# Wavelength/Frequency short Questions help

For a) I did frequency = speed of light / wavelength = 3.75x1014Hz
for b) I did 3.75x1014Hz x 10-15s=0.375
I think a) is right, but I don't know about b)
For c) I would have thought it is the same frequency as the first because I am taking it as if it is the same frequency, but a shorter amount of time, but I think this is wrong.

Help?

ideasrule
Homework Helper

For a) I did frequency = speed of light / wavelength = 3.75x1014Hz
for b) I did 3.75x1014Hz x 10-15s=0.375

10^-15 s is one femtosecond, not 20.

For c) I would have thought it is the same frequency as the first because I am taking it as if it is the same frequency, but a shorter amount of time, but I think this is wrong.

Have you tried the energy-time uncertainty principle?

Oh right, so I guess b) would be what I put times 20, so 7.5...
c) If that has anything to do with heisenberg's uncertainty principle, we haven't been taught that in this class, is there another way?

Or if I use that which equation should I use? I looked at it, but I'm not sure how it applies.

Hm I looked at the equations, and have found that $$1/2\delta T = 2.5x10^{13}hz$$ where delta T = 20 femtoseconds...is this correct?