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 $v = \frac{c}{n}$, where $c$ is the speed of light in vacuum (approximately $3.00 \times 10^8$ m/s) and $n$ is the index of refraction of the medium. The plastic lens has a lower index of refraction (1.54) compared to the glass lens (1.65), which means light travels faster in the plastic lens. The speed of light in the plastic lens is $v = \frac{3.00 \times 10^8 \, \text{m/s}}{1.54} \approx 1.95 \times 10^8 \, \text{m/s}$.

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