Question

The wavelength of red helium-neon laser light in air is 632.8 nm.

Answer 1

(a) $4.74\cdot 10^14 Hz$

The frequency of an electromagnetic wave is given by:

$f=\frac{c}{\lambda}$

where

$c=3.0\cdot 10^8 m/s$ is the speed of the wave in a vacuum (speed of light)

$\lambda$ is the wavelength

In this problem, we have laser light with wavelength

$\lambda=632.8 nm=6.33\cdot 10^{-7} m$. Substituting into the formula, we find its frequency:

$f=\frac{3.0\cdot 10^8 m/s}{6.33\cdot 10^{-7} m}=4.74\cdot 10^14 Hz$

(b) 427.6 nm

The wavelength of an electromagnetic wave in a medium is given by:

$\lambda=\frac{\lambda_0}{n}$

where

$\lambda_0$ is the original wavelength in a vacuum (approximately equal to that in air)

$n$ is the index of refraction of the medium

In this problem, we have

$\lambda_0=632.8 nm$

n = 1.48 (index of refraction of glass)

Substituting into the formula,

$\lambda=\frac{632.8 nm}{1.48}=427.6 nm$

(c) $2.03\cdot 10^8 m/s$

The speed of an electromagnetic wave in a medium is

$v=\frac{c}{n}$

where c is the speed of light in a vacuum and n is the refractive index of the medium.

Since in this problem n=1.48, we find

$v=\frac{3\cdot 10^8 m/s}{1.48}=2.03\cdot 10^8 m/s$