Two main types of circuit connection

When electrical devices are connected so that the current is not divided at any point, they are said to be connected in series. Let us picture two lamp bulbs connected in such a manner. Then the wire enters at one side of the socket and leaves it at the other. All the current that flows through the first bulb in one second must also flow through the second bulb in one second. Undoubtedly, under such conditions, the current in every part of a series circuit is the same.

If the current is passed through two lamp bulbs, they will not be so bright as when only one of them is in the circuit, at least, their brightness will be dimmed to a considerable extent. It is because in a series circuit the total resistance equals the sum of all the separate resistances.

Series circuits are usually automatically controlled so that the current is kept constant regardless of the voltage.

There are, undoubtedly, several advantages in using lamps in series. Namely: 1. A number of low-voltage lamps can be connected to a high-voltage circuit. 2. But one wire is required from lamp to lamp. 3. Most important is the saving in wire material. The chief disadvantages are that all the lamps must burn at the same time and, in addition, it is dangerous to handle the lamps when the current is on.

A series circuit is by no means the only possible way of circuit connection. In ordinary house lighting, for instance, lamps are connected in parallel, each lamp filament representing an independent path (or branch) from the minus main wire to the plus wire.

As a matter of fact, in everyday electric work we often deal with circuits where the current branches between two or more paths.

When a circuit is divided in such a way that part of the current goes through one branch and part through another, it is called either a parallel, or a shunt, or a multiple circuit. In such a case, if we turn on the light in one room, we may see that both bulbs light it brightly. Provided one of the bulbs is unscrewed and removed, the second will continue burning as brightly as before. Doubtless, that is unlike the series circuit.

In parallel circuits the total current is equal to the sum of all the currents that are passing through the branches of that given circuit.

Each branch of a shunt circuit may or may not have the same resistance as that of another branch. If both of the resistances are lamps of equal size, theresistances will be equal likewise. Computing resistances in the above circuit, we may apply Ohm's Law provided we 'know both the total voltage and the total amount of the current provided.

In series circuits one should add resistances while in shunt circuits it is necessary to add conductances and invert the sum to obtain the total resistance.