21. 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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   NA

   Correct Option: D

   NA

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22. 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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23. 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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24. The cathode ray particles originate in a discharge tube from the

1. 1. Cathode

   
   
   

   2. Anode

   
   
   

   3. Source of high voltage

   
   
   

   4. Residual gas

   
   
   

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   NA

   Correct Option: A

   NA

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25. A photo sensitive material would emit electrons, if excited by photons beyond a threshold. To overcome the threshold, one would increase

1. 1. The voltage applied to the light source

   
   
   

   2. Intensity of light

   
   
   

   3. The wavelength of light

   
   
   

   4. The frequency of light

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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