A concave mirror has a focal length of 40 cm. At what distance from the mirror should a 8 cm tall object be placed so that it forms an image at a distance of 60 cm from the mirror? Also calculate the size of the image formed
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Explanation:
Solution
Givenn u=40 cm (negative)
m=14 (negative for the real image)
a. From m=−vu,−14=−v(−40) or v=-10 cm
Thus the image is formed at a distance 10 cm in front of the mirror.
b. Now from relation 1u+1v=1f
1f=1(−40)+1(−10)
=−540
or f=−405=−8cm
i.e., the focal length of concave mirror is 8cm