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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 5b

A light beam travels at 1.94 × 108 m/s in quartz. The wavelength of the light in quartz is 355 nm. If this same light travels through air, what is its wavelength there?

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1
First, understand that the speed of light in a medium is given by the equation: v = c/n, where c is the speed of light in vacuum (approximately 3.00 × 108 m/s) and n is the refractive index of the medium.
Calculate the refractive index of quartz using the given speed of light in quartz: n = c/v. Substitute v = 1.94 × 108 m/s and c = 3.00 × 108 m/s.
Once you have the refractive index of quartz, use the relationship between wavelength and refractive index: λmedium = λvacuum/n. Here, λmedium is the wavelength in quartz, which is given as 355 nm.
To find the wavelength of light in air, note that the refractive index of air is approximately 1. Therefore, the wavelength in air is approximately equal to the wavelength in vacuum.
Use the relationship λvacuum = λmedium × n to calculate the wavelength in air, substituting n = 1 and λmedium = 355 nm.

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Key Concepts

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

Speed of Light in Different Mediums

The speed of light varies depending on the medium it travels through due to the medium's refractive index. In a vacuum, light travels at approximately 3.00 x 10^8 m/s, but in materials like quartz, it slows down. Understanding how the refractive index affects light speed is crucial for calculating changes in wavelength when light transitions between mediums.
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Wavelength and Frequency Relationship

The wavelength of light is inversely proportional to its frequency, given by the equation c = λν, where c is the speed of light, λ is the wavelength, and ν is the frequency. When light moves from one medium to another, its speed and wavelength change, but its frequency remains constant. This relationship helps determine the new wavelength when light enters a different medium.
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Refractive Index

The refractive index of a medium quantifies how much light slows down compared to its speed in a vacuum. It is defined 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 calculate the speed and wavelength of light in different materials, essential for solving problems involving light transition between mediums.
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