# Wavelength / Frequency notation!

1. Jan 19, 2009

### fasa

http://en.wikipedia.org/wiki/Electromagnetic_waves

Please navigate to this link about electromagnetic waves. Scroll down a little you will see a drawing on left hand side under topic "Properties" which denotes electric and magnetic field components of light as an example of an electromagnetic wave.

Now lets examine this drawing. According to the letter "E" we understand that vertical axis denotes Amplitude of Electric field component and according to letter "M" we understand that the axis perpendicular to the screen right you are looking at now denotes Amplitude of Magnetic field component of the electromagnetic wave.

The point where i confused is when letter "lambda" mesures the distance between to following peaks. If this distance is Wavelength, it means that the horizontal axis must be in units of cm., mm., or km. ...

Ok lets accept it. Then please help me to understand where will i measure Frequency? Because when denoting frequency of a wave, horizontal axis is time domain. But i don't understand that how the shape remains same although we just change the domain what horizontal axis denotes.

2. Jan 19, 2009

### Staff: Mentor

The graph of E is a "snapshot" of the moving wave at a particular instant of time. You start with the function

$$E = E_0 \sin (kx - \omega t)$$

where $k = 2\pi / \lambda$ and $\omega = 2\pi f$. Then you choose a particular value of t and make a graph of E versus x.

If instead, you choose a particular value of x, and make a graph of E versus t, you get a graph that shows how one point on the wave oscillates with time. The horizontal "distance" (time interval) between two peaks is the period, T, and the frequency is f = 1/T.

3. Jan 21, 2009

thank you.