BEXS100 - Basic Electricity. Unit 19 Capacitors. Unit Objectives. Upon completion of this unit, you will be able to:. List the three (3) factors that determine the capacitance of a capacitor Explain electrostatic charge Determine the difference between polarized and nonpolarized capacitors.
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BEXS100 - Basic Electricity
Unit 19
Capacitors
Upon completion of this unit, you will be able to:
Introduction
Capacitors are “devices that oppose a change of voltage”, at their base level are a simple electrical storage device yet the applications for these devices are varied and wide ranging. Capacitors can be used in timing circuits, as electronic filters, and for power factor correction among other uses. Capacitors are used in both AC and DC circuitry.
The Capacitance of a Capacitor
The area of the plates
The distance between the plates
The type of “dielectric” used
Charging a Capacitor
Electrons are removed from one plate and deposited on the opposite plate
Charging a Capacitor
Current flows until voltage across capacitor is the same as the source voltage
Charging a Capacitor
The capacitor remains charged after the source of voltage (battery) is removed from the circuit
Capacitor “Leakage”
Leakage is current flow through the dielectric
Proportional to the resistance of the dielectric and the charge across the plates
More common designations of capacitance:
RC Time Constants
Capacitors charge at an exponential rate (63.2%)
RC Time Constants
Capacitors discharge at an exponential rate (63.2%)
RC Time Constants
Accurately determining the RC time constant for a given capacitor in a circuit
How long will it take to charge a 50 mF capacitor in a circuit with a 100,000 ohm resistor?
Answer: 25 Seconds
The Two Basic Groups of Capacitors
Polarized
&
Non-Polarized