To understand that different set of rays form different images.
The textbook formula of real depth /apparent depth = refractive constant suggests that the image of the object placed at the bottom of a transparent solid or liquid is somewhat above the object. But this equation is valid only if the viewer is above the object. This means, only to the rays nearly normal to the surface should be used if the above equation is to be used. This experiment is designed to bring out this fact.
Refraction of light, image formation.
A large size petric dish or any vessel with small height and large diameter, a coin and water.
- Place the dish on a table and place the cap at the center of the dish
- Ask a friend sitting at large distance “where is the cap”. He/She will see it at the center of the dish.
- Now fill water in the dish and ask the friend “where is the cap”. The friend will feel that you have shifted the cap towards the farther wall.
- Remove water from the dish using a dropper or syringe while the friend is seeing the operation.
- Ask him where is the cap. He/She will see it at the center.
As the dish is of small height, the friend is receiving the rays making large angle with the normal. The image is formed not only above the object, but also is shifted horizontally as shown in the figure. As the dish is shallow, the height shifted in not much visible but horizontal shift is quite significant.