1. Monday(02/08): In class you will be completing a handout on

Capacitance since this topic also plays a major part in Ch.20. As you begin

reading Ch.20, pay careful attention to Electromotive Force, Current,

Ohm's Law, Resistance, and Resistivity. HW: Read and Study pages 578-84,

then solve problems 4, 6, 9, 14, and 18 on pages 612-13.

2. Tuesday(02/09): We may not have class due to FCAT Writes. Continue

your reading of Ch.20 and try to develop an understanding of Electromotive

Force, Current, Ohm's Law, Resistance, and Resistivity. HW: Again Read

and Study pages 578-84, then solve problems 4, 6, 9, 14, and 18 on pages

612-13.

3. Wednesday(02/10): Electric Power, Series and Parallel Wiring, and

Measuring Current and Voltage. HW: Read and Study pages 584-85,

pages 588-93, and pages 600-01, then solve problems 23, 26, 41, and 49

on pages 613-14.

4. Thursday(02/11): LAB on Ohm's Law. HW: Process lab data and

write lab report, due Monday.

5. Friday(02/12): Circuits Wired Partially in Series and Parallel, and

Internal resistance. HW: Read and Study pages 593-96, then solve

problems 58, 59, 61, and 63 on pages 614-15.

6. Monday(02/15): No School - Presidents Day. HW: Finish homework

assignments.

7. Tuesday(02/16): Capacitors in Series and Parallel, Electrical Safety.

HW: Read and Study pages 601-03 and 605, then solve problems 86, 87,

88, and 89 on page 616.

8. Wednesday(02/17): Review for Ch.20. HW: Finish all assigned work.

9. Thursday(02/18): Review for Ch.20. HW: Complete Review Handout.

10. Friday(02/19):TEST on Ch.20. HW: Go to website and study notes

for Ch.21 - Magnetic Forces and Magnetic Fields.

Very Important: If you have any questions or miss a class, see me before

school (8:00 - 8:30 AM), during Lunch, 7th hour, or after school. Best to send

an email to rpersin@fau.edu.

1. In electricity two fundamental concepts are current and voltage. For

any electrical element the voltage (V) across the element is the potential

difference between its two ends, while the current, I, (with I=Δq/Δt)

through the element is the rate at which electrical charges are flowing.

2. For many devices (but not all) the voltage and the current are

proportional to each other, with the units for each being Volts and

Amperes, respectively.

3. The current in a conductor is related to the motion of charge carriers

through the equation I=nqv_dA, where n is the density of charge carriers,

and v_d, the drift velocity.

4. Current density, J, can be calculated three ways with J=I/A, J=nqv_d,

and J=σE. The quantity, σ, "sigma", is referred to as conductivity.

5. We can also calculate resistance, R = pL/A with p, "rho", being the

resistivity, ( p = 1/σ). Resistivity also has a temperature dependence

which is given by the equation, ρ=ρ_o[1 + α·(T -T_o)], with α being a

temperature coefficient.

6. Since resistivity and resistance are proportional, we have a similar

equation for temperature dependence, R=R_o[1 + α·(T -T_o)].

7. The equation, V = I·R is known as Ohm's Law, and devices which obey

Ohm's Law are known as linear or ohmic devices.

8. Familiar examples are resistors which are found in radios, TV sets,

computers, and other electronic systems; the filaments of light bulbs; and

the heating elements of electrical ovens.

9. There are however other devices which do not obey Ohm's Law,

semiconductor devices such as transistors and diodes, and fluorescent

light bulbs. These are known as nonlinear devices.

10. Ohm's Law can be used to solve simple circuits. A complete circuit is one

which is a closed loop. It contains at least one source of voltage

(thus providing an increase in potential energy) and at least one potential

drop, i.e. a place where potential energy decreases.

11. If a potential difference (voltage) is maintained across a resistor, the

power, can be calculated with P = V·I = I²·R = V²/R.

12. An increase of potential energy in a circuit causes a charge to move from

a lower to a higher potential (ie. voltage). Note the difference between

potential energy and potential.

13. Because of the electrostatic force, which tries to move a positive charge

from a higher to a lower potential, there must be another 'force' to move

charge from a lower potential to a higher inside the battery.

14. This so-called force is called the electromotive force, or emf. The SI unit

for the emf is a volt (and thus this is not really a force, despite its name).

We will use a script E, the symbol , to represent the emf.

15. A decrease of potential energy can occur by various means. For example,

heat lost in a circuit due to some electrical resistance could be one source of

energy drop.

16. For resistors in series, use simple addition: R_EQ = R₁ + R₂ + … + R_n .

For resistors in parallel, use reciprocals: 1/R_EQ = 1/R₁ + 1/R₂ + … + 1/R_n .

17. Remember that for capacitors installed in a circuit the relationships are

reversed, with the equivalent capacitance in series (same Q, diff. V) being

1/C_EQ = 1/C₁ + 1/C₂ + … + 1/C_n , and for parallel (same V, diff. Q),

C_EQ = C₁ + C₂ + … + C_n . Also C = Q/V = ε_oA/d.

18. And still, we need these steps to solve any problem in Physics:

(i) read the problem and identify the given variables

(ii) determine what you are asked to solve for

(iii) find the correct equation to use

(iv) use Algebra, Trigonometry, and/or Calculus to isolate the unknown

(v) substitute-in the given information and simplify.

THE AP PHYSICS B ARCHIVES Ch.1: Physics Intro. Ch.2: Linear Motion. Ch.3: 2-Dim Motion. Ch.4&5: Newton's Laws. Ch.6: Work/Energy. Ch.7: Momentum. Ch.8&9: Rotary Motion. Ch.10: SHM. Ch.11: Fluids. Ch.12&13: Temp.&Heat. Ch.14&15: Thermodynamics. Semester Review. Ch.16: Waves & Sound. Ch.17: Wave Interference. Ch.18: Electric Fields. Ch.19: Electric Potential.