12/17/2023 0 Comments Total internal reflection in prism![]() ![]() As the critical angle for glass is 42 o, the light ray hitting the glass prism at an angle of 45 o will be totally internally reflected.Ī second prism can be placed so that the ray emerging from the first prism, travels directly into the second prism and the process of total internal reflection continues. The light continues to travel until it strikes the surface between A and C at an angle of 45 o. The ray of light is reflected back at an equal angle of 45 o and hits the edge of the prism between B and C where it again is reflected out at an angle of 45 o. ![]() To do this on your calculator press the shift key and then the sin button to get sin -1.Īs the diagram shows, the incident ray enters the prism below A and hits the back edge of the prism between A and B at an angle of 45 o. To convert this into the critical angle, you need to remove the sin function. ![]() Using our previously calculated value for the refractive index of 1.27 for the Perspex block, we can now calculate the critical angle as follows: Where sin ( c) is the critical angle and n is the refractive index of the medium. This relationship is shown by the equation: There is a relationship between the refractive index of the medium being used and the critical angle above which total internal reflection will occur. If the less dense material is air, then the critical angle of glass is usually 42 o, and 49 o for water. The critical angle will depend on the media that is on either side of the boundary. As the angle used is above the critical angle, all of the light is reflected back into the block at the same angle and no refraction occurs. The incident ray will hit the glass block at an angle above 42 o. A light box is used to direct a ray of light through the centre of the block from the curved side. You can investigate total internal reflection using a semi-circular glass block as shown in the diagram above. ![]()
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