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Electrical Energy and Capacitance

Electrical Energy and Capacitance. Capacitance. 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

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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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