Basic Electronics

605-107

Resonance Lab

Materials Required:

Oscilloscope

Function Generator

Resistors: 100, 1.2kand 4.7k and

1 M potentiometer

Inductors: 33mH, 100mH

Capacitors: 820 pF, 0.01F

Procedure: Section 1 Series Resonance

  1. Connect the circuit of figure 1.
  1. Calculate and record the resonant frequency (fr) in Table 1. Use the following formula:

Calculate and record the frequencies ±5 kHz above and below resonance. Record these values in Table 1.

  1. Experimentally determine the value of resonance by placing an O’scope probe across the resistor. Vary the frequency of the function generator until you have the largest voltage possible measured across the resistor. The frequency displayed on the function generator corresponds to fr.
  1. Increase the frequency in 2 kHz steps from 10 to 50 kHz. Measure the voltage across R at each frequency and record the results in Table 2. Be sure to keep the applied voltage constant at each step. (MeasureVA at each step to be sure there is no change.)
  1. Measure and record VR, VL, and VC at resonance, and at 5 kHz above and below resonance (use fr as determined in step 3). Record the results in Table 3

Section 2: Parallel Resonance

  1. Calculate and record in Table 4 the resonant frequency of the circuit of Figure 2. Use the following formula:
  1. Connect the circuit of figure 2. Experimentally find resonance by finding the frequency which produces the smallest voltage across RS1. Record this value in Table 4.
  1. Measure and record in Table 4 the voltage across RS1, RS2, L, and C. Calculate and record mainline and tank currents using measured values of voltage and resistance (RS1 and RS2)
  1. Determine ZT as follows and record the results in Table 4. Replace RS1 with a 1 M rheostat (use two adjacent leads on a 1 M potentiometer). Adjust the circuit close to the resonant frequency and adjust RS1 so that its voltage equals the voltage across the tank. Record the value.

Note: When the voltage across the rheostat equals the voltage across the tank, its ohmic value is equal to the tank impedance. This is due to the laws of series circuits where equal resistances or impedances divide the applied voltage equally.

  1. Connect the circuit if figure 2. Increase the frequency in 250 Hz steps from 3500 to 6500 Hz. Measure the voltage across RS1, and the LC tank. Record the results in Table 5.

Figure 1

Figure 2

Basic Electronics

605-107

ResonanceLab

Name: ______Score: ______

Table 1

Calculated Value / Measured
Value
fr
fr
–5kHz
fr +5kHz

Table 2

F

/ VR /

F

/ VR
10 kHz / 32 kHz
12 kHz / 34 kHz
14 kHz / 36 kHz
16 kHz / 38 kHz
18 kHz / 40 kHz
20 kHz / 42 kHz
22 kHz / 44 kHz
24 kHz / 46 kHz
26 kHz / 48 kHz
28 kHz / 50 kHz
30 kHz

Table 3

VR / VL / VC
fr –5kHz
fr
fr +5kHz

Table 4

Measurement / Measured Value / Calculated Value
fr / HZ / HZ
VRS1 / Vp-p
VRS2 / Vp-p
VL / Vp-p
VC / Vp-p
ITank=VRS2/RS2 / A
Iline=VRS1/RS1 / A
ZT / 

Table 5

F

/ VRS1 / VLC Tank
3500 Hz
3750 Hz
4000 Hz
4250 Hz
4500 Hz
4750 Hz
5000 Hz
5250 Hz
5500 Hz
5750 Hz
6000 Hz
6250 Hz
6500 Hz
6750 Hz
7000 Hz
7250 Hz
7500 Hz
7750 Hz
8000 Hz