i) Draw an arrow of length 4 cm using a black sketch pen on a thick sheet of paper.
ii) Take an empty cylindrical - shaped transparent vessel such as glass tumbler.
iii) Keep it on the table and ask your friend to bring the sheet of paper on which arrow was drawn behind the vessel while you look at it from the other side.
iv) When the vessel is empty, light from the arrow refracted at the curved interface, moves through the glass and enters into air than it again undergoes refraction on the opposite curved surface of the vessel and comes out into the air.
v) In this way light travels through two media and comes out of the vessel and forms a diminished image.
vi) Ask your friend to fill the vessel with water. Look at the figure of arrow from the same position as before.
vii) In this case, light enters the curved surface, moves through water, comes out of the glass and forms an virtual image.