Estimating capacitance of capacitor

Introduction

The objective of this experiment is to make our own capacitor and estimate the capacitance using various methods. Multi-meter is used to help measuring the capacitance.

In this experiment we will test different methods which will help to us find capacitance of the capacitor. After that we will chose three methods which are more accurate than other methods and that methods will be used to find capacitance of the capacitor which will be made by ourselves. Then different values of the capacitance of the capacitor will be test for reliable.

A capacitor have two-terminal network with a certain capacity and low ohmic conductance. It is a device that is used for storing charge and energy of the electric field. Normally, capacitor consists from two electrodes in the form of plates. These plates are separated by a dielectric, whose thickness is smaller than size of plates.

The main characteristic of the capacitor is its capacitance, which characterizes the ability of a capacitor to store electrical charge. In the notation of the capacitor appears the rated capacity, while the actual capacity may vary considerably depending on many factors.

More about capacitance: Capacitance is also used for micro scheme of computer, refrigerator, TV screen and etc. (Bauman’s State Technical University, 2006).

Permittivity is a value (constant) that is found between an electric displacement and electric field intensity. Permittivity - determines the electric field strength in a particular environment. Examples of permittivity of different material which usually using as dielectric inside the capacitor: Polystyrene-2.5 , Mica-6.8 , Polytetrafluoroethylene-2 Polyethylene terephthalate-3 . (Bauman’s State Technical University, 2006).

A multi-meter is a device that used to measure different electrical properties such as current, resistance and AC/DC voltage. A multi-meter combines all voltmeter, ammeters, and anohmmeter.

Theory

Capacitance of the capacitor could be found by using formula:

The formula written above helps us to find the capacitance for flat plate capacitor. However, it was later proved that this formula could also be used for rolled capacitor.

When two capacitors are placed in series, charge comes to each plate with the same magnitude. This means: ; . Hence that; .

When a capacitor is charged, V across the capacitor could be found by this formula: and this formula to find current: .

When a capacitor is discharged, V across the capacitor can be calculated using the formula: and the current can be calculated with the formula: .

Where:

Method

Apparatus:

Power supply, leads, ruler, calipers, clips, known capacitor, aluminium foil, paper, multi-meter and video camera.

Part A

Method 1

Figure 1:

Figure 1 shows how the circuit was assembled.

Information:

So using the information above, for two capacitors in series:

We could find the capacitance of the second capacitor:

Result of Method 1:

We found value of second capacitor where; . However, real capacitance of the second capacitor is , so this method could not able used to find the real capacitance of capacitor, because the value I got from calculating is very different than the real value of capacitor. The reason why this occurs will be explain more in the summary section of part A.