Every time it tries to leave it is reflected back inside. Optical fibres Light is refracted as it enters the fibre. This idea is used in reflective clothes and signs. Two of these prisms can be used to produce a periscope.īack the way they came A right angled prism will also bend light through 180. Using TIR A right angled prism will bend light through 90. The greater the refractive index, the smaller the critical angle. It can be calculated using the following formula: Sin c = 1/n Where: n = Refractive index, c = Critical angle at which TIR first occurs.Ĭritical angle – Example 1 Calculate the critical angle for a glass block of refractive index 1.45 sin (c) = 1 / n sin (c) = 1 / 1.45 sin (c) = 0.69 c = 44ºĬritical angle – Example 2 Calculate the refractive index of a material where TIR occurs at a critical angle of 37º sin (c) = 1 / n n = 1 / sin (c) n = 1 / sin (37) n = 1 / 0.60 n = 1.66 11 The higher the refractive index, the lower the critical angle. Critical caseĬritical calculations The critical angle for a material depends upon the refractive index. Diamond has the lowest at 24°, which is why it reflects so much light. Total internal reflection (TIR) Different materials have different critical angles. The angle at which total internal reflection first occurs is called thecritical ic This angle is called the critical angle ( c). This effect is called Total Internal Reflection and can occur in many different materials. What happens to the light? Well the light is reflected back inside the material. No more than ninety degrees As soon as the angle of refraction reaches 90, the light can no longer be refracted. When light passing out of the glass block its angle increases To understand the difference between analogue and digital signals.To describe the role of total internal reflection in transmitting information along optical fibres and in prisms.To recall and use the relationship between critical angle and refractive index: sin c = 1/n.To recall the meaning of critical angle c.
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