The critical angle of a substance when passing a light ray from that substance to vacuum is very important as you must use it to determine whether total internal reflection will occur. It is also important for your physics test. Find out how to work out the critical angle!
Steps
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Make sure you know the Snell's Law. The general form of Snell's Law is n x sinθ x =n vacuum sinθ vacuum , where n is the refractive index and θ is the angle of incidence or refraction.
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Find out the refractive index of the substance (or n x ).Advertisement
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You can now do the substitution. Let's say you are using glass with a refractive index of 1.50. Therefore, the critical angle is the angle which, when it is the angle of incidence, produces an emergent ray of 90°.
- n glass sinθ glass =n vacuum sinθ vacuum
- 1.50sinθ glass =1sin90°
- sinθ glass =2/3
- θ glass =41.8° (correct to 3 significant figures)
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The critical angle is therefore 41.8°.Advertisement
Community Q&A
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QuestionWhat is the value of sin42?Anika ShenoyCommunity AnswerAssuming 42 radians, sin42 is 5.37. Assuming 42 degrees, sin42 is 0.67. You can find both by plugging it into a calculator set to the appropriate radian/degree mode.
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Video
Tips
- Remember than sin90° = 1.Thanks
- You can always remember the formula for the critical angle instead. c=sin -1 (1/n x )Thanks
- Remember to add the '°' sign!Thanks
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Things You'll Need
- Paper
- Calculator
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