Question

Explain with the help of a ray diagram, why a pencil partly immersed in water appears to be bent at the water surface.

Answer 1

A stick or a pencil half immersed in water at an angle appears bent due to refraction of light at the air-water surface. Figure shows a straight stick AO whose lower portion BO is immersed in water. It appears to be bent at point B in the direction BI. A ray of light OC coming from the lower end C) passes from water into the air at C and gets refracted away from the normal in the direction CX. Another ray OD gets refracted in the direction DY. The two refracted ray CX and DY, when produced backward, appear to meet at point I, nearer to the water surface than O. Similarly each part of the immersed portion of the stick raised. As a result immersed portion of the stick appears to be bent when viewed at an angle from outside.

Answer 2

ABC is a pencil immersed partially in water. Rays of light starting from A suffer refraction at the water surface XY, bend away from normal and appear to come from A'. Therefore, the pencil ABC appears as A'BC, bent at the water surface at B.