ECEN 102 (Capacitors)

• Capacitance is the ability of a dielectric to hold or store an electric charge.
• The more charge stored for a given voltage, the higher the capacitance.
• The symbol for capacitance is C, and the unit is the farad (F), named after Michael Faraday.
• A capacitor consists of an insulator (also called a dielectric) between two conductors.
• The conductors make it possible to apply voltage across the insulator.
• The most important property of a capacitor is its ability to block a steady DC voltage while passing AC signals.
• . The higher the frequency, the less the opposition to AC voltage.
• Capacitors are a common source of troubles because they can have either an open at the conductors or a short circuit through the dielectric.
• Electrons from the voltage source accumulate on the side of the capacitor connected to the negative terminal of V.
• The opposite side of the capacitor connected to the positive terminal of V loses electrons.
• The excess of electrons produces a negative charge on one side of the capacitor, and the opposite side has a positive charge.
• The charge on only one plate need be considered because the number of electrons accumulated on one plate is exactly the same as the number taken from the opposite plate.
• Charging - the voltage source is simply redistributing some electrons from one side of the capacitor to the other.
• Charging continues until the potential difference across the capacitor is equal to the applied voltage.
• Without any series resistance, the charging is instantaneous.
• Storage means that the charge remains even after the voltage source is disconnected.
• The measure of how much charge can be stored is the capacitance C.
• More charge stored for a given amount of applied voltage means more capacitance.
• Components made to provide a specified amount of capacitance are called capacitors, or by their old name condensers.
• A capacitor consists simply of two conductors separated by an insulator.
• Capacitance is the ability to store charge.
• Any voltage has a field of electric lines of force between the opposite electric charges.
• Electric field - the magnetic lines of force of the magnetic field associated with electric current.
• What a capacitor does is concentrate the electric field in the dielectric between the plates.
• The electric fi eld is concentrated in the capacitor, instead of being spread out in all directions.
• The capacitor has opposite charges because of electrostatic induction by the electric field.
• In a capacitor, is the electric charge stored in the dielectric or on the metal plates? Dielectric
• What is the unit of capacitance? Farad
• Applied voltage puts charge in the capacitor.
• The accumulation of charge results in a buildup of potential difference across the capacitor plates.
• When the capacitor voltage equals the applied voltage, there is no more charging.
• The charge remains in the capacitor, with or without the applied voltage connected.
• The capacitor discharges when a conducting path is provided across the plates, without any applied voltage.
• It is necessary only that the capacitor voltage be more than the applied voltage. Then the capacitor can serve as a voltage source, temporarily, to produce discharge current in the discharge path.
• The capacitor discharge continues until the capacitor voltage drops to zero or is equal to the applied voltage.
• The negative battery terminal repels free electrons on one side of the conductor plate.
• The positive battery terminal attracts free electrons on one side of the conductor plate.
• The charging process continues until the capacitor voltage equals the battery voltage.
• The effect of electric lines of force through the dielectric results in storage of the charge.
• The electric fi eld distorts the molecular structure so that the dielectric is no longer neutral.