Friday, 5 October 2018




spherical mirrors



Materials required: Rubber foam piece, slipper sole, Pins

Procedure: To understand convergent rays and divergent rays from mirror, we need to take a small piece of rubber foam and draw a straight line. Put the pins along the line drawn, and appears as straight lines coming out from the foam, now bend the piece of rubber foam inwards, and then we can observe that the pins meet at a point, and now bend the rubber foam, outwards then the pins appear that they are moving away from each other.

Conclusions:  Convergent rays meet to a point and divergent rays move away from each other.  The experiment also help us to understand the concept of normals to the curved surfaces, in the first case, the pins act as normals to the concave mirror and in the second case, the pins move away from a point.  The distance between converged or diverged point to surface is called Radius of curvature and the line is called normal.   



AIM: To find the focal length of a given concave mirror.

Materials required : Concave mirror, Screen, V-Stand (holder),                                          meter scale

Procedure: Collect the required materials from your laboratory, take V-stand and place the concave mirror in V-Stand, and to find the focal length of the concave mirror, we can use sun or tree or a person at a distance can be chosen as an object.  If you suppose sun as the object, then face the reflecting surface towards sun, and observe the clear image of the sun as a smallest bright spot on the screen or white paper, if you suppose tree as an object, then face the reflecting surface of the mirror towards the tree and observe an inverted image of the tree on the screen or a white paper.  

                 The distance from the image to the pole of the mirror is known as focal length of the mirror.  This distance is the distance between image and mirror as observed practically.

                We can observe the variation in size of the image when we move the screen towards or away from the Focus.

Precautions: Measure the distance accurately, look at the size of the screen or white paper which should not obstruct incoming sun rays.


AIM: To find the focal length of the given convex lens

Materials required: Convex lens, V-stand, screen, candle,                                              meter scale


                       Collect apparatus or materials required from laboratory, place the convex lens in v-stand, and place the screen on one side of the lens, and allow the light rays coming from distant object such as a tree.  Adjust the distance from the screen to the lens such that the image of the tree should be clear.  The distance from the image to the optic center of the lens is called the focal length of the lens.  

Precautions: screen, lens should be on the same line.


Focal length can be also called as minimum limiting object distance. 


AIM: To understand the change in focal length of lens with surrounding medium

Materials required: Convex lens, Circular lens holder, glass tumbler, Black stone


Before doing the experiment, find out the focal length of the given convex lens using distant object method, and note down the value.  Use the same lens and place in a lens holder.  Place a black stone at the bottom in glass tumbler which is filled with water.  Now slowly, place the lens holder with lens into the water, to see the clear image of the black stone.  The distance from the black stone to the lens will become the focal length of the lens.  

Precautions: Place the lens holder slowly into the water, the length of the tumbler should be at least 5 times than that of the focal length of the lens.  

Result & Observations:

We observe that the focal length of the convex lens is increased when it is placed in water.  We understand that the focal length depends on surrounding medium of the lens also.


AIM: To calculate/find the Least distance of distinct vision of eye

Materials required: 30 cm scale, Any printed material(news paper, textbook), observer


To identify the least distance of distinct vision of eye, read a text book or news paper, at certain distance from your eye.  Now you are able to read the contents from the book or paper, now you try to move the book or paper towards your eye till the contents are unable to read by you.  Then you try to increase the distance from your eyes till you get clear/clarity of the letters.  Ask your friend to measure the distance between your eyes and the book, this distance will be the least distance of the distinct vision of your eyes. Check the distance frequently, you can understand that whether there is any eye defect or not.


Hold the book properly, measure the distances accurately.


Least distance of distinct vision can be varied with age.


AIM: To understand dispersion of light - splitting of white light ray into seven colours

Materials required: Prism, Source of white light, [a dark room], a screen

Procedure .....The splitting of white light ray into its constituent colours is known as dispersion.  To do this activity, take a prism and white light source and allow the white light to pass through the prism, then we get seven colours called VIBGYOR.

Precautions: To get a narrow beam of light, white light should be allowed to pass through a small hole of paper or wooden plank.

Observations: When white light passes through a prism, dispersion takes place and refraction can be observed.  

The angle of deviation is different for different colours.  Violet is deviated maximum and red is deviated least. 


AIM: To prove white light is constituent of seven colors.

MATERIALS REQUIRED: Plane mirror, sunlight from sun, small tub with water


Take small tub and fill it with water, place the plane mirror in water such that it makes some angle with water surface and make it in the presence of sunlight, the water droplets act as prism and makes the white light into seven colors and these are reflected from the mirror and arrange the reflected light to fall on to the white wall.  One can observe the formation of rainbow.  

precautions to be taken:

1. arrange the demonstration under the presence of sun light.
2. the mirror should be at certain angle to the surface of water


-white light is constituent of seven colors (VIBGYOR).


  1. When I was in school, experiments in physics was my favorite part to do especially experiments on mirrors and lens but I do not like to do experiments on the dispersion of light. Each and every experiment has its own importance and you have done a great job by providing these 6 important experiments in detail. Keep doing it!

  2. thank you, you can expect more...