# Homework Help: Where did I go wrong?

1. Nov 28, 2005

### lw11011

What is the wavelength, k, corresponding to a frequency, w, of 7x10^19 Hz of electromagnetic wave in free space? The speed of light is 2.99792x10^8 m/s. Answer in units of m.
I set w/k=c
Plugging in (2*pi*7X10^19) for w, and 2.99792x10^8 for c, I got 1.467X10^12. The answer is wrong. Where did I go wrong?

2. Nov 28, 2005

### Staff: Mentor

For one thing, the wave equation is $c = f \lambda$. The frequency is in given in Hz; the wavelength (not wave number) has units of meters.

PS: Don't confuse wavelength with the wave number (k), which is generally defined as $k = 2 \pi / \lambda$. If you want the wave number, then using $k = \omega / c$ will work.

Last edited: Nov 28, 2005