Phy Practical Electricity Notes

Name:__________________( ) Class:___________ Date:__________ Practical Electricity: Worksheet 1 Have the right mindset: You are not supposed to understand everything the first time around. Care, perseverance and craftsmanship are what count Practical electricity 1. *Some uses of electricity (a) electric _heater_ eg : electric iron, electric stove, electric kettles. The heating elements are made of nichrome because of its high resistivity and high melting point. (b) electric _light_ eg: filament lamp and fluorescent lamp wire used to make the filament is tungsten. It has high melting point (34000C) (c) electric _motor eg: in fan, washing machine, hair dryer, blender. 2. *Measurement of electrical energy and electrical power Formulae: energy Power = time Therefore, 3. *Power ratings E = QV = Ivt = Ι2Rt = Rv2t P = tQV = IV = I2 R =Rv2 Criteria fro success: You can a) apply appropriate formula from the list to new situations b) explain the meaning of power rating c) Describe the 3 possible causes for danger of electricity. d) describe an a.c power supply Heating elements are usually marked with a voltage and power rating. Eg: A bulb has a voltage and power rating of 240 V, 100W. This means that the bulb dissipates_100_ J of

electrical energy every _1 second__ (100 W) if the p.d across it is _240 __ V. It will not dissipate 100 W if it the p.d across it is not 240 V. If the voltage across the bulb is less than 240V, then the bulb is dim and the power dissipated is less than __100_ W. If the p.d across the bulb is very much greater, then the bulb will glow brighter than normal and it may blow. 1 4. *Dangers of electricity There are three possible causes: a) damaged insulation b) overheating of cables; and c) damp conditions. 5. *Damaged insulation Insulating material derteriorate with time and use. If the rubber covering the live wire is damaged, the exposed wire can caused a severe electric shock to the user if the user touches it accidentally. This can lead to serious injury and even death. 6. *Overheating of cables The overheating of cables refers to the unusually large current flowing in the conducting wires under certain conditions such as short circuit or overloading. A short circuit can result when the live wire makes contacts with the neutral wire due to damaged insulation between them. This will produce a large current and the large amount of heat generated can melt the insulation and start a fire. 7. *Damped conditions If water touches the live wire, it provides a conducting path for a large amount of current to flow through it. 8. Electricity in the house + a) The electrical power is supplied by means of two cables. One is the live cable at an alternating voltage of +/-240 V and the other is the neutral cable + of a potential of 0 V. b) The electricity supply to homes is an _alternating_ current (a.c.) with a potential difference of 240 V. c) a.c: current that