Current and Simple Circuits

1. Current and SimpleCircuits 1. Current 2. Conductivity Model 3. Current and Current Density

2. Reading Question What quantity is represented by the symbol J ? 1. Resistivity 2. Conductivity 3. Current density 4. Complex impedance 5. Johnston’s constant

3. Reading Question What quantity is represented by the symbol J ? 1. Resistivity 2. Conductivity 3. Current density 4. Complex impedance 5. Johnston’s constant

4. Reading Question The electron drift speed in a typical current-carrying wire is 1. extremely slow (≈10–4 m/s). 2. moderate (≈ 1 m/s). 3. very fast (≈104 m/s). 4. Could be any of 1, 2, or 3. 5. No numerical values were provided.

5. Reading Question The electron drift speed in a typical current-carrying wire is 1. extremely slow (≈10–4 m/s). 2. moderate (≈ 1 m/s). 3. very fast (≈104 m/s). 4. Could be any of 1, 2, or 3. 5. No numerical values were provided.

6. Reading Question All other things being equal, current will be larger in a wire that has a larger value of 1. conductivity. 2. resistivity. 3. the coefficient of current. 4. net charge. 5. potential.

7. Reading Question All other things being equal, current will be larger in a wire that has a larger value of 1. conductivity. 2. resistivity. 3. the coefficient of current. 4. net charge. 5. potential.

8. Current and Simple Circuits Current How can you show that a current is a flow of charge?

9. Current and Simple Circuits Current How can you tell if a current is flowing in a wire.

10. Knight has • Instantaneous current • This current is also given by • What does n, e and A represent? Current and Simple Circuits Current • How do we define instantaneous current? Write the equation and then define current in words.

11. Current and Simple Circuits Model of Conduction • Explain drift velocity vd. The charge carriers collide with impurities and phonons as the travel through the material to produce a current. The average velocity in the current direction is the drift velocity. vd

12. Average time between here and here. Average distance between here and here. Current and Simple Circuits Model of Conduction • In your group discuss electrical conduction in metals. Discuss terms like drift velocity, collision time, and mean free path. • Write a definition here. Collision time is the time between collisions. Mean free path is the average distance between collisions

13. Current and Simple Circuits Resistivity • Table 28.2 in your text lists a number of materials with their resistivity and conductivity. What metallic conductor has the largest conductivity?

14. Current and Simple Circuits Current density

15. Current and Simple Circuits A Puzzle

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17. Student Workbook Can you think of another? I could not!

18. Student Workbook Can you think of another? I could not!

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23. Class Questions These four wires are made of the same metal. Rank in order, from largest to smallest, the electron currents ia to id. 1. id > ia > ib > ic 2. ib = id > ia = ic 3. ic > ia = ib > id 4. ib = ic > ia = id 5. ic > ib > ia > id

24. Class Questions These four wires are made of the same metal. Rank in order, from largest to smallest, the electron currents ia to id. 1. id > ia > ib > ic 2. ib = id > ia = ic 3. ic > ia = ib > id 4. ib = ic > ia = id 5. ic > ib > ia > id

25. Class Questions Rank in order, from largest to smallest, the current densities Ja to Jd in these four wires. 1. Jb = Jd > Ja > Jc 2. Jb > Ja > Jc > Jd 3. Jb > Ja = Jd > Jc 4. Jc > Jb > Ja > Jd 5. Jc > Jb > Ja = Jd

26. Class Questions Rank in order, from largest to smallest, the current densities Ja to Jd in these four wires. 1. Jb = Jd > Ja > Jc 2. Jb > Ja > Jc > Jd 3. Jb > Ja = Jd > Jc 4. Jc > Jb > Ja > Jd 5. Jc > Jb > Ja = Jd

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34. Current and Simple Circuits +

35. Current and Simple Circuits Battery Look at old PP lecture

36. Current and Simple Circuits Current flows from higher potential (+) to lower potential (-). Battery or emf Resistor I For a current to flow you have to have a complete circuit.

37. Current and Simple Circuits What about current flow when there are two paths? Current splits at the junction or node.

38. Current and Simple Circuits Here is our simple circuit again with just an emf and resistor. Now we would like to look at the voltage difference around the circuit.

39. Current and Simple Circuits Here is our simple circuit again with just an emf and resistor. Now we would like to look at the voltage difference around the circuit.

40. A semiconductor is a material that has conductive between a conductor and an insulator. The conductivity is very strongly temperature dependent. Si Doped with Al is P type Doped with P is N type Current and Simple Circuits Semiconductor Material

41. Current and Simple Circuits • Field Effect Transistor

42. Superconducting elements Current and Simple Circuits • Superconductor A superconductor is a material that has zero resistance below a critical temperature TC TC

43. Current and Simple Circuits • Superconductor Perfect Conductor Meissner Effect - 4800 F

44. Current and Simple Circuits A Biological example: Ionic current across a cell membrane.

45. Class Questions