141. Glass has refractive index 3 / 2 and water has refractive index 4 / 3. If the speed of light in glass is 2.00 X 10⁸ m/s, the speed of light in water in m/s is

1. 1. 1.5 X 10⁸

   
   
   

   2. 1.78 X 10⁸

   
   
   

   3. 2.25 X 10⁸

   
   
   

   4. 2.67 X 10⁸

   
   
   

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   N/A

   Correct Option: C

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142. Spherical aberration in a thin lens can be reduced by

1. 1. Using a monochromatic light

   
   
   

   2. Using a doublet combination

   
   
   

   3. Using a circular annular mark over the lens

   
   
   

   4. Increasing the size of the lens

   
   
   

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   N/A

   Correct Option: C

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143. A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms areal image. The hew image

1. 1. Is closer to the lens system

   
   
   

   2. Is farther from the lens system

   
   
   

   3. Is at the original position

   
   
   

   4. None of the above

   
   
   

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   N/A

   Correct Option: B

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144. If f_b and f_g are the focal lengths of a convex lens for blue and red lights respectively and f_b and f_r are the respective value for a concave lens, then

1. 1. f_b > f_r and f_b > f_r

   
   
   

   2. f_b < f_r and f_b < f_r

   
   
   

   3. f_b > f_r and f_b < f_r

   
   
   

   4. None of these

   
   
   

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   N/A

   Correct Option: B

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145. To an observer on the earth the stars appear to twinkle. This can be described to

1. 1. The fact that stars do not emit light continuously own atmosphere

   
   
   

   2. Frequent absorption of star light by earth's atmosphere

   
   
   

   3. Frequent absorption of star light by their own atmosphere

   
   
   

   4. The refractive index fluctuations in earth's atmosphere

   
   
   

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1. View Hint View Answer Discuss in Forum

   N/A

   Correct Option: D

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