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Electrical Energy and Capacitance

Explore the fundamentals of capacitance, energy storage, and capacitor technology in this comprehensive guide. Learn about parallel-plate capacitors, dielectrics, and the relationship between charge and potential difference in capacitors. Discover how capacitors store energy and the calculations involved in determining capacitance. Dive into the significance of Michael Faraday's contributions to electromagnetism and how capacitors play a crucial role in modern electrical systems.

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Electrical Energy and Capacitance

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  1. Electrical Energy and Capacitance Capacitance

  2. Capacitors and Charge Storage • Capacitor – acts as a storehouse of charge and energy • Typically consists of two metal plates separated by a small distance • Called a parallel plate capacitor • When connected to a battery, charge is transferred from one plate to another until the potential difference of the capacitor is equal to the potential difference of the battery • The two plates will have equal and opposite charges

  3. Capacitors and Charge Storage

  4. Capacitors and Charge Storage • Capacitance – the ability of a conductor to store energy in the form of electrically separated charges • Ratio of charge to potential difference • Measured in farads (F) • Equivalent to a coulomb/volt (C/V) • Named in honor of Michael Faraday who contributed greatly to our knowledge of electromagnetism • Capacitors typically range from microfarads (10-6) to picofarads (10-12) in strength

  5. Capacitors and Charge Storage • Capacitance = (magnitude of charge) / (potential difference) • C=Q/ΔV • Capacitance for a parallel-plate capacitor in a vacuum • Capacitance = (permittivity of a vacuum) * (area of one of the plates) / (distance between the plates)

  6. Capacitors and Charge Storage • C=ε0 *A / d • ε (lowercase sigma) represents permittivity of a medium • The subscript 0 means that the medium is a vacuum • Permittivity has a value of 8.85*10-12C2/N*m2 • Capacitance decreases with increasing distance • Capacitance increases with increasing size of the capacitor • Earth is so massive it is a excellent capacitor • Used for grounding • Can take a lot of charge without changing electric potential

  7. Capacitors and Charge Storage • The material between the plates can change the capacitance • By inserting an insulating material called a dielectric (such as air, rubber, glass, or waxed paper) between the plates, the capacitance increases • Surface charges build up on the dielectric and reduce the charge on the plates • More charge can be stored • Charge is rapidly released when discharged by a capacitor • Discharged by connecting the plates with a conductor

  8. Capacitors and Charge Storage

  9. Energy and Capacitors • Electrical potential energy stored in a charged capacitor • Electric potential energy = ½ * (charge on one plate) * (final potential difference) • PEelectric = ½QΔV • The greater the charge on the plates, the more work and therefore energy that is needed to move charges between the plates • Other forms of the equation • PEelectric = ½CΔV2 • PEelectric = Q2 / 2C • Capacitors have a maximum energy and charge they can store • Exceeding this maximum causes electrical breakdowns

  10. Energy and Capacitors

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