# Homework Help: Electromagnetic waves

1. Mar 6, 2010

### thereddevils

1. The problem statement, all variables and given/known data

The electric components E1 and E2 of two coherent electromagnetic waves are given as follows :

$$E_1=E_o\sin (\omega t-kx)$$

$$E_2=E_o\sin (\omega t-k(x+\delta))$$

These two waves superpose each other at a certain point . Derive the amplitude of the resultant wave in terms of k and delta .

2. Relevant equations

3. The attempt at a solution

I tried adding them using the sin formulas , but i failed to express it in the form of

$$A \cos \theta \sin \omega t$$

2. Mar 6, 2010

### ehild

The sum of the two waves can be substituted by a single one of the same angular frequency w and wavenumber k, that is

$$E_o\sin (\omega t-kx)+E_o\sin (\omega t-k(x+\delta))= A\sin (\omega t-k(x+\alpha))$$.

You have to find the expression of A in terms of E0 and delta.

ehild

3. Mar 6, 2010

### thereddevils

thanks ehild , but i don really get it , i don see where is the alpha coming from ..

4. Mar 6, 2010

### ehild

Alpha is a phase constant for the new wave. You can determine both alpha and the amplitude A by using the identity for the sine of the difference of angles. Have you learnt how to do it?

ehild

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