Skip to main content

Class 8, Science, Chapter-13, Lecture-2, Image (Notes)

IMAGE:

A point where a number of light rays coming from a point source actually meet or appear to meet after reflection or refraction is termed as the image of the point source.

REAL IMAGE:

A point where a number of light rays coming from a point source actually meet after reflection or refraction is termed as a real image of the point source.

VIRTUAL IMAGE:

A point where a number of light rays coming from a point source do not actually meet but appear to meet after reflection or refraction is termed as a virtual image of the point source.

DIFFERENCES BETWEEN:

REAL IMAGE

VIRTUAL IMAGE

A real image is formed by actual intersection of rays.

A virtual image is not formed by actual intersection of rays.

It can be obtained on a screen.

It cannot be obtained on a screen.

It is always inverted.

It is always erect.

CHARACTERISTICS OF IMAGE FORMED BY A PLANE MIRROR:

The image formed by a plane mirror is

  1. virtual and erect.
  2. of the same size as the object.
  3. as far behind the mirror as the object is in front of the mirror.
  4. laterally inverted.

PERISCOPE: 

A long, tubular device which works on the reflection of light from two plane mirrors arranged parallel to one another and enables us to see objects that are out of the line of sight is called a Periscope.

CONSTRUCTION:

A periscope consists of

  • A long tube with two holes on opposite sides
  • Plane mirror M1 fitted at the end of the tube making an angle of 45O with the side of the tube and facing the first hole
  • Plane mirror M2 fitted at the other end of the tube and parallel to mirror M1 and facing the second hole.

WORKING:

  • Light from an object (not in line of sight) falls on mirror M1 through the first hole.
  • Mirror M1 reflects the light to fall on the mirror M2.
  • Mirror M2 reflects the reflected light to the eye of the observer and makes the object visible.