76. Radioactivity was discovered by

1. 1. J.J. Thomson

   
   
   

   2. W. Roentgen

   
   
   

   3. H. Becquerel

   
   
   

   4. M. Curie

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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77. Photocells are used for the

1. 1. Reproduction of pictures from the cinema film

   
   
   

   2. Reproduction of sound from the cinema film

   
   
   

   3. Automatic switching of street light

   
   
   

   4. (b) and (c) both

   
   
   

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   NA

   Correct Option: D

   NA

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78. Photoelectric effect can be explained by assuming that light

1. 1. Is a form of transverse wave

   
   
   

   2. Is a form of longitudinal wave

   
   
   

   3. Can be polarised

   
   
   

   4. Consists of quanta

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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79. Consider the following statements
    1. Atom bomb is based upon the principle of uncontrolled nuclear fusion
    2. Hydrogen bomb is based upon the principle of uncontrolled nuclear fission
    3. Nuclear reactor is based upon the principle of controlled nuclear fission
    Which of the statements given above is / are correct ?

1. 1. 3 only

   
   
   

   2. 1 and 2 only

   
   
   

   3. 2 and 3 only

   
   
   

   4. 1, 2 and 3

   
   
   

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   NA

   Correct Option: A

   NA

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80. Photoelectric effect supports quantum nature of light because

1. 1. There is a minimum frequency of light below which no photoelectrons are emitted

   
   
   

   2. The maximum KE of photoelectrons depends only on the frequency of light and hot on its intensity

   
   
   

   3. Even when the metal surface is faintly illuminated, the photoelectrons leave the surface immediately

   
   
   

   4. Electric charge of the photoelectrons is quantised

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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