Pr 101. LCR Resonance Ciecuit.

LCR-Circuits

Object: To determine the impedance of LCR circuit.

Apparatus Used: resistance, inductor coil, capacitor, connecting wires, a.c. voltmeter, mili- ammeter, low voltage a.c. source.

Theory

 In a circuit containing a inductor (L) a capacitor (C) and resistor (R), the net opposition to the current i.e the impedance is given by:

Procedure:

 

1.     Initially connect all the components (L,C and R) in series with source of a.c .

2.     Frequency of a.c is set at a fixed value.

3.     Value of resistance and capacitance is changed using the knob provided. Here inductor is fixed in the apparatus.

4.     Reading of current (I), total voltage (V), voltage across resistor (V_R), voltage across inductor (V_L), and voltage across capacitor (V_C) is noted.

5.     Impedance is observed from the table using

                         

6.     Further more calculate the value of z with the help of R, X_L and X_C. This value should be equal or approximately equal to the value of z observed.

Observation:

1.     Least count of voltmeter=........... volts

2.     Least count of mili-ammeter=........... mA

3.     Table for value of voltage and current

S.No.	Current	R-Circuit		L-Circuit		C-Circuit		LCR-Circuit (Total)
	I (mA)	VR (volt)	R = VR/I	VL (volt)	XL =VL/I	VC (volt)	XC =VC/I	V (volt)	Z=V/I
1.
2.
3.
4.
5.
6.

Result:

1. R=................................. W

2. X_L=............................... W

3. X_C=............................... W

                    4.     Z _Obs=............................. W

                    5.     Z_calculated=….................... W

Percentage Error:

Precaution and Discussion:

1.     Connections should be tight.

2.     Variation in voltage should be in slow manner.

3.     Reading of voltage and current should be started with zero.

4.     The current in the circuit should remain constant while measuring the voltage across R, L and C.