It is 0.426 radians.
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It spells "critical" correctly
hi the critical angle is when the light comes in and it reflects
A critical angle refers to the highest angle the light can possibly refract into or between objects without disappearing. ie = light going from crystal into water, the critical angle is 47degrees.
The critical angle is not the same thing as the angle of incidence. There is a reason the confusion. The critical angle is defined as the smallest angle of incidence which results in total internal reflection. Every plane wave incident on a flat surface has an angle of incidence. That can be any angle. When a wave travels from a dense medium to a less dense medium, there comes an angle of incidence where there is no transmission into the less dense medium. We say then that for an angle of incidence above the "critical angle" the result is total internal reflection. It is also true that with Snell's law, the critical angle is the particular angle of incidence which would result in a 90 degree angle of refraction.
The critical angle is the angle where the wave is refracted at 90 degrees. Using Snell's law, nisinxi=nrsinxr, the two indexes of refraction, and the definition of a critical angle, it's pretty easy to figure out. Keep in mind that the critical angle ONLY occurs when the wave is travelling from a denser medium to a less dense medium (eg diamond to air) as angles formed when travelling into less dense mediums turn away from the normal, whereas if the opposite were to occur, even with an angle of incidence of 90 degrees, the angle of refraction would be less than 90 (it would turn towards the normal). The denser the medium, the larger its index of refraction value. knowing this, the equation would look something like: (larger n)sin(critical angle)=(smaller n)sin(90 degrees) Where you would input the known values and solve for the critical angle. Another tip is that sin(90 degrees) is just 1 so you could even just ignore that variable.