Exercise 1. Put all possible questions to the following sentences

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There is always a disorderly movement of free electrons within all

substances, especially metals. Let us suppose that there is a movement of electrons through the wire, say, from point A to point B. What does it mean? It means that there is excess of electrons at point A. Unless there were a flow of electric current between A and B in any direction, it would mean that both the former and the latter were at the same potential. Of course, the greater the potential difference, the greater is the electron flow.

The electromotive force (EMF) is the very force that moves the elec- trons from one point in an electric circuit towards another. In case this EMF is direct, the current is direct. On the other hand, were the electromo- tive force alternating, the current would be alternating, too. The EMF is measurable and it is the volt that is the unit used for measuring it.

Current is unable to flow in a circuit consisting of metallic wires alone. A source of an EMF should be provided as well. The source under consideration may be a cell or a battery, a generator, a photocell, etc.

In addition to the electromotive force and the potential difference reference should be made here to another important factor that greatly in- fluences electrical flow, namely, resistance. All substances offer a certain amount of opposition, that is to say, resistance to the flow of current. This resistance may be high or low depending on the type of circuit and the ma- terial employed. Take glass or rubber as an example. The offer a very high resistance and, hence, they are considered as good insulators. Nevertheless,

one must not forget that all substances do allow the passage of some cur- rent provided the potential difference is high enough.

Certain factors can greatly influence the resistance of an electric cir- cuit. Among them there are the size of the wire, its length and type. The thinner or longer the wire, the greater is the resistance offered. Besides, silver wire would offer less resistance than an iron one.

Exercise 1. Put all possible questions to the following sentences

1. The excess electrons will flow towards the point of deficiency.

2. The parallel circuit provides two or more paths for current flow.