1. What we will do What we will learn 13Px 14 Mahuru 2017
Preliminaries and roll
How to kick off well
Revisit a capacitor and why it will not let DC through
Why a capacitor stops DC
Watch a capacitor let AC through and figure out why
Why a capacitor permits AC
Introduce a new concept: reactance
What it is PLUS how it is both similar to and different from resistance
Examine the two things that capacitive reactance is affected by
How to put together a new formula
Set some questions on capacitive reactance for HW
How to apply new knowledge and complete the HW before 20 Nov

2. HW item Skills practiced Elex: Pages 184 - 185
Due Tuesday, the 22nd of Aug 2017
Revision of NCEA2 magnetism and also intro to idea of flux
Elex: Pages
Faraday’s Law
Elex: Pages
Lenz’s Law
Elex: Pages
Due Tuesday, the 5th of Sept 2017
Transformers
Elex: Pages 196
Self-Inductance, the inductor and back EMF
Elex: Pages
Due Friday, the 15th of Sept 2017
Transient currents and voltages in LR DC circuits
Elex: Pages
Inductors in DC circuits
Elex: Pages
Due Thursday, the 21st of Sept 2017
A.C. and R.M.S.

3. Homework Marking No. of marks What for 1
Having sketches & FULL working for all
Neat presentation and down-page format
Answer underlined and units given
Self marked and all correct – eventually
In on time and signed for (“This is my own work”…….)
Total
A mark out of five that will contribute to the “homework” grade in the reports

8. Reactance, X, AND Capacitive Reactance, Xc
We measured the voltage across the capacitor (RMS value = 5.4 Volts) and we measured the RMS current “through” the capacitor (RMS value = 0.76 Amps)
We divided the voltage by the current and got a value in Ohms (7.1 Ohms) BUT this is not resistance. This is Capacitive Reactance. In a resistor, the energy is CONVERTED into heat energy. In a capacitor, the energy is temporarily stored and then given back.
The number of Ohms tells us the opposition to the flow of (AC) electrons but it is not resistance.

9. The Reactance of a capacitor is not a fixed value (unlike a resistor)
The Reactance of a capacitor is not a fixed value (unlike a resistor). Two things can alter the reactance.
The capacitance. If the capacitor has a huge value then it is easy for electrons to run off and on it and so this will reduce the Capacitive Reactance.
The frequency of the AC. If the frequency is zero (i.e. we have DC) then the Reactance of the capacitor will be infinite. If the frequency is infinite then the capacitor will never have any charge to generate a voltage.