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Announcements

Announcements. Homework for tomorrow… (Ch . 29, Probs. 26, 28, & 60) CQ4: a) - (10 V/m) ihat b) - (5.0 V/m) ihat , - (20 V/m) ihat 29.16: -20 V 29.17: a) 1.3 x 10 -11 F b) 1.3 x 10 -9 C 29.36: V(r) = V 0 + ( λ / 2 πε 0 )* ln (R/r) Office hours… MW 12:30-1:30 pm

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 29, Probs. 26, 28, & 60) CQ4: a) -(10 V/m) ihat b) -(5.0 V/m) ihat, -(20 V/m) ihat 29.16: -20 V 29.17: a) 1.3 x 10-11 F b) 1.3 x 10-9 C 29.36: V(r) = V0+ (λ/2πε0)*ln(R/r) • Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am • Tutorial Learning Center (TLC) hours: M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm TR 8-6 pm, F 8-2 pm

  2. Review… • Capacitors in parallel… • Capacitors in series…

  3. 29.6:The Energy Stored in a Capacitor How much energy is transferred from the battery to the capacitor?

  4. 29.6:The Energy Stored in a Capacitor How much energy is transferred from the battery to the capacitor? or

  5. The Energy in the Electric Field Q: If a capacitor is analogous to a stretched spring, where is the stored energy?

  6. The Energy in the Electric Field Q: If a capacitor is analogous to a stretched spring, where is the stored energy? • A: In the E-field! When the capacitor is discharged, the energy is released as the E-field collapses.

  7. Quiz Question 1 A capacitor charged to 1.5 V stores 2.0 mJ of energy. If the capacitor is charged to 3.0 V, it will store • 1.0 mJ. • 2.0 mJ. • 4.0 mJ. • 6.0 mJ. • 8.0 mJ.

  8. Quiz Question 2 Consider a simple parallel-plate capacitor whose plates are given equal and opposite charges and are separated by a distance d. Suppose the plates are pulled apart until they are separated by a distance D>d. The electrostatic energy stored in the capacitor is • greater than • the same as • smaller than before the plates were pulled apart.

  9. Chapter 30 Current & Resistance (The Electron Current)

  10. 30.1:The Electron Current Charge carriers.. • the charges that move in a conductor. • are electrons in metals. • the outer electrons become detached from their parent nuclei to form a sea of electrons that can move through the solid.

  11. The Electron Current Define electron current, ie.. • # of electrons/second that pass through the cross-section of the conductor. • The number Ne of electrons that pass through the cross-section during the time interval Δt is

  12. The Electron Current The electron current, ie, in terms of the drift velocity, vd, & the number density, ne, is…

  13. The Electron Current The electron current, ie, in terms of the drift velocity, vd, & the number density, ne, is…

  14. Quiz Question 3 The electron drift speed, vd, in a typical current-carrying wire is • Extremely slow (~ 10–4 m/s). • Moderate (~ 1 m/s). • Very fast (~ 104 m/s).

  15. Quiz Question 4 A wire carries a current. If both the wire diameter and the electron drift speed are doubled, the electron current increases by a factor of • 2. • 4. • 6. • 8. • Some other value.

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