* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Mains electricity - Thomas Tallis Science Department
Ground loop (electricity) wikipedia , lookup
Electrical substation wikipedia , lookup
Electrical ballast wikipedia , lookup
Current source wikipedia , lookup
Fuse (electrical) wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Electrification wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Power engineering wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Opto-isolator wikipedia , lookup
Utility frequency wikipedia , lookup
Telecommunications engineering wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Three-phase electric power wikipedia , lookup
Skin effect wikipedia , lookup
History of electric power transmission wikipedia , lookup
Buck converter wikipedia , lookup
Overhead line wikipedia , lookup
Voltage optimisation wikipedia , lookup
Surge protector wikipedia , lookup
Portable appliance testing wikipedia , lookup
Single-wire earth return wikipedia , lookup
Stray voltage wikipedia , lookup
Ground (electricity) wikipedia , lookup
Rectiverter wikipedia , lookup
National Electrical Code wikipedia , lookup
Electrical wiring in the United Kingdom wikipedia , lookup
Mains electricity wikipedia , lookup
Mains electricity Revise the following • • • • • Direct and alternating current 3-pin plugs and electrical cable Safety – fuses and earth wire Period and frequency (Higher tier) Calculating Power Direct current Alternating current What are the parts of a plug? earth terminal live terminal fuse neutral terminal cable cable grip Label the plug parts The names and jobs of each plug part What’s inside an electrical cable? copper insulating plastic • An electrical cable contains three wires. • These wires are made of copper because it is a good conductor of electricity • Each wire is made of thin strands of copper to keep the cable flexible • Each wire is encased in plastic to stop the wires touching and causing a short circuit • Plastic is used as it is a good insulator, as well as being tough and flexible • The whole cable is encased in another layer of plastic What does each wire do? The live wire (brown)carries a current that alternates between a negative and positive voltage. The earth wire (green and yellow) is a safety wire that is needed to earth appliances with a metal case. This makes it safer to touch the appliance if it develops a fault. The neutral wire (blue) completes the circuit. It is kept at a zero voltage by the electricity company. Safety using Fuses and Earthing FUSES • • A fuse contains a thin wire, which melts if the current is too high. This breaks the circuit and so electricity is unable to flow through the appliance. • The appliance stops working and any danger has been averted. • Fuses act as an early warning system, preventing appliances from being damaged by surges in electricity and warning owners of faults. EARTHING • Cables contains an earth wire to provide an alternative path for current if appliances develop faults. • An earth wire is essential for an appliance with a metal case. • If the live wire becomes loose and touches the metal case, a very large current flows to earth and blows the fuse, breaking the circuit • When an appliance is working correctly, no electricity flows through the earth wire. Frequency and period (Higher tier) • We can use an oscilloscope to work out the frequency of the ac supply by measuring the period (time taken for one complete cycle) • Frequency and period are connected by the equation: Frequency (Hertz) = 1 . period (seconds) Using oscilloscope traces to work out period and frequency Each division will have a potential difference (voltage) value Zero voltage (0V) The 0 voltage represents the Neutral terminal (stays at a potential close to zero – compared to the Earth) Time Work out the frequency of the supply shown below? Each time division =1 milliseconds Period = 4 divisions x1 = 4ms 4 ms = 0.004 seconds Frequency = 1/Period (seconds) Frequency = 1/0.004 = 250Hz Calculating Power • Electric current is the rate of flow of charge. • When an electrical charge flows through a resistor, electrical energy is transformed into heat energy. • The rate at which energy is transformed in a device is called the power. Power = current x potential difference (Watts/W)) (Amps) (Voltage/V)) energy transformed (Joules/J) = potential difference (Voltage/V) charge = current x (Coulomb/C) (Amps) x charge (Coulombs/C) time (secs)