An object is placed 18 cm in front of a spherical mirror . If the image is formed at 4 cm to right of mirror . calculate it's focal length . Is the concave or convex ? What is the nature of image and radius of curvature ?
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u = - 18 cm
v = 4 cm
1 / f = 1 / v + 1 / u
1 / f = 1 / 4 + 1 / (- 18)
1 / f = 1 / 4 - 1 / 1 8
1 / f = 9 - 2 / 36 = 7 / 36
f = 36 / 7 cm
focal length is positive so mirror is convex.
R = 2 × 36 / 7
= 72 / 7 cm =10.28 cm
The image formed is diminished, virtual and erect!
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