A student focused the image of a distant object using a device X on a white screen S as shown in the figure. If the distance of the screen from the device is 30 cm, select the correct statement about the device X.

In the preparation of soap, a small amount of sodium chloride(common salt) is added to the mixture of fat and sodium hydroxide. The role of common salt is to

A student takes about 6 ml distilled water in four test tubes marked P, Q R and S. He dissolves sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R and magnesium sulphate in S. After that he adds equal amount of soap solution in each test tube. On shaking these test tubes, he would observe a good amount of lather in the test tubes marked

A student traces the path of a ray of light through a rectangular glass slab for four different angles of incidence. He very cautiously measures the angle i, angle rand the angle e. on analyzing his measurements, he is likely to draw the following conclusion:

For the refraction of a ray of light through a glass prism, the path of a ray of light is

Shown below:

The angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by