Parallel Plate Capicitor Lab Report 95 Essay

Parallel Plate Capicitor Lab Report 95% Essay, Research Paper

Parallel Plate Capacitor and Dielectrics

Different materials were placed in between the plates of a parallel plate capacitor and the change in capacitance for each of the materials was tested using a galvanometer. The results were studied to determine the dielectric constant for each of the dielectric materials and to determine the permittivity of air.

By its self, results show that the parallel plate capacitor.s capacitance is inversely proportional to the distance between the plates. This relationship was plotted on a graph. The slope of this graph determined the permittivity of air to be 2.04E-10 F/m

For each material the capacitance increased by a constant factor, under a constant voltage. This is known as the material.s dielectric constant. The relationship between Capacitance versus the change in thickness of a certain type of paper was inversely proportional. This relationship was graphed and using its slope, the dielectric constant for the paper was calculated to be . The dielectric constant was also calculated for both plastic and wood to be and respectively.

This experiment concludes that the capacitance increases when the materials are placed in between the plates of the parallel plate capacitor.

INTRODUCTION

M

ichael Faraday first conducted experimentation of Dielectrics . The SI unit the Farad, to denote 1 Coulomb per Volt (C/V), was named after this scientist. Through his experiments on capacitors, he found that by filling the inner plates of a capacitor with different kinds of materials, it increases the capacitance by a constant factor, the dielectric constant. Each material used in between the plates (including air) has a dielectric constant. Faraday also discovered that dielectrics effect the .break down. voltage, the maximum potential difference that can be applied between the capacitor plates before the dielectric breaks down and forms a conducting path. . This experiment tries to conduct an experiment similar to Faraday.s on the properties of dielectrics pertaining only to changes in capacitance.

THEORY

To calculate some of information needed from the results, the experiment involved the following theory. The Capacitance (C) of the parallel plate capacitor can be calculated given by the area of the plates, the separation (d) between the plates and the permittivity of the material (e) between the plates:

C = eA / d equation 1

The dielectric constant (k) can be calculated, given the permittivity constant of the dielectric (e) and the permittivity of a vacuum (e0).

k = e / e0 equation 2

The dielectric constant can also be found given the measured capacitance (C) of the dielectric material with the capacitance of a vacuum (C0), by combining equations 1 and 2:

k = C / C0 equation 3

The Capacitance (C) can be determined given the a charge in Coulombs, and Voltage from the power supply:

C = q / V equation 4

Apparatus

Figure 1 describes how the apparatus for the experiment was set up. This involved a voltmeter, to measure the voltage being provided by the power supply with a double-pole-double throw switch. The load in the circuit was a resistor with the resistance of 1 Mega Ohm. The amount of charge in coulombs was measured using a galvanometer. There were also two capacitors used, one of known capacitance of 0.00948mF to calculate the sensitivity of the galvanometer, and a parallel plate capacitor with a vernier scale used in experimenting with dielectrics.

EXPERIMENTAL METHOD, OBSERVATIONS & RESULTS

Determining Galvanometer Sensitivity

In order to convert the measured deflection from the galvanometer into coulombs, the sensitivity of the galvanometer needed to be determined. This is done using the capacitor of a known capacitance, it being 0.00948 mF. The power being supplied is around 83V. After allowing some time for the capacitor to charge, the throw switch turned off the power, causing the capacitor to discharge. When this happens, the amount of deflection shows on the galvanometer and is recorded. This is repeated about three times to get an average deflection of 4.9mm. Using equation 4, from the Capacitance and the known voltage, the amount of charge in coulombs is determined and is then divided by the amount of deflection recorded. The sensitivity of the galvanometer calculated is 0.16×10-5 C/m The capacitor then is replaced with the parallel plate capacitor and is ready to conduct the following experiments.

Determining permittivity of Air

By finding the slope on a graph of the Capacitance versus the change in the inverse linear distance between the parallel plates, and by determining the area of the plates, the permittivity of the material between the plates can be calculated using equation 1.

A standard metric ruler is used to measure the diameter of the plates. The radius is then plugged into the area of a circle formula A=2pr2. The radius of the plate is 12.5cm and the area of the plates calculated is 981.7cm2 or 9.81E-2m2

Knowing the sensitivity of the galvanometer, it is now possible to use it to measure charge. At a potential difference of 202 volts, the amount of deflection caused by the capacitor discharge read on the galvanometer is rec

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