# The capacitance of two unknown capacitors through the use of a circuit and oscilloscope

A variety of capacitors shown in color in circuit board. Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. Both plates hold equal charges, and as the positive plate collects a charge, an equal charge flows off the negative plate.

Depending on its size, the capacitor may need a second or two to collect enough energy for another flash. In this example, it is assumed that: Therefore, when trying to decipher the value of an unknown capacitor with an oscilloscope, use a known voltage for Vin, and a known resistor R.

This time is called the time constant of the Resistor-Capacitor combination. Repeat the above procedure using at least 5 other values of C2.

Follow the same procedure as with C1. Is the resulting circuit consisting of the battery and the capacitor C1 a series circuit? Is it a series circuit or a parallel circuit? The dielectric is the best possible insulator for the application.

When the DPDT switch is thrown to position 2the series combination is connected to a potential difference V0 and the oscilloscope measures the voltage across C1. The capacitance value of a capacitor is measured in farads Funits named for English physicist Michael Faraday — Some digital multimeters offer a capacitance measurement function so technicians can: At any time t seconds after the capacitor starts charging, the voltage Vc on the capacitor changes as: Capacitors come in various shapes.

We will also study the behavior of capacitors connected in series. If the voltage Vc is seen on the oscilloscope, the same graph will be seen there as well. Capacitance is expressed as the ratio of the electric charge on each conductor to the potential difference i. Here, Vc is the voltage on the capacitor C, at time t, Vin is the final voltage the capacitor will be charged to, and R is the resistance through which the capacitor is charging.

Now, determine the value of Repeat the measurement a few times to get a good estimate of its uncertainty.

Mazur, American Technical Publishers. Rule of thumb for using oscilloscopes: While batteries release energy gradually, capacitors discharge it quickly. The oscilloscope will show both the charging as well as the discharging waveforms. In the same process, a smaller capacitor charges in a shorter time than a capacitor that is larger in value.

Once again, it may be the same model as the one you will use or it may be a slightly different model that looks nearly the same. Digital Multimeter Principles by Glen A.Objective: Through use of the oscilloscope and function generator, the aim of this lab is to measure capacitance of two different capacitors.

This will be done by measuring the time constant of each, as well as a graphical method. The behavior of capacitors in series and parallel will also be observed and measured. Experiments with a capacitor Introduction. A storage oscilloscope enables the voltage/time graph for a capacitor charging through a resistor to be displayed and, from the print-out, a value of the time constant for the circuit to be calculated.

A capacitor of unknown value (approximately 1 µF for the values used here). A battery (a 9 V PP3. Oscilloscope Measurement Lab Measuring Impedance and Capacitance with an Oscilloscope and Function Generator.

A circuit made up of a resistor and capacitor causes a phase shift between the current and voltage. In this lab, Repeat steps 3 through 6 for the unknown capacitor. Figure 2. Another way to measure the capacitance is to include the unknown capacitor in a resonance circuit. The accuracy is directly dependent on the used reference inductor.

Inductors with a small tolerance are rare and expensive. Measurement arrangement Fig. Resonance method measuring arrangement for capacitors. 1. Replace the known capacitor with the unknown capacitor in the circuit.

2.

Set the resistance to about 4k, and make the necessary adjustments to the oscillo-scope settings to again obtain the appropriate display on the oscilloscope.

3. Measure and record R, f, V, the oscilloscope settings, and T 1=2. 4. Tau is the time required to charge a capacitor that is in series with a resistor to a level of % of the initial value, typically 0 V. A digital storage oscilloscope can readily display voltage plotted against time in a capacitor charging or discharging through a resistor.

The capacitance of two unknown capacitors through the use of a circuit and oscilloscope
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