Unit 8a Book

As a student of electrical engineering, you probably understand how and why electricity is so important for us. Without electricity, our lives would certainly be different and perhaps even more difficult. Electricity powers lots of machines that make our lives easier. What are the most important discoveries and inventions in the field of electrical engineering? Read about some of them, shortlisted by the server interestingengineering.com. As you read the text in this task, put the deleted subheadings in their original places in the text. After you finish, leave the task window open because you will need the information from the text to complete a follow-up task.

Now let´s change the subject for a while. What do you think: are we alone in the Universe? Or are we just one of the many species, which means that we are likely to meet some extra-terrestrials? If so, the question is why they haven´t contacted us before. Maybe it is because they are more technologically developed than us. This is the idea some Hollywood movies try to persuade us to believe. And in fact, this is quite logical: even we, humans, would not be very interested in having a chat with someone less developed, for example, ants. Now imagine these extra-terrestrials are planning to contact us. To be a hundred percent sure it is the right time to do that, they have a special check list. Now, they are judging our technological development by discussing some individual key discoveries and inventions to see whether or not they have been made on Earth. One of the questions may be, for example, as follows:

Have the humans discovered electricity?

And the answer would be:

Yes, they have. Electricity was known to Ancient Greeks and Romans, but they were not able to use it. But it has been studied scientifically since the 1700s.

The key discoveries/inventions are listed in the previous task and in this follow-up task. Complete all the gaps in this task, and as you do so, pay special attention to the use of two verb tenses: the Past Simple (active and passive) and the Present Perfect (active and passive).

How successful were you at completing the task? While doing the task, you may have noticed that basically you use the Present Perfect Tense if you want to talk about actions that started at an unspecified past time and are still continuing. When using the Present Perfect Tense, you usually give some general kind of information, without going into details:

Yes, they have discovered DC current. (has/have + past participle)

You can also convert the active voice into the passive voice especially if you wish to sound more formal and do not want to mention the agent (i.e. the one that does the action). The object of the active sentence then becomes a subject of the passive sentence:

Yes, DC current has been discovered. (has/have been + past participle)

If you add some details, especially about the time of the discovery, you need to use the Past Simple tense:

Direct current was first produced artificially by Alessandro Volta in the early 1800s.

(was/were + past participle)

The reason why you need to use the Past Simple tense is quite obvious: the action is finished. There is no longer the year 1800 or the 1800s.

Both the tenses, the Past Simple tense and the Present Perfect tense have already been covered (the Past Simple tense in the AEL3 course in Unit 1a and the Present Perfect tense in Unit 3a). The passive voice was covered in the same course in Unit 2bc. However, if you feel you need to revise them in detail, click the links in this paragraph. After brushing off your knowledge, practise the Past Simple passive and the Present Perfect passive here and here.