(a) The light is a electromagnetic wave. The frequency of a wave is given by:
[tex]f=\frac{v}{\lambda}[/tex]
Where v is the speed of the wave and [tex]\lambda[/tex] its wavalength. In this case, v is the speed of light c.
[tex]f=\frac{c}{\lambda}\\f=\frac{3*10^8\frac{m}{s}}{489*10^{-9}m}\\f=6.21*10^{14}Hz[/tex]
(b) The wavelength of light in glass is defined as:
[tex]\lambda_g=\frac{\lambda_a}{n}\\\lambda_g=\frac{(483*10^{-9}m)}{1.52}\\\lambda_g=3.18*10^{-7}m[/tex]
(c) According to the first equation, the speed of the light in this glass is:
[tex]v=f\lambda_g\\v=6.21*10^{14}Hz*3.18*10^{-7}m\\v=1.97*10^{8}\frac{m}{s}[/tex]
