threshold frequency varies from metal to metal ?
107. Whether time is an absolute quantity according to special theory of relativity ?
108. Which has the lower energy quanta? Radio waves or X rays?
109. Which one of the two basic postulates of theory of relativity is more important ?
110. Which photon, red, green, or blue carries the most (a) energy and (b) momentum?
111. Why can red light be used in a photographic dark room when developing films but a blue or white light cannot?
112. Why don’t we observe a Compton Effect with visible light?
113. Why is photo – electric effect so sensitive to the nature of the metal surface?
114. Why must the rest mass of a photon be zero?
115. Will bright light eject more electrons from a metal surface than dimmer light of the same color?
116. Will higher frequency light eject greater number of electrons than low frequency light?
117. Would it be more convenient to demonstrate photoelectric effect with ultra – violet or visible light? Explain.
118. Would it be more convernient to demonstrate photoelectric effect with ultra-violet light or visible light ?
119. Writ the relation for maximum K.E. of photoelectron ?
120. Write some factors upon which photoelectric effect depends?
121. Write some important factors upon which photoelectron effect depends ?
122. Write some important uses of photocells?
123. Write the Compton equation, showing the frequency of scattered photon ?
124. Write the Einstein’s photoelectric equation?

Long Questions

1. Define frame of reference with its type. State postulates of special theory of relativity. Explain three results of theory.
2. What is black body radiation? Explain intensity distribution diagram.
3. What is photoelectric effect? What are its experiment results? How Einstein explained it on the basis of quantum theory?
4. What is photocell? Explain Compton effect.
5. Explain pair production and annihilation of matter.
6. Describe the wave nature of particles. Also discuss Davisson and Germer experiment.
7. Describe the wave particle duality.
8. Write a note on electron microscope.
9. State and prove the Heisenberg uncertainty principle.
10. A particle called the pion lives on the average only about 2.6 x 10⁻⁸s when at rest in the laboratory. It then changes to another form. How long would such a particle live when shooting through the space at 0.95c?
11. What is the mass of a 70kg man in a space rocket traveling at 0.8c from us as measured from Earth?
12. Find the energy of photon in (a) Radiowave of wavelength 100m (b) Green light of wavelength 550nm (c) X-ray with wavelength 0.2nm.
13. Yellow light 577nm wavelength is incident on a cesium surface. The stopping voltage is found to be 0.25 V. Find (a) the maximum K.E. of the photoelectrons (b) the work function of cesium.
14. X-rays of wavelength 22pm are scattered from a carbon target. The scattered radiation being viewed at 85 degree to the incident beam. What is Compton shift?
15. A 90 KeV X-ray photon is fired at a carbon target and Compton scattering occurs. Find the wavelength of the incident photon and the wavelength of the scattered photon for scattering angle of (a) 30 (b) 60.
16. What is the maximum wavelength of the two photons produced when a positron annihilates an electron? The rest mass energy of each is 0.51 MeV.
17. Calculate the wavelength of (a) a 140 g ball moving at 40 ms⁻¹ (b) a proton moving at the same speed (c) an electron moving at the same speed.
18. What is the de Broglie wavelength of an electron whose kinetic energy is 120 eV?
19. An electron is placed in a box about the size of an atom that is about 1 x 10⁻¹⁰m. What is the velocity of the electron?

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