2/4/08 February 3, 2009 Warm-up  Draw a circuit diagram that includes a 2-cell battery, 2 resistors in series with an additional resistor in parallel with one of them.  Use arrow(s) to indicate the direction of conventional charge flow.

2/4/08 Objectives  Describe origination of charge flow in a circuit.  Draw and interpret schematic diagrams.  Explain operation of a capacitor.  Discuss voltage and apply to series and parallel circuits.  Describe charge flow during transient and steady-state processes.

2/4/08 Today’s Plan  Go over sections 2 +3  Complete Section 4 – Color coding  Section 5  Homework: Week 1 assignments due Thursday. Test 1 on Friday.

2/4/08 Resistance  Measured in ohms ()  Color-coding of resistors  Material, size, and shape affect resistance  Which bulb has greater resistance? (2.5)

2/4/08 Resistance Analogy  Straws and coffee stirrers.  Series vs. parallel straws (2.7, 2.10, 2.11)

2/4/08

Capacitor  2 layers of conducting material separated by insulator  Capacitor plates  Terminals  Capacitance  Farad

2/4/08 Where does charge originate?  Activity 3.5: Set up circuit using ROUND BULBS and BLUE CAPACITOR  What happens to the compass during the charging of the capacitor? Discharging?  Draw schematic that shows flow.

2/4/08 Where does charge originate?  In a diagram accurately depict the flow of charge during the charging process.

2/4/08 Are batteries necessary?  Activity 3.7: Use the genecon to light 2 bulbs in a circuit.  Where does the charge originate with a genecon?

2/4/08 Sections to complete  All 4 except 4.2, 4.3, 4.7  5.1, 5.2, 5.3, 5.5, 5.6, 5.8, 5.10, 5.11, 5.12, 5.14

2/4/08 Rechargeable Batteries  Are they really rechargeable or are they re-energizable?

2/4/08 Energy conversion  In which case is more energy converted? Discharging a capacitor through long bulbs? Discharging a capacitor through round bulbs? What are the energy conversions?

2/4/08 Why does charging of a capacitor stop?  Charge blue capacitor thru 2 long bulbs with 3 cell battery. Use compass to monitor flow. Add another 3 cell battery. Monitor flow.  Discharge the capacitor through the bulbs.

2/4/08 Electric Pressure  Battery changes the concentration of charge within the circuit. Charge is compressed.  Voltage measured in volts (V)  Positive side of battery—high pressure.

2/4/08 Color-coding  Tool for interpreting electric pressure.  Red, orange, yellow, green, blue in descending pressure.  Rules on page 45.  Charging and discharging a capacitor.

2/4/08 Practice  Color code circuits 4.14a-4.14d on page 50.

2/4/08 Pressure changes in wires  Set-up circuit 5.1 with identical bulbs and 4 D-cells.  Record relative brightness and color-code the circuit.  How was this condition achieved?

2/4/08 Activity 5.2  Set up circuit 5.2 with blue capacitor. Follow instructions for hooking up wires.  Color code the circuit at the INSTANT of connection; mid-way through charging process; after charging complete.

2/4/08 Charge Flow Rate  What must the charge flow rate be during and after the charging process?  Evident through relative brightness since all bulbs are equal.

2/4/08 Activity 5.3  Remove the capacitor without disturbing the circuit.  Any changes to bulb brightness?  How does the circuit reach steady state without the capacitor?

2/4/08 Series Circuit  Equal flow rate through all resistors in series when at steady state.  At hook-up, flow rate is transient and based on electric pressures.  Very fast process normally.

2/4/08 Activity 5.5  Set up circuit 5.5 with round and long bulbs.  Equal flow rates through all bulbs as just shown.  Is the pressure difference across all bulbs equal? Color code and explain.

2/4/08 Current Flow in Unlike Resistors  Flow rate determined by pressure difference and bulb’s resistance. Must both be considered.

2/4/08 Series Voltage Division  Total pressure change across battery shared among resistors. Not equal across unequal resistors.  Pressure difference is greater across higher resistance.

2/4/08 Parallel Resistors  Parallel pair has less resistance than a single bulb.  Lower resistance lets same pressure differences drive more flow.  Circuit has lower resistance but equal pressure differences (total) as earlier circuit.