4r=6 (30) The bigger is,the smaller Af will be.Thus the resonant peak will be sharper.Therefore the frequency selectivity will be better is a bigger Q is chosen. 【Equipment】 Digital multimeter,digital capacitance table,power function signal generator,digital storage oscilloscope,transistors millivoltmeter experiment wiring boards,resistance,capacitance, inductance,flash generator;and photo sensor and so on. 【Experiment】 1.Observe alternative current waves produced by a signal generator.The signals include a sinusoidal wave,square wave,triangular waves,impulse wave and TTL (transistor-transistor logic)wave.Roughly draw the waves.Record the peak-to peak value,period or frequency. 2.Connect the phase-shifting circuit as shown in Fig.1.Use the "cursor"of the oscillator to measure the phase difference between the voltage of the input signal and the capacitor,Find 3 frequencies which make the differences close to 0 degree,at 45 degree and close to 90 degree,respectively.Draw the vector diagram as is illustrated by Fig.3. 3.(Optional)Connect the circuit as in Fig.4.Double-check the circuit and then connect the power.When the indicator of the flash generator is on,push the trigger button.After that there should be a flash generated,then,adjust the trigger mode of the oscilloscope so that it is in the single triggered mode.Properly adjust the trigger voltage and the channel sensitivity, and two sampled waves will be on the screen as in Fig.5.To properly measure the residual voltage,disconnect the power switch K,and try not to touch the electrodes of the capacitor when changing the energy storing capacitor.When removing the capacitors,make sure that the capacitors are discharged.In order to make the silicon photoelectric diode D to always be biased inversely,the position of D and the flashing lamp should be adjusted so that the lowest voltage on D is about 3V. 4.Choose various RC or RL to build up series circuits.Measure and describe the wave pattern of capacity or inductance when time constant is larger or smaller than the cycle of the square wave.Calculate the time constant and compare it with the theoretical value. 5.Choose various RLC to build up series circuits.Measure and describe the capacitor voltage during underdamping,critical damping and overdamping process.Calculate the time constant and compare it to the theoretical value.Notice that the cycle of square wave should be much longer than the time constant. 6.Input simple sinusoidal alternating voltage U;to the RC and RL series circuit.Plot the amplitude-frequency and phase frequency curve under the same time axis.The amplitude should be represented in relative change. 7.Input simple sinusoidal alternating voltage U;to the series RLC circuit.Measure the component voltage or various components changing with the frequency of Ui.Plot the amplitude-frequency and phase frequency curve.The requirement is the same to item 6. Determine the resonant frequency,calculate the quality factor,choose 20 different frequencies respectively.Take another capacitor to make a comparison.9 Q f f 0 Δ = （30） The bigger Q is, the smaller Δf will be. Thus the resonant peak will be sharper. Therefore the frequency selectivity will be better is a bigger Q is chosen. 【Equipment】 Digital multimeter, digital capacitance table, power function signal generator, digital storage oscilloscope, transistors millivoltmeter experiment wiring boards, resistance, capacitance, inductance, flash generator; and photo sensor and so on. 【Experiment】 1. Observe alternative current waves produced by a signal generator. The signals include a sinusoidal wave, square wave, triangular waves, impulse wave and TTL (transistor-transistor logic) wave. Roughly draw the waves. Record the peak-to peak value, period or frequency. 2. Connect the phase-shifting circuit as shown in Fig.1. Use the “cursor” of the oscillator to measure the phase difference between the voltage of the input signal and the capacitor, Find 3 frequencies which make the differences close to 0 degree, at 45 degree and close to 90 degree, respectively. Draw the vector diagram as is illustrated by Fig. 3. 3. (Optional) Connect the circuit as in Fig.4. Double-check the circuit and then connect the power. When the indicator of the flash generator is on, push the trigger button. After that there should be a flash generated, then, adjust the trigger mode of the oscilloscope so that it is in the single triggered mode. Properly adjust the trigger voltage and the channel sensitivity, and two sampled waves will be on the screen as in Fig. 5 . To properly measure the residual voltage, disconnect the power switch K, and try not to touch the electrodes of the capacitor when changing the energy storing capacitor. When removing the capacitors, make sure that the capacitors are discharged. In order to make the silicon photoelectric diode D to always be biased inversely, the position of D and the flashing lamp should be adjusted so that the lowest voltage on D is about 3V. 4. Choose various RC or RL to build up series circuits. Measure and describe the wave pattern of capacity or inductance when time constant is larger or smaller than the cycle of the square wave. Calculate the time constant and compare it with the theoretical value. 5. Choose various RLC to build up series circuits. Measure and describe the capacitor voltage during underdamping, critical damping and overdamping process．Calculate the time constant and compare it to the theoretical value. Notice that the cycle of square wave should be much longer than the time constant. 6. Input simple sinusoidal alternating voltage Ui to the RC and RL series circuit. Plot the amplitude-frequency and phase frequency curve under the same time axis. The amplitude should be represented in relative change. 7. Input simple sinusoidal alternating voltage Ui to the series RLC circuit. Measure the component voltage or various components changing with the frequency of Ui. Plot the amplitude-frequency and phase frequency curve. The requirement is the same to item 6. Determine the resonant frequency, calculate the quality factor, choose 20 different frequencies respectively. Take another capacitor to make a comparison