Electrical PowerThe amount of current, in amps, required by an electrical appliance – such as a TV or an electric kettle – depends on the power of the appliance. This number, expressed in watts (W), will be marked somewhere on the appliance. To calculate the required current, simply take the wattage and divide it by the voltage of the electrical supply in your home (from ‘Professional English in Use. Engineering’).
Exercise 19. Solve the clues and complete the puzzle with the terms from the text above. 1. another term for amperage 2. provided by a battery, for example 3. measured as a wattage 4. allows current to flow through it 5. has very high electrical resistance 6. carried by moving electrons 7. another term for an electrical ‘device’ 8. the consequence of a person touching a live conductor
ELECTRIC(AL)
Exercise 20. Match the terms in the box with the appropriate definition.
1. __________ – the flow of charge between two points caused by voltage or electric field. 2. __________ – substance that allows heat or electricity to pass through it. 3. __________ – the ability of something to stop the flow of electricity. 4. __________ – the unit of electric current, a flow of one coulomb per second. 5. __________ – the unit for power (the rate of transfer the energy), the name given to a rate of one joule (one Newton meter) per second. 6. __________ – a unit used for measuring electrical resistance. 7. __________ – the amount of power in an electric current, measured in volts. 8. _________ – direct current motor that drives an alternator, or any other system that converts input DC to AC. 9. _________ – a continuous electric current that flows in one direction only, without substantial variation in magnitude. 10. _________ – a continuous electric current that periodically reverses direction, usually sinusoidally. 11. __________– substance with low conductivity for the energy transfer. 12. _________ – metal sample drawn into a long uniform thread. 13._________ – voltage electromagnetic machine used in alternating current contexts whose design output tends to be at a different voltage from the input. 14. _________ – machine with a mechanical input and an electric output. 15. _________ – a linked set of one or more electric (electrochemical) cells. 16. _________ – a transformer that increases the voltage. 17. _________ – a transformer that decreases the voltage.
Exercise 21. Complete the table below with appropriate information. SI units for electricity
Exercise 22. Complete the sentences about electric current with one or two words. 1. An electric current is the flow of __________. 2. In a metal, an electric current is the flow of _______________. 3. An electric current can flow through a __________. 4. An electric current cannot flow through an __________. 5. The electric current gets smaller with a larger __________. 6. An electric current has the unit __________. Exercise 23. Complete the extract about current and power calculations using the words in the box.
In electrical calculations, electromotive force is expressed by the letter ____, resistance by the letter ____, and current by the letter ___ (which comes from the word ‘intensity’) According to Ohm’s law: I=E/R. in other words, the ________ flowing through a _________ measured in _____, equals the ________ of the electrical _________, measured in _____, divided by the total ___________, measured in _____. To work out the value of R, it is necessary to calculate the total resistance of all the __________ and connecting length of ___________ that make up the circuit. Once both the voltage and amperage are known, it is possible to work out the power, measured in _____, that will be consumed. Power (P) can be calculated using the equation P=EI. Therefore _________ equals voltage multiplied by amperage. Exercise 24. Choose the correct answer. 1. A current is said to exist whenever _____. a. a wire is charged c. electric charges are unbalanced b. a battery is present d. electric charges move in a loop 2. Current has a direction. By convention, current is in the direction which ___. a. + charges move b. - electrons move c. + electrons move 3. What type of current is electricity from the mains? a. direct current b. alternating current c. Both Ac and DC 4. Which of the following is a way to increase an induced current? a. move the magnet more slowly b. use a weaker magnet c. move the magnet more quickly 5. What is a transformer? a. a device that will produce a current b. a device that can change a current c. a device that will transfer electrical energy to light energy 6. Why is the voltage increased in the national grid? a. it is the only way the current will flow through the wires b. houses can only use electricity at this voltage c. less energy is wasted that way 7. What type of transformer converts the voltage as it comes into the home? a. step-up b. transferring c. step-down Exercise 25. You should know the difference between direct current and alternating current. Using the text above and you knowledge of electric current complete the table of comparison with appropriate information. Two diagrams that show the oscilloscope screens displaying the signal from an AC supply and a DC are given under the table. Choose the corresponding one for each type of current.
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