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FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ]

FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ]. LECTURE #5a CAPACITORS AND INDUCTORS HASIMAH ALI Programme of Mechatronics, School of Mechatronics Engineering, UniMAP. Email: hashimah@unimap.edu.my. CONTENTS. Introduction Capacitors. Introduction.

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FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ]

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  1. FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ] LECTURE #5a CAPACITORS AND INDUCTORS HASIMAH ALI Programme of Mechatronics, School of Mechatronics Engineering, UniMAP. Email: hashimah@unimap.edu.my

  2. CONTENTS • Introduction • Capacitors Introduction • Two new important passive linear circuit elements: capacitors and inductors. • Capacitors and inductors do not dissipate energy but store energy. • Therefore capacitors and inductors are called storage elements.

  3. CAPACITORS • A capacitor is a passive elements designed to store energy in its electric field. • Capacitors are the most important common electrical component and extensively used in electronics, communication, computer, and power system. • Example, they are used in the tuning circuits of radio receivers and as dynamics memory elements in computer system. A capacitor consists of two conducting plates separated by an insulator (or dielectric).

  4. CAPACITORS • Practically, the plates may be aluminum foil ; dielectric may be air ceramic, paper and mica. • When a voltage source is connected to the capacitor, the source deposits a positive charge q, on one plate and a negative charge –q on the other.

  5. CAPACITORS • Therefore the capacitor is said to store the electric charge. q= amount of charge stored, v= applied voltage and C=capacitance of the capacitor • Unit of capacitance= farad, F Capacitance is the ratio of the change on one plate of a capacitor to the voltage difference between the two plates, measured in farads (F). 1 farad = 1 coulomb/ volt

  6. CAPACITORS • Capacitance, C of a capacitor depends on the physical dimensions of the capacitor. • Example: for parallel plate capacitor, the capacitance is given: C= capacitance, A= surface area of each plate d= distance between plate ε = permittivity of the dielectric material between plates

  7. CAPACITORS • Three factors determine the value of capacitance: • The surface area of the plate – the larger the area, the greater the capacitance. • The spacing between the plates – the smaller the spacing , the greater capacitance. • The permittivity of the material – the higher the permittivity, the greater the capacitance Typical range value for capacitor: picofarad (pF)  microfarad (µF)

  8. CAPACITORS • According to passive sign convention, current is considered to flow into the positive terminal of the capacitor when the capacitor is being charges, and out of the positive terminal when the capacitor is discharging. • Current-voltage relationship of the capacitor:

  9. CAPACITORS • Voltage-current relation of the capacitor or This equation shows that capacitor voltage depends on the past history of the capacitor current. Means that the voltage across the capacitor at time t0

  10. CAPACITORS • The instantaneous power delivered to the capacitor is: • The energy stored in the capacitor:

  11. CAPACITORS • Take note of the important properties of a capacitor: • From the voltage-current relation equation, note that when the voltage across a capacitor is not charging with time (i.e dc voltage), the current through the capacitor is zero. • A capacitor is an open circuit to dc. • 2. The voltage on the capacitor must be continuous. The capacitor resists an abrupt change in the voltage across it. • The voltage on a capacitor cannot change abruptly.

  12. CAPACITORS • The ideal capacitor does not dissipate energy. It takes power from the circuit when storing energy in its field and returns previously stored energy when delivering power to the circuit. • A real, nonideal capacitor has a parallel-model leakage resistance, and can be neglected for most practical applications.

  13. CAPACITORS • Example: • Calculate the charge stored on a 3-pF capacitor with 20V across it. • Find the energy stored in the capacitor.

  14. CAPACITORS Solution:

  15. Further Reading • Fundamentals of Electric Circuits, 2nd Edition,McGrawhill Alexander, C. K. and Sadiku, M. N. O. • Electric Circuit, 8th Edition, Pearson, Nillson and Riedel. • Circuits,Brooks/ Cole, A. Bruce Carlson. • http://www.scribd.com/word/full/2031941?access_key=key-1vybbz6deqeinoosecmm

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