An object is kept on the principal axis of a concave mirror of focal length 12 cm. If the object is at a distance of 18 cm from the mirror, calculate the image distance. Determine the nature of the image formed by calculating the magnification produced by the mirror.

Explanation

Concave mirror f = 12 cm
focal length = 12 cm
Object distance = 18 cm
Nature of image = ?
Formula : `(1)/(f) = (1)/(u) + (1)/(v)`
`(1)/(v) = (1)/(f) - (1)/(u)`
`(1)/(v) = (1)/(-12) - (1)/(18)`
`(1)/(v) = -(1)/(12) + (1)/(18)`
`(1)/(v) = - (1)/(36)`
v = - 36
(real image in front of mirror )
magnification = - `(1)/(v)`
= - `((-36))/(18)`
= + 2 (upright )
Nature of iimage : Real and upright image
OR
Power = -0.5 D
nagetive sign means : myopia or short sightedness
Power = `(1)/(f)`
f = `(1)/(-0.5) = - (10)/(5) = -2.0 m xx 100`
= - 200 cm
Concave lens (diverging lens) In myopia, eye is unable to view long distance objects. The image in this case falls before the retina.
For every myopic eye, there exists a far point beyond which clear image cannot be seen. The short-sightedness(myopia) is corrected by using a concave lens which diverges and shifts the image to the retina.