EXPERIMENT 3: CAPACITORS
A. INTRODUCTION
A capacitor is an electric circuit element used to store electrical energy (charge) temporarily between its two parallel conductor plates and is separated by a non-conductive region with virtue of electric field. The charge stored is supplied by connecting the plates to a source of electricity. One plate stores the positive charge while the other stores the negative charge.
The ability of a capacitor to store charge is called capacitance. The SI unit for capacitance is Farad (F). A capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device. The larger the surface area of the plates of the capacitor, and the narrower the gap between them, the greater the capacitance is.
B. THEORY
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THEORY
A capacitor consists of two conductor parallel plate, which are separated by an electrical insulator between them. A capacitor is charged when electrons from a power source, such as a battery or generator, flow to one of the two plates. Since the two plates are separated by an insulating layer, the electrons cannot pass through it. Consequently, they build up on the negative plate, becoming negatively charged, while the electrons on the other plate are attracted to the positive terminal of the battery, making that plate a positively charged.
The capacitance of the capacitor is the ratio of the quantity of charge separated to the potential difference applied; Capacitance also depends upon both the “geometry” and the nature of the material that is the insulator between the parallel plate conductors.
Figure 3.2: The Cross-section of a parallel–plate capacitor.
From Gauss Law, the electric field between the two charges plates is; where Q is the charge on each plate. A is the plate area, and the constant εo is the permittivity of free space: εo = 8.85 × 10-12