How To Work Out The Critical Angle Of A Substance: 4 Steps

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Last Updated: June 14, 2024

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wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, volunteer authors worked to edit and improve it over time. This article has been viewed 30,981 times.

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

1. 1 Make sure you know the Snell's Law. The general form of Snell's Law is nxsinθx=nvacuumsinθvacuum, where n is the refractive index and θ is the angle of incidence or refraction.
2. 2 Find out the refractive index of the substance (or nx). Advertisement
3. 3 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°.
   • nglasssinθglass=nvacuumsinθvacuum
   • 1.50sinθglass=1sin90°
   • sinθglass=2/3
   • θglass=41.8° (correct to 3 significant figures)
4. 4 The critical angle is therefore 41.8°. Advertisement

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• Question What is the value of sin42? Anika Shenoy Community Answer Assuming 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. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 1 Helpful 4

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Tips

• Remember than sin90° = 1. Thanks Helpful 4 Not Helpful 2
• You can always remember the formula for the critical angle instead. c=sin-1(1/nx) Thanks Helpful 4 Not Helpful 3
• Remember to add the '°' sign! Thanks Helpful 3 Not Helpful 3

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wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, volunteer authors worked to edit and improve it over time. This article has been viewed 30,981 times. 36 votes - 75% Co-authors: 8 Updated: June 14, 2024 Views: 30,981

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36 votes - 75% Click a star to vote Co-authors: 8 Updated: June 14, 2024 Views: 30,981

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