1. Reading Quiz
2. The electron drift speed in a typical current-carrying wire is
extremely slow (≈10–4 m/s).
moderate (≈ 1 m/s).
very fast (≈104 m/s).
Could be any of A, B, or C.
No numerical values were provided.
What quantity is represented by the symbol J ?
Resistivity
Conductivity
Current density
Complex impedance
Johnston’s constant
Answer: C

2. Reading Quiz
3. All other things being equal, current will be larger in a wire that has a larger value of
conductivity.
resistivity.
the coefficient of current.
net charge.
potential.
4. The equation I = ∆V/R is called
Ampere’s law
Ohm’s Law
Faraday’s Law
Weber’s Law
Answer: E

3. What quantity is represented by the symbol J ?
Resistivity
Conductivity
Current density
Complex impedance
Johnston’s constant

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

5. All other things being equal, current will be larger in a wire that has a larger value of
conductivity.
resistivity.
the coefficient of current.
net charge.
potential.

6. The equation I = ∆V/R is called
Ampère’s law.
Ohm’s law.
Faraday’s law.
Weber’s law.
Answer: C

7. Exam Grading 10 point total
Grade for the “Initial Effort”:
Satisfactory initial effort : 4pt
Missing explanations or steps:3pt
Major problem parts missing (or didn’t finish): 2pt
Very little coherent effort:1pt
No initial effort: 0pt 
Note:
it is a grade per problem.
This grade has nothing to do with whether that effort is correct: students can earn a full 4 points on this part and be completely wrong.
No comments are made on the problem.

8. Exam Grading – con’t
Post the printed solutions on BB or on the website
Students then use the printed solutions to correct their work using a different color ink.
Re-collect the work and grade for
Correction Quality
Correction Needed

9. Exam Grading Correction Quality: Solution is now completely correct 3
Solution is now completely correct 3
Minor issues were not corrected 2
Major issues were not corrected 1
No correction effort 0
and for Correction needed:
No correction was necessary 3
Minor corrections were needed 2
Important corrections were needed 1
Initial effort needed a complete rewrite 0

12. The Electron Current
Pushing on the sea of electrons with an electric field    causes the entire sea of electrons to move in one direction    like a gas or liquid flowing through a pipe.
This net motion, which takes place at the drift speed vd,    is superimposed on top of the random thermal motions of    the individual electrons.
The electron current is the number of electrons per    second that pass through a cross section of a wire or other    conductor. ne is the number density of electrons.
The electron current in a wire of cross-sectional area A is

13. Current
If Q is the total amount of charge that has moved past a point in a wire, we define the current I in the wire to be the rate of charge flow:
The SI unit for current is the coulomb per second, which is called the ampere. 1 ampere = 1 A = 1 C/s.
The conventional current I and the electron current ie are related by

15. The Current Density in a Wire
The current density J in a wire is the current per square meter of cross section:
The current density has units of Amps/m2.

16. Kirchhoff’s Junction Law
For a junction, the law of conservation of current requires that
where the Σ symbol means summation.
This basic conservation statement – that the sum of the currents into a junction equals the sum of the currents leaving – is called Kirchhoff’s junction law.

18. Conductivity and Resistivity
The conductivity of a material is
Conductivity, like density, characterizes a material as a whole.
The current density J is related to the electric field E by:
The resistivity tells us how reluctantly the electrons move in response to an electric field:

21. Resistance and Ohm’s Law
The resistance of a long, thin conductor of length L and cross=sectional area A is
The SI unit of resistance is the ohm. 1 ohm = 1 Ω = 1 V/A.
The current through a conductor is determined by the potential difference ΔV along its length:

22. Ohm’s Law
Ohm’s law is limited to those materials whose resistance    R remains constant—or very nearly so—during use.
The materials to which Ohm’s law applies are ohmic.
The current through an ohmic material is directly    proportional to the potential difference.
Metal and other conductors are ohmic devices.

23. Demo, Activity, and Workbook
Van de Graff Generator
Capacitor Activity
Workbook p – 31.10