# Wavelength, period of vibration in seconds

1. Feb 17, 2015

### Rick2015

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >

Okay, I am having trouble with the units. I have the values for the wavenumber and I am trying to find the period.
These are the formulas that I am trying.
T = 1/f ; f = c/lambda

example: lambda = 3657 cm^-1 ; c = 2.998 x 10^8 m/s
I am doing 2.998 x 10^8 m/s / (3657 cm^1 x (1 cm/0.01m))
however, the unit for frequency is Hz = 1/s
I am getting m^2 on the denominator.
Am I using the right formulas?
thanks!

Last edited by a moderator: Feb 17, 2015
2. Feb 17, 2015

### Staff: Mentor

By wavenumber, do you mean wavelength? If so, wavelength has units of meters, not 1/meters.

3. Feb 17, 2015

### Rick2015

yes. it is the wavelength. But I am getting m^2

4. Feb 17, 2015

### Staff: Mentor

So you are given the wavelength, and want to find the period? Start off with the conversion equation that makes sense in terms of units...

$$Period = \frac{Wavelength [m]}{Velocity [\frac{m}{s}]}$$

5. Feb 17, 2015

### Staff: Mentor

A wavelength has units of meters, not inverse meters.
Inverse meters suggest it is a wavenumber (usually called "k"). You can convert it to a wavelength, or directly use formulas with the wavenumber.

6. Feb 17, 2015

### Staff: Mentor

Not sure why my Latex isn't rendering correctly. It previews fine. Oh well, the old fashioned way:

Period [in seconds] = Wavelength [in meters] / Velocity [in meters/second]

EDIT -- I see now that using [ s ] without the spaces caused a strikethrough... Duh.

7. Feb 17, 2015

### Rick2015

I got it! Thank you!