Blue light with a wavelength of 425 nm passes from a vacuum into a glass lens; and the index of refraction is found to be 1.65. The glass lens is replaced with a plastic lens. The index of refraction for the plastic lens is 1.54. In which one of the two lenses does the light have the greatest speed and what is that speed? A)glass, 2.28 × 10⁸ m/s B)plastic, 2.13 × 10⁸ m/s C)glass, 1.82 × 10⁸ m/s D)plastic, 1.95 × 10⁸ m/s E)The speed of the blue light is the same in the vacuum and both lenses; and it is 2.99 × 10⁸ m/s.

Question

Quizplus · Accepted Answer

The speed of light in a medium is given by v = c/n, where c is the speed of light in vacuum (approximately 3.00 × 10^8 m/s) and n is the index of refraction. For the plastic lens, v = 3.00 × 10^8 m/s / 1.54 = 1.95 × 10^8 m/s, which is greater than the speed in the glass lens.

Blue Light with a Wavelength of 425 Nm Passes from a Vacuum