When a pencil is put in a glass of water, it would appear bent because of refraction of light. Refraction is the bending of light as it passes from one transparent substance into another. Light waves can’t travel as quickly in water as it does in the air. Hence they bend around the pencil, causing the pencil to look bent in the water. Further, the light refraction gives the pencil a slight magnifying effect, which makes the angle appear bigger, causing the pencil to look bent. It all has to do with the fact that light travels more slowly in water than it does in air, and that causes the light to bend when it goes from water to air, or vice versa. How the light bends depends on the shape of the water surface and the angle at which the light hits it.
It is the same “magnifying lens” phenomenon that makes things look fatter when viewed through a glass of water. In that case, the fattening effect is doubled, because the beam of light widens both when it enters the water through a curved surface and when it leaves through the other side.
Credit : Orlando sentinel
Picture Credit : Google
