Question

In the series RLC circuit of problem 1 the resistor is replaced with the higher available value of 68 KOhm. The circuit is driven in forced oscillation regime up to a frequency of 200 KHz. A resonance is observed at a frequency of the order of 160 KHz. How would you explain this result? What combinations of capacitor / inductor values would produce a resonance at that frequency, and what parts of the setup are possible candidates for effective reactance elements at that frequency?

Answer 1

The resonance of a series RLC circuit occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are 180 degrees apart in phase. The sharp minimum in impedance which occurs is useful in tuning applications. The sharpness of the minimum depends on the value of R and is characterized by the "Q" of the circuit.

The selectivity of a circuit is dependent upon the amount of resistance in the circuit. The variations on a series resonant circuit at right follow an example in Serway & Beichner. The smaller the resistance, the higher the "Q" for given values of L and C. The parallel resonant circuit is more commonly used in electronics, but the algebra necessary to characterize the resonance is much more involved.

if the value of resistance increased the impedence

we know

at resonance frquency

so Z=R=

Now for greater the value of resistance the frequency range is higherv than orevious

resonace frequency

lower and uper frequency are

we get

Henri.Farade

the reactive element =