Q:

Frequency Response RLC circuit - Current against Frequency graph - Symmetry?

I understand that in a Frequency Response experiment dealing with an RLC circuit, the graph of Current against Frequency is supposed to be symmetrical about the resonant frequency theoretically.
However, experimentally it is not the case.
Could anyone explain why this happens?

A:

For a series LRC circuit, the magnitude of the current is indeed symmetrical about the resonant frequency, if you plot the frequency on a logarithmic scale.
$$\left| Z \right| = \sqrt{R^2 +\frac{L}{C} \left[ \frac{\omega}{\omega_0}-\frac{\omega_0}{\omega}\right]^2}$$
where the resonant angular frequency $\omega_0$ is just 
$$\omega_0 = \frac{1}{\sqrt{L C}} $$
so 
$$ \left|Z \left(\frac{\omega}{\omega_0} \right) \right|=\left|Z \left(\frac{\omega_0}{\omega} \right) \right| $$
Since the magnitude of the current is the applied voltage divided by $|Z|$, for a constant applied voltage (e.g. magnitude of voltage frequency-independent), the result follows.
The phase is anti-symmetric, in the same sense.

