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Ch 33: The Nature and Propagation of Light
Young & Freedman Calc - University Physics 14th Edition
Young & Freedman Calc14th EditionUniversity PhysicsISBN: 9780321973610Not the one you use?Change textbook
Chapter 33, Problem 9

Light traveling in air is incident on the surface of a block of plastic at an angle of 62.7° to the normal and is bent so that it makes a 48.1° angle with the normal in the plastic. Find the speed of light in the plastic.

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First, identify the known values: the angle of incidence (θ₁) is 62.7° and the angle of refraction (θ₂) is 48.1°. The speed of light in air (v₁) is approximately 3.00 x 10⁸ m/s.
Use Snell's Law to relate the angles and the indices of refraction: n₁ sin(θ₁) = n₂ sin(θ₂), where n₁ is the refractive index of air (approximately 1) and n₂ is the refractive index of the plastic.
Rearrange Snell's Law to solve for the refractive index of the plastic (n₂): n₂ = n₁ sin(θ₁) / sin(θ₂). Substitute the known values into this equation.
Once you have n₂, use the relationship between the speed of light in a medium and its refractive index: v₂ = v₁ / n₂, where v₂ is the speed of light in the plastic.
Substitute the values for v₁ and n₂ into the equation to find v₂, the speed of light in the plastic.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Snell's Law

Snell's Law describes how light bends when it passes from one medium to another. It is expressed as n1 * sin(θ1) = n2 * sin(θ2), where n1 and n2 are the refractive indices of the respective media, and θ1 and θ2 are the angles of incidence and refraction. This law is crucial for determining the refractive index of the plastic in this problem.
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Refractive Index

The refractive index of a medium is a measure of how much it reduces the speed of light compared to the speed of light in a vacuum. It is calculated as n = c/v, where c is the speed of light in a vacuum and v is the speed of light in the medium. Knowing the refractive index allows us to find the speed of light in the plastic.
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Speed of Light in a Medium

The speed of light in a medium is determined by the medium's refractive index. It is given by the formula v = c/n, where c is the speed of light in a vacuum (approximately 3.00 x 10^8 m/s) and n is the refractive index of the medium. This concept is essential for calculating the speed of light in the plastic once the refractive index is known.
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