Define the critical angle for total internal reflection.

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Multiple Choice

Define the critical angle for total internal reflection.

Explanation:
Total internal reflection happens when light travels from a medium with a higher refractive index to one with a lower index, and the incidence angle is large enough that the refracted ray would skim along the boundary. The critical angle is that threshold angle for which the refracted ray travels exactly along the interface, i.e., the refracted angle is 90 degrees. Using Snell’s law, n1 sin θ1 = n2 sin θ2. At the critical angle, θ2 = 90°, so sin θc = n2 / n1. Therefore θc = arcsin(n2 / n1). This only makes sense when n1 > n2, otherwise there is no critical angle and total internal reflection does not occur. The expression arcsin(n2 / n1) is the standard result.

Total internal reflection happens when light travels from a medium with a higher refractive index to one with a lower index, and the incidence angle is large enough that the refracted ray would skim along the boundary. The critical angle is that threshold angle for which the refracted ray travels exactly along the interface, i.e., the refracted angle is 90 degrees.

Using Snell’s law, n1 sin θ1 = n2 sin θ2. At the critical angle, θ2 = 90°, so sin θc = n2 / n1. Therefore θc = arcsin(n2 / n1). This only makes sense when n1 > n2, otherwise there is no critical angle and total internal reflection does not occur. The expression arcsin(n2 / n1) is the standard result.

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