Important Equations 

Equations provided by Eric Weisstiens world 

Cirtical Angle 

Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.

When light crosses a boundary between materials with different refractive indices, the light beam will be partially refracted at the boundary surface, and partially reflected. However, if the angle of incidence is greater (i.e. the ray is closer to being parallel to the boundary) than the critical angle – the angle of incidence at which light is refracted such that it travels along the boundary – then the light will stop crossing the boundary altogether and instead be totally reflected back internally. This can only occur where light travels from a medium with a higher [n1=higher refractive index] to one with a lower refractive index[n2=lower refractive index]. For example, it will occur when passing from glass to air, but not when passing from air to glass.

Definition provided by Wikipedia




1. What is the critical angle of refraction for light rays going from water to glass?

2. What is the critical angle of refraction for light rays going from glycerine (n = 1.47) into air?

3. The critical angle of a ray of light is measured as 48.8 degrees as it goes from an unknown liquid into air. Find the index of refraction of the the liquid. Using the internet determine what that liquid is (this link maybe useful)