A light wave has a frequency of 6 x 1014 Hz. A) What is its period? B) What is its wavelength in a vacuum? C) When the light wave enters water, its velocity decreases to 0.75 times its velocity in vacuum. What happens to the frequency and wavelength?
c = λf
v = c/n
T = 1/f
The Attempt at a Solution
I understood how to do parts A and B.
For A, since we know the frequency, we can take the equation for period, T to find the answer:
T = 1/f = 1/(6 x 1014 Hz = 1.67 x 10-15 sec.
For B, we know that c = 3.0 x 108 m/s in a vacuum and we're given the frequency so wavelength is found by taking the equation:
λ = c/f = (3.0 x 108 m/s)/(6 x 1014 Hz) = 5 x 10-7 m.
For part C, however, I got confused.
I believe we can use the equation:
v = c/n
We're told that velocity decreases by 0.75 times in a vacuum so I think that v then would be:
v = 0.75c
So from here, we have to relate it to the equation c = λf.
So would we use the equation:
0.75c = λf to find wavelength since we already what f is? Can we assume that f does not change but that wavelength would?
To get wavelength then, we'd take:
0.75c/f = λ?