Geometrical OpticsHard
Question
Distance between an object and three times magnified real image is 40 cm . The focal length of the mirror used is $\_\_\_\_$ cm .
Options
A.$- 15/2$
B.-10
C.-20
D.-15
Solution
$m = - 3 = \frac{v}{u}$
$${v = - 3u }{|v| - |u| = 40 }{u = 20\text{ }cm }{v = 60\text{ }cm }{\therefore\frac{1}{v} + \frac{1}{u} = \frac{1}{f} }{\frac{1}{- 60} + \frac{1}{- 20} = \frac{1}{f} }{f = - 15\text{ }cm}$$
Create a free account to view solution
View Solution FreeMore Geometrical Optics Questions
The image of an object, formed by a plano-convex lens at a distance of 8 m behind the lens, is real and is one-third the...A long sighted person has a minimum distance of distinct vision of 50 cm. He wants to reduce it to 25 cm. He should use ...The length of a telescope is 36 cm. The focal lengths of its lenses can be -...A fish rising vertically up towards the surface of water with speed 3 ms-1 observes a bird diving vertically down toward...An object and a screen are fixed at a distance d apart. When a lens length f is moved between the object and the screen,...