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Introduction to Capacitors and Capacitance Online Resource for ETCH 213 Faculty: B. Allen Capacitor A device that stores electrical energy in the form of an electric field that exists within a dielectric (insulator) between two conducting plates, each of which is connected to a load. This device was originally called a condenser. Online Resource for ETCH 213 Faculty: B. Allen Charging a capacitor Online Resource for ETCH 213 Faculty: B. Allen Electrostatic or electric field A force field produced by static electric charges. Also called a voltage field, it is a field or force that exists in space between two different potentials or voltages. Current generates a magnetic field. Voltage generates an electric field. Online Resource for ETCH 213 Faculty: B. Allen Field strength The strength of a electromagnetic field at a given point. Online Resource for ETCH 213 Faculty: B. Allen Field strength (V/m) = Charge difference (V) volts Distance between plates (d) meters Online Resource for ETCH 213 Faculty: B. Allen Electric polarization Electric Polarization – A displacement of bound charges in a dielectric when placed in an electric field. Dielectric – Insulating material between two (di) plates in which the electric field exists. Online Resource for ETCH 213 Faculty: B. Allen Unit of Capacitance Farad (F) – A one farad capacitor stores 6.24 × 1018 electrons or A 1 F capacitor stores 6.24 × 1012 electrons Online Resource for ETCH 213 Faculty: B. Allen Capacitance, C (farads) = Charge, Q (coulombs) Voltage, V (volts) Q =C × V Online Resource for ETCH 213 Faculty: B. Allen Factors determining capacitance Area of the plates (A) Distance between the plates (d) Dielectric constant (K) C= 8.85 × 10-12 × K × A d Online Resource for ETCH 213 Faculty: B. Allen Dielectric breakdown and leakage Breakdown Voltage – The voltage at which breakdown occurs in a dielectric or insulator. Leakage Current – Small, undesirable flow of current through an insulator or dielectric. Online Resource for ETCH 213 Faculty: B. Allen Capacitors in parallel CT = C1 + C2 + C3 +… Online Resource for ETCH 213 Faculty: B. Allen Capacitors in series 1 = 1 CΤ C1 + 1 C2 + 1 + C3 1 + ….. C4 Online Resource for ETCH 213 Faculty: B. Allen Voltage across a capacitor in series VX = CT CX VT Online Resource for ETCH 213 Faculty: B. Allen Types of capacitors Fixed-Value Capacitor – A capacitor whose value is fixed and cannot be varied. Mica Capacitor – A fixed capacitor that uses mica as the dielectric between its plates. Ceramic Capacitor – A capacitor in which the dielectric material used between the plates is ceramic. Online Resource for ETCH 213 Faculty: B. Allen Coding of capacitors Alphanumeric labels Online Resource for ETCH 213 Faculty: B. Allen Color coding of capacitors Online Resource for ETCH 213 Faculty: B. Allen Capacitor time constant DC charging Online Resource for ETCH 213 Faculty: B. Allen Time constant τ = R × C The time constant is the time needed for either a voltage or current to rise to 63.2% of the maximum or a fall to 36.8% of the initial value. The time constant of an RC circuit is equal to the product of R and C. Online Resource for ETCH 213 Faculty: B. Allen Capacitor charging Online Resource for ETCH 213 Faculty: B. Allen Online Resource for ETCH 213 Faculty: B. Allen AC charge and discharge. (a) Capacitor will block DC. (b) Capacitor will pass AC. Online Resource for ETCH 213 Faculty: B. Allen Phase relationship between capacitor current and voltage Online Resource for ETCH 213 Faculty: B. Allen End of Introduction to Capacitors and Capacitance Online Resource for ETCH 213 Faculty: B. Allen