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Electricity

Electricity. N Bronks. E l e c t r i c c h a r g e. L i k e c h a r g e s r e p e l . O p p o s i t e c h a r g e s a t t r a c t. Electric Current. Note that electrons go from negative to positive. +. -. e -. e -.

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Electricity

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  1. Electricity N Bronks

  2. E l e c t r i c c h a r g e • L i k e c h a r g e s r e p e l . • O p p o s i t e c h a r g e s a t t r a c t .

  3. Electric Current Note that electrons go from negative to positive + - e- e- Electric current is a flow of negatively charged particles (i.e. electrons).

  4. Effects of Electricity Heating Effect Used in Kettles Irons Fuses Light Electromagnetic Effect (Current will Move a compass Needle) Used in Motors Loudspeakers Chemical Effect Used in Electroplating (Cutlery is Plated in silver To stop it Corroding)

  5. Basic ideas… Electric current is when negatively charged electrons start to flow around a circuit. We use an ammeterto measure it and it is measured in amps. We use the letter I (its latin) for current.

  6. Basic ideas… Potential difference (also called voltage ) is how big the push on the electrons is. We use a voltmeterto measure it and it is measured in volts, a unit named after Volta.

  7. Resistance is anything that resists an electric current. It is measured inohms ().

  8. Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter

  9. Components Cells as a battery Bulb Resistor – Reduces current

  10. Current Current will only flow in a complete circuit Electrical energy converted to light and heat

  11. More basic ideas… If a battery is added the current will increase because there is a greater voltage in the circuit If a bulb is added the current will decrease because there is greater resistance in the circuit

  12. Series Circuit

  13. Series Circuit -Parallel Circuit

  14. Series Circuit • Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.

  15. Parallel Circuit

  16. Parallel Circuit Here comes the current… Half of the current will go down here (assuming the bulbs are the same)… And the rest will go down here… A PARALLEL circuit is one where the current has a “choice of routes”

  17. Advantages of parallel circuits… There are two main reasons why parallel circuits are used more commonly than series circuits: • Extra appliances (like bulbs) can be added without affecting the output of the others 2) When one breaks they don’t all fail

  18. Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. Georg Simon Ohm 1789-1854 V Resistance = Voltage (in V) (in ) Current (in A) I R The resistance of a component can be calculated using Ohm’s Law:

  19. Measuring voltage and current Ammeter in series V Voltmeter in parallel A

  20. An example question: Ammeter reads 2A V Voltmeter reads 10V A What is the resistance across this bulb? V=I.R or R=V/I = 10/2 =5 

  21. Proving Ohm’s Law Ammeter reads 2A V Voltmeter reads 10V A

  22. Graph • Draw a graph of the results I /amps • The straight line proves OHM’S LAW V/volts

  23. Wiring a plug 1. 4. 5. 2. 6. 3. Earth wire Live wire Fuse Neutral wire Cable grip Insulation

  24. Fuses An electric fuse is a device which is used to limit the current in an electric circuit. The fuse safeguards the circuit and the electrical appliances from being damaged.

  25. Fuses The fuse wire is generally an alloy of lead and tin. It has a low melting point and breaks the circuit if the current exceeds a safe value. It is connected in series in the beginning of the electric circuits.

  26. Fuses Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break (melt) the _______ and protect the appliance and user from further _____. Words – large, harm, safety, melt, live, circuit, fuse

  27. Other safety devices… 1) Earthing Connecting any metal parts of a device to the ground means that if there is a fault the live wire does not come in contact with the user 2) Circuit Breaker This will break the circuit if too much current is detected. It can be reset.

  28. Electrical Safety The casing touches the bare wire and it becomes live • A combination of fuse and Earth The fuse will melt to prevent electrocution and the electricity is carried to earth That Hurts! OHP A.C. Supply

  29. DC and AC V DC stands for “Direct Current” – the current only flows in one direction: Time 1/50th s AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 240V T V

  30. The National Grid Step up transformer Step down transformer Homes Power station If electricity companies transmitted electricity at 240 volts through overhead power lines there would be too much energy lost by the time electricity reached our homes. So if we have a high voltage we only need a small current. We loss much less energy

  31. E l e c t r i c P o w e r • K i l o w a t t - H o u r s

  32. Cost per Hour of Electrical Goods • Where on the cost line would these go? • Computer, washing machine, hair dryer, Wii, Tumble dryer, phone, iPod and electric fire. 1c/hr €1/hr

  33. Cost of Electricity • A kilowatt-hour is the amount of energy used when 1 kW is used for 1 hour. • It is also called a unit of electricity. • At the moment it is about 11c.

  34. Electricity Bills Example 1 What is the cost of running a 2.5kw heater for 5hrs if a unit costs 10.5c? For 1 hour the cost is 2.5x10.5=26.25c And for 5hours 5x26.25 =131.25c

  35. Electricity Bills Example 2 What is the cost of running a 0.15kw TV for 2hrs if a unit costs 10c? For 1 hour the cost is 0.15x10=1.5c And for 2hours 2x1.5 =3c

  36. Electricity Bills Example 3 What is the cost of running a 1.5kw dishwasher for 1.2hrs if a unit costs 10.5c? For 1 hour the cost is 1.5x10.5=15.75c And for 1.2hours 1.2x15.75 =18.9c

  37. H/W • P371 • 34.15

  38. What is an electromagnet? • Electromagnet – a magnet made from a current bearing coil of wire wrapped around an iron or steel core.

  39. Chemical Effects of an Electric Current • Electrolysis is the chemical effect of an electric current • Voltameter consists of electrodes, an electrolyte and a container

  40. Chemical Effects • Uses • Electroplating to make metal look better, prevent corrosion • Purifying metals • Making electrolytic capacitors

  41. Diode as Valve • Only allows current in one direction

  42. Diode as Valve • Only allows current in one direction Forward Bias Reverse Bias

  43. LED • An LED (Light Emitting Diode) works in the same way. We use it for pin lights. Forward Bias Reverse Bias

  44. Light Dependent Resistor LDR • Resistance decreases when light shines on it • Used to turn on street light

  45. H/W • P369 • Q 34.1,34.2,34.3,34.4,34.9 and 34.14

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