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— PHYS 375: Lab 3 – AC signal and capacitors –PurposesGet familiar with the usage of an oscilloscope and a function generator. Understand how adigital multimeter works with AC signal. Show that the current flowing in a capacitor isproportional to the time derivative of the voltage across the capacitor.1 Measuring AC signalBuild the circuit shown in Figure 1. Setup the oscilloscope to measure the output voltage of thecircuit Vf. Take R = 33 kΩ. The alternating current (AC) voltage is provided by a functiongenerator (set to sinusoidal mode). Set the output voltage V of the function generator such thatat f ' 100 Hz, the voltage Vfpeak value reads 5 V approximately on the oscilloscope.RVVfFigure 1: Circuits part 1.• Measure the peak value on the oscilloscopeˆVf.• Measure the peak-to-peak value using the oscilloscope VP Pf• Insert a digital multimeter in parallel to the oscilloscope and measure the Vdmmfusing themultimeter?• Compute the ratioˆVf/Vdmmf. Does this ratio agree with what derived in the handout?• What is the cut-off frequency of this filter. Describe in what sense this circuit acts as ahigh pass filter.• Redo the above set of measurement for the cases of a square and rectangular signals.• For these two types of signal try to vary the duty cycle of the function generator andinterpret the change in Vdmmf12 Derivative of a signalBuild the circuit shown in Figure 2. Setup the oscilloscope to measure the output voltage of thecircuit Vf. Take C = 0.001 µF. The alternating current (AC) voltage is provided by a functiongenerator (set to sinusoidal mode). Set the output voltage V of the function generator such thatat f ' 100 Hz, the voltage Vfreads 5 V approximately.VVfCFigure 2: Circuits part 2.1. Setup a digital multi meter to measure the current flowing in the circuit2. For various frequency, measure the current flowing through the circuit and the voltageacross the capacitor. The Oscilloscope will give you a peak value while the digital multi-meter will provide an rms value of the current3. Compute the impedance modulus |Z| of the system (remember to convert all quantities tothe same type of either peak or rms).4. Plot |Z| versus the frequency f. Does the curve match the expected dependency of theimpedance versus f.5. Replace the digital multimeter by small resistor (R = 500 Ω) and monitor the voltageacross the resistor on the second channel of the oscilloscope. Set the frequency to 100 Hz,and sketch the signals you observe on the oscilloscope.6. Repeat step 5 for a square and triangular signal. Is one of the signal the time derivativeof the


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NIU PHYS 375 - AC signal and capacitors

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