An object is placed on the principal axis of a convex lens of focal length 10 cm. If the distance of the object from the lens is 30 cm, what is the distance of the image formed?

Question

Question

This question was previously asked in

RRB ALP CBT I 17 Aug 2018 Shift 2 Official Paper

Answer 1

The correct answer is 15 cm.

Key Points

Lens: The transparent curved surface which is used to refract the light and make an image of any object placed in front of it is called a lens.
Convex lens: A lens having two spherical surfaces, bulging outwards is called a double convex lens (or simply convex lens).
- It is thicker in the middle as compared to the edges.
Convex lenses converge light rays and hence, convex lenses are also called converging lenses.
The lens formula is:
- \(\frac{1}{{\rm{v}}} - \frac{1}{{\rm{u}}} = \frac{1}{{\rm{f}}}\)
Magnification
- \(m = \frac v u\)
Where, v = Distance of image, u = Distance of object, f = Focal length

Calculation:

Given:
- u = - 30 cm, f = 10 cm
- Using, \(\frac{1}{{\rm{v}}} - \frac{1}{{\rm{u}}} = \frac{1}{{\rm{f}}}\)
- \(\frac{1}{{\rm{v}}} - \frac{1}{{\rm{-30}}} = \frac{1}{{\rm{10}}}\)
- v = 15 cm