9. Complete Activity 11.9 (Page 133). Take a convex lens or magnifying glass. Put it in the path of sunrays. Place a sheet of paper as shown. Adjust the distance between the lens and the paper till you get a bright spot on the paper. Hold the lens and the paper in this position for a few minutes. Does the paper begin to burn?
Now replace the convex lens with a concave lens. Do you see a bright spot on the paper this time too? Why are you now getting a bright spot this time?
Answer:
The activity can be carried out as follows:
Aim: To examine if a bright spot on paper can be obtained by placing a convex and a concave lens under the sun and make the necessary conclusions.
Materials Required: Convex lens, concave lens, white paper sheet,
Procedure:
Part 1:
(i) Take a convex lens or magnifying glass and place it in the path of sunrays out in the open.
(ii) Place a sheet of paper on the ground.
(iii) Adjust the distance between the lens and the paper till you get a sharp bright spot on the paper. Hold the lens and the paper in this position for a few minutes and observe what happens.
Part 2:
(i) Take a concave lens and place it in the path of sunrays out in the open.
(ii) Place a sheet of paper on the ground.
(iii) Try to get a sharp bright spot on the paper using the lens.
Observations:
Part 1: For the convex lens you will see a focused bright spot on the paper and after a few minutes that part will start burning as shown below.
Part 2: For the concave lens you will not be able to get a focused bright spot on the paper as shown below.
Conclusions: We conclude that:
- You can get a bright spot using a convex lens, hence it converges light and is called a converging lens.
- You cannot get a bright spot using a concave lens, hence it diverges light and is called a diverging lens.
Related Links:
Solution to Extended Learning Problem 1
Solution to Extended Learning Problem 2
Solution to Extended Learning Problem 3
Solution to Extended Learning Problem 4
Solution to Extended Learning Problem 5
Solution to Extended Learning Problem 6
Solution to Activity 11.1
Solution to Activity 11.2
Solution to Activity 11.3
Solution to Activity 11.4
Solution to Activity 11.5
Solution to Activity 11.6
Solution to Activity 11.7
Solution to Activity 11.8
Solution to Activity 11.9
Solution to Activity 11.10
Solution to Activity 11.11
Solution to Activity 11.12
