Resonant Frequency

[karim102]

Hi,
I want to know why if XL = XC in circuit which has only capacitor and inductive. The current will be mixmum not infinity because we know the rule which I=V\Z which z is impedance. so the z will be zore so the current must be infinity.

 

[abdo375]

What you have done is that you have included the resistance in the analysis and that gave you a certain expression for the RLC circuit, but then you removed the resistance (set it to zero) and expected that the same expression would apply, to get the impedance of an LC circuit you must dervie from the circuit an expression of it's own.

 

[arunbg]

What you have done is that you have included the resistance in the analysis and that gave you a certain expression for the RLC circuit, but then you removed the resistance (set it to zero) and expected that the same expression would apply, to get the impedance of an LC circuit you must dervie from the circuit an expression of it's own.

The expression is still going to be the same even when derived individually
for an LC circuit or we let R tend to 0 in the expression for LCR circuit as the phasor diagram clearly suggests.

In theory the current must indeed rise to infinity.However in practice there is always a resistive element in the circuit (however small) and will probably overheat and short the circuit.
Alternately, the same is the case when the two ends of a battery are connected with no resistance in between.
As per Kischoff's law current in the circuit is infinite right ?
But this is not observed and we see that the wire just heats up.
Maybe if the wire was made of superconducting material we could argue the matter of an infinite current.

 

[abdo375]

Your absolutely right I don't know what the hell I was thinking when I wrote this answer.

 

[karim102]

you absolutely right. I see know why there isn't infinite current

 

[basboys80]

i think the current will not be infinity becuz there is an internal resistance of the coil (rL) ...