H Exp – Radiation and Matter 06 – Critical angle of a perspex block

Aim – To measure the critical angle θc of a perspex block.

Instructions

▪ The angle θp of the ray of light to the normal in the Perspex block is 10^o. Turn on the protractor and measure the corresponding angle θa .
▪ Increase the angle θp in 5^o steps and in each case measure the angle of refraction θa
▪ When the angle of refraction θa gets large, the increase in angle is reduced to steps of 1^o
▪ Note the angle in the Perspex block at which the light is no longer refracted out of the block. This is the critical angle θc for the Perspex.