CHAPTER 22 Electric Circuits

• Distinguish between static electricity and the types of current electricity.
• Describe the models and theories of electrical conduction in metals, aqueous solutions, liquids and gases.
• Recall the factors that affect the current flow through various conductors.
• Define electrical resistance, electrical potential difference, voltage, electrical energy and electrical power.
• Recognise the common electrical symbols used to draw circuit diagrams.
• Describe the method of construction, method of connection and types of electrical circuit measurement meters commonly used.
• State the mathematical form of Ohm's and Kirchhoff's electrical circuit analysis laws.
• Recognise the difference between series and parallel connections of both circuit components and sources of EMF.
• Explain the basic operation of domestic electrical energy supply and the dangers associated with mains electricity.

Scientific Processes

• Gain experience with reading electrical circuit diagrams and wiring basic DC circuits.
• Identify the correct measurement meter to use in the analysis of electrical circuits.
• Predict using graphical techniques and calculation, such unknown quantities in electrical situations as voltage, current or resistance.
• Use correct circuit symbols to draw an operating electrical circuit.
• Calculate electrical energy used, given data tables or graphical displays of the power of an electrical device, time of operation and typical energy costs.

Complex Reasoning Processes

• Derive and apply equations for electrical quantities, including amount of charge, resistance, voltage, current, energy and power.
• Be able to analyse complex DC circuits qualitatively and quantitatively including applications of Ohm's law and Kirchhoff's laws.
• Select relevant properties of electrical circuit systems in order to predict its behaviour or output under a given set of conditions.
• Propose reasons for electrical accidents in household applications and be able to advise on typical safety precautions.
• Outline a method for carrying out an electrical energy audit for a household.

CHAPTER 22 SUMMARY

• Metals are good electrical conductors because they contain loosely bound valence electrons in their outermost atomic electron shells.
• Charges in motion may involve electron movement, electrolytic ion movement or gaseous ion movement.
• Electrons move through conductors with a typical drift velocity characteristic of the conductor type.
• Electric current flow in circuits may be modelled using a water flow analogy.
• Electric current flow may involve DC or AC waveforms and can be described as either conventional (positive) current or electron (negative) flow.
• The electromotive force (EMF) of a battery is the energy transferred per coulomb of charge within the battery. EMF is measured as a voltage in volts.
• Potential differences within a circuit are referred to as a potential rise when produced by an EMF source or a potential drop when caused by a load element. Potential differences are also measured in volts.
• Potential differences in nervous impulse transmission throughout the body are called action potentials.
• Resistance is the opposition to the flow of electric current through a conductor and is measured in units called ohms. It is defined as the ratio
• Sources of EMF (voltage) such as batteries have internal resistance which produce an effective terminal voltage.
• Resistive elements or sources of EMF may be connected in series or parallel configurations.
  R_TOT = R₁+ R₂. or 1/R_TOT = 1/R₁ + 1/R₂.
• Electrical circuit meters are called ammeters and voltmeters, and are primarily based on the simple galvanometer.
• The three important electrical circuit laws which allow detailed analysis are called Ohm's law, Kirchhoff's junction law and Kirchhoff's loop law.
• Electrical power, measured in watts, is the rate at which electrical work is done in a circuit and can be calculated using P=W/t
• Appliances in common usage have a power rating, an energy efficiency rating and use electrical energy in units called kilowatt-hours.
• Common electrical wiring standards and colour codes are used by electricians licensed to install and repair household electrical appliances.
• Electrical safety devices and personal responsibility are both important in the continuing safe use of electrical energy.
• Electrical effects on the human body may ultimately lead to electrocution and death without appropriate knowledge and understanding.

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