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Stream lines

Stream lines . front plate slightly charged induces opposite charge on back plate. Brushes pull off charges charges collected in leyden jar (capacitor). Wimshurst Machine. Electric Field. Definition . Electric field is the

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Stream lines

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  1. Stream lines

  2. front plate slightly chargedinduces opposite charge on back plate.Brushes pull off chargescharges collected in leyden jar (capacitor) Wimshurst Machine

  3. Electric Field

  4. Definition • Electric field is the strength & direction of the forces in space surrounding a positive test charge

  5. Electric field as coulomb’s law • F = q1 * (k q2 /d2) rewrite the force equation F = q1 * E q1 is the positive test charge E is the field created by charge(s) q2

  6. Top tips on electric fieldE=0 inside a metal (faraday) cageField lines go from + to – chargesCloser field lines are stronger

  7. A B - C + Electric Fields Electric Field between 2 unlike charges Note that the distance between electric field lines at C is shorter than that at B. Distance between electric field lines at B is shorter than at A. Electrostatics

  8. Electric Fields Electric Field between 2 charged plates positive negative Electrostatics

  9. + + + + + + + + - - - - - - - - Electric Fields Electric Field between 2 charged plates Electrostatics

  10. coulombs, joules, volts • Coulomb= unit of charge • Joule = unit of energy • Volt= unit of energy per charge

  11. coulomb • How many charges are in 1C? coulomb? • 1C is about 6 billion billion charges)(1/1.6 x 10-19 = 6.25 x 1018) • The man, the law Charles Coulomb~1750

  12. Joules of energy • Charges have a type of energy called electron potential energy (PEe or U) High energy: + is close to +: ++ or + is far from –: + -

  13. It takes work to move charges against (opposite) an electric field High energy work needed to move + charge (W = F*d) E F + low energy

  14. (a) When a positive charge moves in the direction of an electric field, the field does positive work and the potential energy decreases. Work = qo E d POSITIVE charge moving in an E field.

  15. Volts is an energy density • Voltage is also called potential • 1 volt = 1 joule / 1 coulomb • Example: 12 V battery: every coulomb of charge has 12 joules of energy

  16. Examples • Static balloon 9 V battery (1hr,1A) 1 joule of energy 9x104 joule energy 0.001 C of charge 1x104C of charge 1/.0001 = 1000 volts 9/1 = 9 Volts

  17. Another c,j,v example • Van de graaf static generator has.. 1,000,00 volts (high) 1 joule of energy (low) .00001 coulombs of charge 1,000,000 v = 1 j/ .00001c

  18. Uniform electric field 2 situations Point Charges Force: F=q*E Force= k q1*q2 / d2 Electric potential energy Electric potential energy PE= F*d = q*E*d PE = F*d = k q1*q2 / d Voltage (electric potential)Voltage (electric potential) V= PE/q1 = q*E*d /q = E*d V= PE/q1 = k q2 / d2 Voltage difference: Voltage difference: DVe = D PE/q1 = E* Dd DVe = D PE/q1 = k q2 / d2 - kq2/ d1

  19. It takes work to move + charge against static forces like it takes work to lift against gravity • PEfinal • +++++ • + • Peiniitial work = gain in PE = F*d work

  20. Electrostaticsgravitational Force: F= kq1 q2 / d2 F= Gm1m2/d2 Field E= F/q1 = kq2/d2 g = F/m1 = Gm1/d2 potential energy PE= F*d = kq1 q2 / d PE = F*d= Gm1m2/d (using field) =qE*d = mg*h Potential V= PE/q1 = kq2 / d U= PE/m1 = G m2 / d (Using field) = E*d = g*h

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