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Light - Reflection and Refraction

Terms used in a Spherical Mirror

Images formed by spherical mirrors

Spherical mirrors form images of an object that may be smaller, larger, or of the same size, erect or inverted, depending on their type and their distance from the object. In general, images formed by any type of mirrors can be classified in two types: real images and virtual images.

Difference between a real image and a virtual image

S. No.

Real Image

Virtual Image

1.

Can be obtained on a screen or wall

Cannot be obtained on a screen or wall

2.

Can be touched

Cannot be touched

3.

Formed in front of the mirror

Formed behind the mirror

4.

Formed by concave mirrors only

Formed by all types of mirrors i.e., plane, convex, and concave

5.

These images are always inverted

These images are always erect

You can distinguish between real and virtual images by checking the orientation (erect or inverted) of images and also by touching them.

Let us learn about the images formed by different spherical mirrors.


So, you have seen that

  • the image formed by a convex mirror is virtual, erect, and of a smaller size.
  • the image formed by a concave mirror is virtual, erect and of a larger size when placed near the surface of the mirror; and inverted and may be smaller or larger than the object when placed at a distance from the surface.

Concave mirrors form larger, smaller and of same size real images and also larger virtual images. On the other land, convex mirrors always form smaller virtual images.

Take a concave mirror and a sharpener. Now, try to see the image of the sharpener in the mirror. Make sure that the sharpener is at a large distance from the concave mirror. Observe the size and the orientation of the image. Now, reduce the distance between the sharpener and the mirror and again notice the size and the orientation of the image. Repeat the observation by reducing the distance and try to complete the following table.

Distance between the sharpener and the concave mirror

Size of the image

Character of the image

20 cm

Smaller

Inverted

15 cm

Equal

 

10 cm

   

5 cm

   

Replace the concave mirror with a convex mirror and follow the same steps. Make a similar table for the convex lens too.

Collect some objects that have shiny surfaces and classify them as plane, convex, or concave mirrors.

 

Reflection by Spherical Mirrors

The different ways in which a ray of light is reflected from a spherical mirror are as follows:

Case I: When the incident light ray is parallel to the principal axis

In this case, the reflected ray will pass through the focus of a concave mirror, or will appear to pass through the focus of a convex mirror.


Case II: When the incident light ray passes through the focus of a concave mirror, or appears to pass through the focus of a convex mirror

In this case, the reflected light will be parallel to the principal axis of the spherical mirror.

Case III: When the incident ray passes through or appears to pass through the centre of curvature

In this case, after reflecting from the spherical surface, light moves back in the same path. This…

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