51. The ozone layer absorbs radiation of wavelengths

1. 1. Less than 3 x 10^-5 m

   
   
   

   2. More than 3 x 10^-7 m

   
   
   

   3. Less than 3 x 10^-5 m

   
   
   

   4. Less than 3 x 10^-5 m

   
   
   

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   NA

   Correct Option: A

   NA

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52. Consider the following statements :
    Assertion (A) : The velocity of sound in air increases due to the presence of moisture in it
    Reason (R) : The presence of moisture in air lowers the density of air of these statements
    Codes

1. 1. Both A and R are true and R is the correct explanation of A

   
   
   

   2. Both A and R are true but R is not the correct explanation of A

   
   
   

   3. A is true but R is false

   
   
   

   4. A is false but R is true

   
   
   

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   NA

   Correct Option: A

   NA

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53. The ionosphere is mainly composed of

1. 1. Nitrogen and oxygen

   
   
   

   2. Ozone

   
   
   

   3. Electrons and positive ions

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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54. If the pressure amplitude of a sound wave is tripled, then the intensity of the wave increased by a factor

1. 1. 3

   
   
   

   2. 6

   
   
   

   3. 9

   
   
   

   4. √3
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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55. When an aeroplane attains a speed higher than the speed of sound in air a loud bang is heared. This is because

1. 1. It explodes

   
   
   

   2. Its wings vibrate so violently that the bang is heard

   
   
   

   3. The normal engine noises undergo a Doppler shift to generate the bang

   
   
   

   4. It produces a shock wave which is received as the bang

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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