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Electrical Energy and Capacitance Physics - Chapter 18

Electrical Energy and Capacitance Physics - Chapter 18. Ch. 18-1 (Pages 666-669) I. Electrical Energy & Electric Force. Electrical potential energy - PE associated with an object due to position relative to an electric force. Results from interactions of 2 objects’ charges.

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Electrical Energy and Capacitance Physics - Chapter 18

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  1. Electrical Energy and Capacitance Physics - Chapter 18

  2. Ch. 18-1 (Pages 666-669) I. Electrical Energy & Electric Force • Electrical potential energy - PE associated with an object due to position relative to an electric force. • Results from interactions of 2 objects’ charges

  3. ΔPE electric change in electric potential energy (final minus initial) • Factors determining PE electric 1. Charge 2. Strength of electric field 3. Position in the direction of the field

  4. PE electric = -q E d d = displacement from ref. point q = charge E = electric field strength

  5. PE electric= Kc (q1q2) r r = distance between charges in meters Kc=8.99 x 109 N(m2/C2) (pairs of charges) Reference point assumed to be infinity Homework : Page 669 #1-4

  6. 18-2 Potential difference (p.670-675) • Electric potential - electric potential energy of a charged particle in an electric field (divided by its charge) • Electric potential (V) = electric potential energy charge of the particle V = PE electric q

  7. V is measured in volts 1 volt = 1 J/C • Potential difference- change in electrical potential energy (V) *only changes in electric potential are significant and important • ΔV = PE electric q • ΔV Measured in volts (V) = 1 J/coulomb

  8. ΔV measures the change in energy per unit of charge • A potential difference within a battery causes charge to move • ex.  12 Volt car battery -positive terminal has electric potential of 12 V -negative terminal has electric potential of 0 V • positive terminal has a higher electric potential then the negative terminal

  9. As 1 coulomb of charge moves from negative to the positive terminal the battery does work on the charge to increase the PE electric of the charge to 12 J of electric potential energy • Each coulomb of charge that leaves the battery would have 12 J of energy • This energy is given up to the parts of the device which is run from the battery

  10. 18-3 Capacitance • Capacitor - a device used in electrical circuits to store charge • A storehouse of charge • Stores positive and negative charges separately

  11. Parallel-plate-capacitor-two metal plates separated by a small distance • Connected to the 2 terminals of a battery (once charged, battery removed) • Charge is removed from one plate and accumulates on another

  12. Capacitance- the ability of a conductor to store energy in the form of electrically separated charges •  Ratio of net charge on each plate to potential difference

  13. SI unit is the farad (F) = coulomb/volt • Capacitance depends on the size, shape, and materials of the capacitor • Larger plates = more storage of energy • Materials between plates can change capacitance

  14. Charged capacitors release energy rapidly •  Ex. – camera flash, computer keyboard

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