Text 4. Branches of electricity

The study of electricity may be divided into three branches: magnetism, electrostatics and electrodynamics. Magnetism is the property of the molecules of iron and some other substances to store energy in a field of force. Electrostatics is the study of electricity at rest. Rubbing glass with silk produces static electricity. Electrodynamics is the study of electricity in motion, or dynamic electricity. The electric current which flows through wires is a good example of the latter type of electricity.

This flow of electricity through a conductor is analogous to the flow of water through a pipe. A difference of pressure at the two ends of the pipe is necessary in order to maintain a flow of water. A difference of electric pressure is necessary to maintain a flow of electricity in a conductor. Different substances differ in electrical conductivity because of the ease with which their atoms give up electrons. Electrical energy has intensity and quantity. Instruments have been devised which can be used to measure it in amperes and volts.

TEXT 5. WHAT IS AN INTEGRATED CIRCUIT?

What is an integrated circuit?

An integrated circuit is a complete circuit capable of doing the same job on an input signal as a discrete circuit containing a large number of active and passive components on a printed circuit board. What makes the difference is that in the case of an integrated circuit the whole circuit is one component, formed in one set of operations on a single chip of silicon such as is used to make a single transistor. The important point is that the integrated circuit is made in the same way as a single transistor, using the same type of operations, and that all the connections in the circuit are formed at the same time as the other parts of the circuit. The most important difference between an integrated circuit and discrete circuit is that the integrated circuit is very much smaller. This is often an advantage because it means that we can put integrated circuits into containers which we had never before thought could contain electronic circuits, so that we have, for example, pocket electronic calculators.

Another important point is that, because an integrated circuit is made in the same way as a transistor, it can often be made for practically the same price as the transistor. But one integrated circuit can carry out the task of several hundred transistors.

A third factor is reliability. Instead of gathering together several hundred components, testing them, soldering them into a printed circuit board, we have one component to test and to mount. No single part of the integrated circuit should be less reliable than the other parts, since it was all made in one piece. In this way we can gain tremendously in reliability since the only connections to be made are these to and from the integrated circuit.