13 BEST MAJOR

In our BASIC ELECTRICITY we have experince how to connect wires and how to make wire connections without being shortcircuit. Diagram number 1 illustrates an extremely simple circuit. (For the moment, ignore the dotted line and the points A and B). The battery is represented by 4 lines (the longer line being positive and the shorter one negative). Starting from the negative end of the battery, electrons "circle" through one wire, pass through the light bulb, pass through the other wire and then return to the battery thereby completing the circuit. See? Quite simple.

This is all well and good but there are 2 drawbacks to this circuit 1) the light always stays on and 2) the power is constantly being used. How can we turn the light bulb 'off'? Well, we could unscrew the bulb from the socket but in the real world this is very inconvenient. (Light bulbs are inside fixtures, on ceilings and so on). Perhaps we could disconnect the power at the source. This too is very inconvenient. You would have to go down to your basement to shut the power off. Or - much more dangerous - you would have to disconnect the electrical supply wire before it reaches the light socket.

Is there a safe way to interrupt the electron flow without physically touching the wire? Sure. It is called a SWITCH !!!

The inside of a typical household wall switch has a strip of metal (B), making contact with point 'A', completing the circuit and thereby conducting electricity to the light. This would obviously be the 'ON' position. When the insulated lever is moved down to the 'OFF' position, it pushes the metal strip away from point 'A', breaking the circuit and turning the light 'OFF'.
This type of switch (having a lever which "flips" it on and off) is called a toggle switch.

Referring to Diagram 2, the wiring is very similar to Diagram 1 except a switch has been added. Compare this to the Typical Household Light Switch diagram. Pretty much the same principle at work wouldn't you say? This type of switch is a Single Pole Single Throw (or SPST). This means that it controls one wire (pole) and it makes 1 connection (a throw). Yes, this is an on/off switch, but a 'throw' only counts when a connection is made. 'Off' is not considered a 'throw'. Also notice that only 1 wire has to be switched. (Following the circuit from one end of the battery to the other you can see why this is so).

As it is, this circuit alone could be your science project. A variation could be substituting a push-button switch and putting a 'buzzer' or 'doorbell' where the light is. Now you have a good demonstration of how a doorbell is wired. Pushbutton switches are usually "momentary on"."momentary off" pushbutton switches, but using one in a doorbell circuit would mean the bell would be constantly on until someone pressed the button. Impractical don't you think? That is to say the connection is made only when you press the button. There are "momentary off" pushbutton switches, but using one in a doorbell circuit would mean the bell would be constantly on until someone pressed the button. Impractical don't you think?