Frequency of Light in a Solid

[Mohji]

Homework Statement

A light wave has a 678 nm wavelength in air. Its wavelength in a transparent solid is 493 nm.

a) What is the speed of light in this solid?
b) What is the light's frequency in the solid?

Homework Equations

v = λf

The Attempt at a Solution

a) I got the correct answer for this one. Let v1 and λ1 be speed of light and wavelength in air, v2 and λ2 in solid.

v1 = λ1f
f = v1 / λ1
f = (3.00e8 m/s) / (6.78e-9 m)
f = 4.42e16 Hz

v2 = λ2f
v2 = (4.93e-9 m) (4.42e16 Hz)
v2 = 2.18e8 m/s

This is the correct answer.

b) I was under the impression that the frequency of light does not change from one medium to another, meaning it would still be 4.42e16 Hz. This is the principle that I used to solve a). However, the online assignment keeps telling me that the answer is incorrect.

Am I making a mistake here? Any help would be greatly appreciated.

 

[ehild]

v1 = λ1f
f = v1 / λ1
f = (3.00e8 m/s) / (6.78e-9 m)
f = 4.42e16 Hz

You made a mistake here, the wavelength 678 nm is 6.78 e-7 m, so your frequency is wrong.

And you are right, the frequency does not change when the light wave enters into an other medium.

ehild

 

[Mohji]

You made a mistake here, the wavelength 678 nm is 6.78 e-7 m, so your frequency is wrong.

And you are right, the frequency does not change when the light wave enters into an other medium.

ehild

D'oh! Always overlook the possibility of something small like a conversion error. Thanks a lot for the quick reply.