Can somebody please help me with this task?

Assumption:

- Emf = 100sin(2pi*ft) +30 sin(6pi*ft)

Whats the effective voltage?

 

Effective voltage ? Do you mean RMS voltage?
http://www.wolframalpha.com/input/?i=RMS+of+(100sin(2pi+*t)+++30+sin(6pi*t))+

 

Thanks for reply. Yes, that's the aswer I'm looking for

If you should do it by hand do you have to integrate from 0 to T ?

 

You can simply do it with the two amplitudes, square them, then do the mean, then root and you get the same number as wolfram.

Side note, how does that work with a single sine wave? Mean of 10000 is still 10000, so the rms would be 100, but wolfram says 70.7 so it obviously halved the square before doing the root, why? Is it like mean of 10000 + 0? That doesn´t really make sense as it could also be 10000 + 0 + 0 which would give a different value..?

 

OR simply solve this

\(\sqrt{\frac{1}{2\pi} \int_0^{2\pi} ( 100 Sin(2t) + 30 Sin(6t) )^2 \mathrm{d}t}\)

 

I would simply use the relationship that for a composite signal comprising N simple sinusoids each having RMS values V1, V2, ......VN then the equivalent RMS value is given by

\(V_{RMS}=\sqr{(V_1^2+V_2^2+......+V_N^2)}\)

The RMS value of a simple sinusoid of peak value Vp is (as we know) Vp/√2