Hi i am just finishing off one the last assignments of the year and have got stuck with this question:

A series circuit consists of a coil of inductance 0.1H and resistance 25Ω and a variable capacitor. A voltage is applied to the circuit. The instantaneous value of voltage is given by

v = 100sin ωt + 20 sin (3ωt + 45°) + 5 sin (5ωt - 30°) Volts

Identify the harmonics present in the voltage if ω=314 rad s⁻¹

Am i correct in believing that it is simply asking for the source of the harmonics?

 

What do you mean by the 'source' of the harmonics? The physical source (inductor/cap) or the mathematical terms contributing to the harmonics and their values?
It looks pretty straightforward, you need to answer what multiples of the fundamental are present in the output.

 

Yes, i meant physical source. I wasn't sure if i was being asked what was causing the harmonics or what ones are present.

I see now that the 3rd and 5th are present. The answer seems to straight forward.

 

If you aren't given the value of the variable capacitor, then you can't determine the magnitudes of anything that involves the response of the circuit. But since you aren't asked to, this is irrelevant. You are give an expression for a voltage signal and asked to identify the harmonics in that signal. It doesn't matter what circuit is involved, you are given the voltage explicitly.