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What we will do What we will learn 13Px 15 Mahuru 2017

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Presentation on theme: "What we will do What we will learn 13Px 15 Mahuru 2017"— Presentation transcript:

1 What we will do What we will learn 13Px 15 Mahuru 2017
Preliminaries and roll How to kick off well Revisit why capacitors let AC through but don’t let DC through and out why Why a capacitor permits AC Revisit the new concept: reactance What it is PLUS how it is both similar to and different from resistance Revisit 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 HRT, HW help and HW marking How to make it to the 20th of November on time

2 Today is Ushil’s birthday
Important Notice Today is Ushil’s birthday

3 HW item Skills practiced Elex: Pages 193 - 194
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. Elex: Pages Due Monday, the 25th of Sept 2017 Reactance for AC in capacitors Elex: Pages 213 Reactance for AC in inductors

4 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

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9 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.

10 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.

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