Optics 7 Question 14

14. A container is filled with water (μ=1.33) up to a height of 33.25cm. A concave mirror is placed 15cm above the water level and the image of an object placed at the bottom is formed 25cm below the water level. The focal length of the mirror is

(2005, 2M)

(a) 10cm

(b) 15cm

(c) 20cm

(d) 25cm

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Solution:

  1. Distance of object from mirror

=15+33.251.33=40cm

Distance of image from mirror =15+251.33

=33.8cm

For the mirror, 1v+1u=1f

133.8+140=1ff=18.3cm

Most suitable answer is (c).



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