Sum of 2 EM Waves w/ Same Phase & Amp but Diff Freq

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fluidistic
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Homework Statement


Describe the sum of two EM waves that have the same initial phase and same amplitude but different frequencies such that [tex]\omega _1 >> \omega _2[/tex].

Homework Equations


[tex]E=E_0 \cos (kx -\omega t + \alpha)[/tex].

The Attempt at a Solution


I summed them up and reached, after an approximation, that [tex]E_1+E_2 \approx 2 E_0 \cos \left (kx -\frac{\omega _1t}{2} + \alpha \right ) \cos \left ( \frac{\omega _ 1 t}{2} \right )[/tex]. I don't know how to simplify further. It seems that the amplitude is the sum of both amplitudes and I'm not sure yet what is the frequency. It should be almost [tex]\omega _1[/tex], intuitively. I just don't know how to show it.
Any help is appreciated.
 
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Did you consider the fact that
[tex]k=\frac{\omega}{c}[/tex]
and that's why k is different for the two plane waves with two different frequencies?
 
physicsworks said:
Did you consider the fact that
[tex]k=\frac{\omega}{c}[/tex]
and that's why k is different for the two plane waves with two different frequencies?

Thanks, actually I didn't consider this. I will redo the exercise.