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Announcements

Announcements. Homework for tomorrow… (Ch . 30, CQ 11, Probs. 18, 20, 38) 30.3: 2.1 x 10 24 30.6: a) 4.6 x 10 21 b) 4.4 x 10 -12 m 30.7: 1.0 x 10 19 s -1 Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am Tutorial Learning Center (TLC) hours:

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 30, CQ 11, Probs. 18, 20, 38) 30.3: 2.1 x 1024 30.6: a) 4.6 x 1021 b) 4.4 x 10-12 m 30.7: 1.0 x 1019 s-1 • 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. Chapter 30 Current & Resistance (Conductivity and Resistivity & Resistance and Ohm’s Law)

  3. Review… • Current.. • Current Density.. • Kirchoff’s Junction Rule.. • Current Density related to the E-field..

  4. Quiz Question 1 The current density in this wire is • 4  106 A/m2. • 2  106 A/m2. • 4  103 A/m2. • 2  103 A/m2. • Some other value.

  5. 30.4:Conductivity and Resistivity How the current density, J, is related to the E-field driving the current: where SI Units?

  6. 30.4:Conductivity and Resistivity How the current density, J, is related to the E-field driving the current: Where SI Units?

  7. Quiz Question 2 Both segments of the wire are made of the same metal. Current I1 flows into segment 1 from the left. How does current I1 in segment 1 compare to current I2 in segment 2? • I1> I2. • I1 = I2. • I1 < I2. • There’s not enough information to compare them.

  8. Quiz Question 3 Both segments of the wire are made of the same metal. Current I1 flows into segment 1 from the left. How does current density J1 in segment 1 compare to current density J2 in segment 2? • J1J2. • J1J2. • J1J2. • There’s not enough information to compare them.

  9. Quiz Question 4 Both segments of the wire are made of the same metal. Current I1 flows into segment 1 from the left. How does the electric field E1 in segment 1 compare to the electric field E2 in segment 2? • E1 > E2. • E1 = E2 but not zero. • E1 < E2. • Both are zero because metal is a conductor. • There’s not enough information to compare them.

  10. 30.4:Conductivity and Resistivity Define the resistivity… SI Units?

  11. 30.4:Conductivity and Resistivity Define the resistivity… SI Units?

  12. 30.4:Conductivity and Resistivity Define the resistivity… SI Units?

  13. i.e. 30.6:The E-field in a wire A 2.0 mm diameter aluminum wire carries a current of 800 mA. What is the E-field strength inside the wire?

  14. 30.5:Resistance and Ohm’s Law How is the current, I, related to the potential difference, ΔV in a wire?

  15. 30.5:Resistance and Ohm’s Law How is the current, I, related to the potential difference, ΔV in a wire? SI Units of R? - Ohm’s Law

  16. 30.5:Resistance and Ohm’s Law How is the current, I, related to the potential difference, ΔV in a wire? SI Units of R? - Ohm’s Law

  17. 30.5:Resistance and Ohm’s Law Notice: • Resistivity, ρ, describes just the material. • Resistance, R, characterizes a specific piece of the conductor with a specific geometry. Resistance of a wire

  18. Quiz Question 5 Wire 2 has twice the length and twice the diameter of wire 1. What is the ratio R2/R1 of their resistances? • 1/4. • 1/2. • 1. • 2. • 4.

  19. Resistance and Ohm’s Law • A battery is a source of potential difference Vbat. • The battery creates a potential difference Vwire= Vbatbetween the ends of the wire. • The potential difference in the wire Vwire generates an E-field in the wire. • The E-field establishes a current I = JA = σAE in the wire. • The current in the wire is determined jointly by the battery and the wire’s resistance, R to be: • IVwire/R

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