Electromagnetic signals questions

[dervast]

Hi i have noticed that some times we can denote an electromagnetic signal using cos os some timew we can write it in exponential form? Is that true? How can we convert from one type to the other?
For example i think that the signal Acos(wt-kr) it can be written to Ae^i(wt-kr)

Thx a lot

 

[Meir Achuz]

Usually, the physical result from complex notion is to take the real part,
so what you have written is correct. Keep the complex notation until you want to write down the predicted physical measuement.
The relation is e^{ix}=\cos x +i\sin x.

 

[dervast]

so when i write Acos(wt-kr) i forget to write the imaginary part right? Dont we lose information in that way? What the real part means (is used for) and what the imaginary one..
Thx a lot

 

[Meir Achuz]

The I am part is useful for intermediate calculations, but a final physical answer is always just the real part. For Quantum, the physical answer is always bilinear, like \psi^* \psi, which is real.

 

[dervast]

Thx a lot and what intermediate calculations are?

 

[Meir Achuz]

Thx a lot and what intermediate calculations are?

I just mean the steps between the beginning and the final answer.