71. The magnifying power of a telescope can be increased by

1. 1. Reducing the focal length of the eye piece

   
   
   

   2. Increasing the diameter of the objective

   
   
   

   3. Reducing the focal length of the objective

   
   
   

   4. Increasing the diameter of the eyepiece

   
   
   

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   N/A

   Correct Option: A

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72. How for must a girl standing front of a concave spherical mirror of radius 120 cm to see an erect image of her face four times its natural size?

1. 1. 40 cm from the mirror

   
   
   

   2. 45 cm from the mirror

   
   
   

   3. 50 cm from the mirror

   
   
   

   4. 55 cm from the mirror

   
   
   

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   N/A

   Correct Option: B

   N/A

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73. Optically active substances are those substances which

1. 1. Produce polarized light

   
   
   

   2. Rotate the plane of polarization of polarized light

   
   
   

   3. Produce double refraction

   
   
   

   4. Convert a plane polarized light into circularly polarized light

   
   
   

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   N/A

   Correct Option: B

   N/A

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74. Why is red light employed for danger signals ?

1. 1. Red colour is soothing to the eye

   
   
   

   2. Human eye is most sensitive to red colour

   
   
   

   3. Red light is scattered least

   
   
   

   4. Red light is scattered most

   
   
   

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   N/A

   Correct Option: C

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75. To observe diffraction, the size of the obstacles

1. 1. Should be of the same order as the wavelength

   
   
   

   2. Should be much larger than the wavelength

   
   
   

   3. Has no relation to wavelength

   
   
   

   4. Should be exactly half the wavelength

   
   
   

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1. View Hint View Answer Discuss in Forum

   N/A

   Correct Option: A

   N/A

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