English: A pencil when partially submerged in a glass of water appears to be bent. In this picture there are three different optical mediums ( 1.air, 2.glass, 3.water).The bending is actually observed in two mediums i.e, glass and water due to refraction of light. Refraction occurs first at the glass-air interface and then at the water-glass interface. Here, the pencil appears to be bent more in glass than in water because glass has higher refractive index as compared to water and it's also optically denser than water.