11. The echo will be heard if the original sound reflected by an obstacle in

1. 1. 10 s

   
   
   

   2. 0.50 s

   
   
   

   3. 15 s

   
   
   

   4. 0.1 s

   
   
   

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   NA

   Correct Option: D

   NA

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12. The waves used for a communication through artificial satellites are

1. 1. Microwaves

   
   
   

   2. Radio waves in the AM band

   
   
   

   3. Radio waves in the FM band

   
   
   

   4. None of the above

   
   
   

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   NA

   Correct Option: A

   NA

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13. Consider the following statements

1. 1. 1. A flute of smaller length produces waves of lower frequency.
      2. Sound travels in rocks in the of longitudinal elastic waves only.
      Which of the statements given above is / are correct ?

   
   
   

   2. 1 only

   
   
   

   3. 2 only

   
   
   

   4. both 1 and 2

   
   
   

   5. Neither 1 nor 2

   
   
   

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   NA

   Correct Option: B

   NA

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14. Consider the following parts of spectra
    1. Visible
    2. Infrared
    3. Ultraviolet
    4. Microwave
    Which one of the following is the correct sequence in which their wavelength increase ?

1. 1. 4 - 3 - 1 - 2

   
   
   

   2. 4 - 1 - 2 - 3

   
   
   

   3. 3 - 2 - 1 - 4

   
   
   

   4. 3 - 1 - 2 - 4

   
   
   

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   NA

   Correct Option: D

   NA

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15. The frequencies of X - rays, y-rays and ultraviolet rays are respectively a, b and c then

1. 1. a < b, b > c

   
   
   

   2. a > b, b > c

   
   
   

   3. a > b, b < c

   
   
   

   4. a < b, b < c

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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