Frequency
The number of cycles per second is the frequency of an a-c. There are two frequencies: the standard for Europe is 50 cycles per second while the standard for the USA is 60 cycles per second. A standard frequency has a great advantage since different systems can be interconnected.
39 3
Ask each other questions covering the text.
Electronic Control of Motors
It is necessary to control motors. That is, motors must be started, stopped, and reversed, and, within limits, it must bej possible to control their speed.
The controls needed to perform these various functions on d-c motors are designed to alter the quantity or the direction of the current in the field or in the armature of the motor. On d-c controls, these functions were shown to consist mainly of resistances, switches, and solenoids.
It is possible to control motors, not only electromechanically an-d electromagnetically, but also electronically, by means of vacuum tubes or gas-filled tubes. Some electronic devices can be made to operate a relay which in turn controls a motor. Others influence the amount and direction of current flowing in the motor circuit and thus the action of the motor itself. Both types may be found in one control device.
40 3
Work in pairs. Dwell with your fellow-student on basic elements of automation. Use ex. 19, 20, 37, 39.
41 35
Home exercise. Pick out all the sentences with Infinitive and translate them. Be prepared to dwell on the science of the future.
Science of the Future
Alf: I can’t understand what made you buy such an expensive electronic computer!
Eric: I didn’t buy it. I got my father to do it.
Alf: Really?
Eric: The other day we went to see an exhibition of various devices of
that kind and when my father saw a computer wash the dishes, peal potatoes, sweep thq floor, scratch somebody’s back, and what not, he was thrilled to pieces, and had the makers send one to our flat at once.
Alf: It must have been a sight worth seeing, I suppose.
Eric: I don’t want you to get so excited, but it’s really marvellous. When I come to think what brain-work went to its making, and how well off some brainless people can be, I really begin to think I ought to have taken up electronics.
Alf: You seem to have forgotten how bad you were at mathematics when you were at school...
Eric: Now, that Eve got the computer, I can be taught mathematics or any other subject in no time, and if I’d had one at school I would have
been taught everything practically with no effort at all!
Alf: Do you mean to say you want the electronic computer to teach you how to work?