Class 10 Science Solutions English Medium

Image Formation by Lenses: 

Refracting the light from a lens after passing through an object the lens forms an image of the object. 

A. Nature of the Image: The image formed by a lens can either be real and inverted or be virtual and erect, these are called the nature of Image. 

Type of Nature of Images: 

(I) Real and Inverted : The image which can be shown on a screen is called real image and forming upside of an image down or in the opposite position is called inverted image. 

(II) Virtual and Erect: The image which can not be printed on a screen is called vertual image and Erect means upward in straight position. 

B. Position of the image: The place where the image forms is called the position of the image. Position is a vector quantity which may be negative or positive in magnitude. All positions in a lens is measured from optic centre. From where the light enters or the object is placed is measured as negative and where the light refracts is measured as positive. 

Position of the object: Where the object is placed is called the position of the object. It may be at infinity, beyond 2F1, between F1 and 2F1, at focus F1 and between F1 and optical centre. 

Position of the object always measured as negative because objects are placed where the light enters.  

C. Relative size of the image: There are various sizes of images formed by the lenses. It may be point size, highly diminished, diminished same size enlarged or highly enlarge. 

See the table: Nature, position and relative size of the image formed by a convex lens for various positions of the objects. 

Nature, position and relative size of the image formed by a concave lens for various positions of the objects. 

Image Formation in Lenses Using Ray Diagrams:

To understand the ray diagram we have to study the two rays;

(i) Ray passing through the object parallel to principal axis.

(ii) Ray passing through the object and optical centre. 

In convex lens: 

(i) A ray of light from the object, parallel to the principal axis, after refraction from a convex lens, passes through the principal focus on the other side of the lens. 

(ii) A ray of light passing through a principal focus, after refraction
from a convex lens, will emerge parallel to the principal axis.

(iii) A ray of light passing through the optical centre of a lens will
emerge without any deviation.

In Concave lens:

(i) A ray of light from the object, parallel to the principal axis, after
refraction from a concave lens, the ray appears to diverge from the principal focus located on the same side of the lens.

(ii) A ray of light appearing to meet at the principal focus of a concave lens, after refraction, will emerge parallel to the principal axis.

(iii) A ray of light passing through the optical centre of a lens will emerge without any deviation.