1. Society has become increasingly dependent on electricity over the last 200 years What do you know about the debate that took place between Volta and Galvani about animal and chemical electricity? How did it contribute to increased understanding about electricity? How have the main sources of domestic energy have changed over time? What are some of the impacts of changes in, and increased access to, sources of energy for a community? What are some of the ways in which electricity can be provided in remote locations?
2. One of the main advantages of electricity is that it can be moved with comparative ease from one place to another through electric circuits Behaviour of electrostatic charges and the field associated with them + - - Do you know what a millicoulomb and microcoulomb are? prefixes? sci. notation? + + + -
Describe the electric field as a field of force with a field strength equal to the force per unit charge at that point: E =F/q F = q. E + - 200 V 700 V F = mg 1. Which is the positive plate? 2. What direction would the electric field be? 3. Is this particle positively or negatively charged? 4. What two forces act on a charged particle between the plates? Equations? Direction? 5. How can we change the strength of the field?
Current is the rate at which charge flows (C/s or amperes) under the influence of an electric field Current can be either direct with the net flow of charge carriers moving in one direction (D. C. ) or alternating with the charge carriers moving backwards and forwards periodically (A. C. )
Potential difference (voltage) between two points is the change in potential energy per unit charge moving from one point to the other (joules/coulomb or volts) Discuss how potential difference between different points around a circuit varies 10 A 12 W R 1 240 V R 2 R 3 8 W 4 W
b Conductors have electrons in their atoms which flow easily b Insulators have outer electrons in their atoms which do not flow easily
Solve problems and analyse information applying V = IR 10 A 12 W 240 V R? 8 W V = IR VT = IT. RT RT = VT / IT = 240/10 = 24 W R = 24 - 12 - 8 = 4 W
q 3. Series and parallel circuits serve different purposes in households 10 A 12 W R 1 240 V R 2 4 W R 3 8 W • Resistors on one branch of circuit • Total resistance RT = R 1 + R 2 + R 3. . . • Current is the same for each of resistors in series • Voltage drops vary - use Ohm’s Law
10 A 240 V R 1 R 2 R 3 • Resistors on different branches of circuit • Total resistance: 1/RT = 1/R 1 + 1/R 2 + 1/R 3. . . • Voltage is the same for each of resistors in parallel • Current may vary - use Ohm’s Law
A Ammeter always connected in series to read current THROUGH the resistor V Voltmeter always connected in parallel to read voltage ACROSS the resistor
Explain why there are different circuits for lighting, heating and other appliances in a HOUSE b IF ONE CIRCUIT BLOWS, THE OTHERS DON’T b THE MAIN DIFFERENCE IS HEAVIER GAUGE WIRING IN POWER POINT AND HEATING CIRCUITS (MORE CURRENT) b IT FOLLOWS THAT POWER POINT AND HEATING CIRCUITS HAVE LARGER CAPACITY FUSES AND CIRCUIT BREAKERS
4. The amount of power is related to the rate at which energy is transformed
What are the advantages and disadvantages of labelling goods with power rating? Why has a simple scale has been used for energy rating on commercial goods and how do these scales relate to potential difference and current? Propose reasons as to why the kilowatt-hour is used to measure domestic electricity consumption rather than the joule You gathered first-hand information to estimate the cost of electricity consumed by your household Discuss ways in which consumption could be reduced
5. Electric currents also produce magnetic fields and these fields are used in different technologies in the home Describe the behaviour of the magnetic poles when they are brought close together The direction of the magnetic field at a point is the direction of force on a very small magnetic pole when placed at that point Describe the magnetic field around single magnetic poles and pairs of magnetic poles Compare the nature and generation of magnetic fields by solenoids and a bar magnet What was involved in these experiments?
Describe the production of a magnetic field by an electric current in a straight current-carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines B I B B
Assess the impact of applications of magnetic fields on society Explain one application of magnetic fields in households, such as: telephone or stereo speakers magnetic tape and use the available evidence to assess the impact of its use
6. Safety devices are important in household circuits Discuss the effects of an electric shock from both a 240 volt AC mains supply and various DC voltages, from appliances, on the muscles of the body p. 133 -134 Jacaranda text SEE Identify the functions of circuit breakers, fuses and other safety devices in the home How are insulators and earth wires used in appliances?
Скачать презентацию 1 Society has become increasingly dependent on electricity
dc6eb21868499c31db2b8cefb098fe2c.ppt