Si units for electricity

Electrical Quantity	Symbol	Definition	SI unit	Abbre-viation
Electric current
Voltage
Resistance
Electric(al) power

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.

amps resistance conductor voltage R supply components circuit ohms I wattage watts current volts E

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.