# UK Amateur Radio ## Foundation Licence 2002
### Technical Basics Part A
Most of what you need to understand about electricity begins with the 'electron' and it is the way electrons move and respond that gives rise to virtually all the basics you need to understand. Think of the electron as minuscule hard ball with an negative 'electric charge' - this charge means it is attracted to anything with a positive electric charge and repelled by any thing with a negative electric charge. Electrons can move around quite easily in some materials which are known as 'conductors' but can hardly move at all in some other materials known as 'insulators'. To make things work you need a source of these electrons, such as a battery. A battery has a lot of electrons at one terminal - the negative terminal which want to flow to the positive terminal. They can only do this if you provide a path using a 'conductor' which is usually a bit of wire. The flow of electrons constitutes an electric current or just a current.
### Simple circuit theory | We will now look at a simple circuit using a battery, some wire, and a bulb to make the electrons do something useful.
| So far I have used the term 'battery' as it should be familiar to you. However, strictly speaking a 'battery' like that on the left should be called a 'cell' and a battery is really a number of connected cells. Try to remember this in future but don't loose any sleep over it! The cell opposite is a 'primary' cell, it cannot be recharged, it has a terminal voltage of approx 1.5V
There is nothing particularly special about the cell that I have photographed it is just one that I happened to have around and its terminal voltage is approx 1.5V. You will note that the top has a slight dome to it but the bottom is generally flat. The domed top of the battery is the POSITIVE connection and the bottom is the NEGATIVE connection. NEVER directly link the top of a battery to the bottom else damage or fire could result.
### EXPERIMENT no.1 Move mouse onto the picture to close the switch NOTE: the electrical circuit is not made until the "switch" makes contact. The positive + end of the "battery is marked with a red strip whilst the negative end of the "battery" - is marked with a black strip. | The picture on the left shows a very simple circuit. The battery (made up of two cells) is the source of electrons which can move along the wire, through the bulb, and switch (if it is 'on') and get to their destination at the other terminal of the battery. When the switch is closed, a current flows and the bulb lights. The circuit is said to be "made". When the switch is open the circuit is said to be "broken" and the bulb goes out. The filament bulb is really just a special conductor which gets very very hot when enough electrons are flowing through it. It get so hot that it glows and emits light. The power is dissipated as both heat and light.
If you try this experiment at home ensure that the battery and bulb are the same voltage or else enough electrons will not flow to make the bulb glow brightly or too many may flow and the filament inside of the bulb will get so hot it burns out. ### Conventional current flow In the past you may have learned the convention that an electric current flows from the positive terminal to the negative and was later named the conventional current. This was a mistake made many years ago that we now must live with. The electrons actually flow from the negative terminal to the positive terminal but we pretend that the current flows from positive to negative so as not to embarrass the old boys who made the mistake all those years ago! ### Direct Current In the case of this experiment electrons are only flowing in one direction and we refer to the current flow as being direct or more normally as DIRECT CURRENT or DC. The symbol for current flow is I and we measure current flow in AMPS, usually abbreviated to A. A single cell or a battery can only provide a Direct Current. The greater the volts the great the current that can flow assuming the load resistance is constant and does not change..
### How and why these electrons move If you have a lot of electrons in one place that want to move to another - such as from the negative terminal of a battery to the positive terminal - then the terminals are said to have a POTENTIAL DIFFERENCE between them. Think of this as the 'potential' for a current to flow. The more electrons that want to make the journey the larger the POTENTIAL DIFFERENCE. The symbol for a POTENTIAL DIFFERENCE is V. We measure it in Volts, symbol V. The only way the electrons can move is if we provide a 'path'. In the example above the path is the wire, the switch and the bulb. Not all conductors let electrons make the journey easily and they are said to 'resist' the movement of the electrons. We refer to this as RESISTANCE, for which the symbol is R and we measure resistance in OHMS, usually written as .
In this experiment, when the battery has been in use for sometime the internal resistance increases as the Potential Difference drops under load conditions. The battery is said to be flat.
So what have we learned so far If you have a lot of electrons in one place - such as at one terminal of a battery - they want to move to the other terminal when an external circuit exists. The terminals of a battery have POTENTIAL DIFFERENCE as there are electrons at one wanting to reach the other. The symbol for POTENTIAL DIFFERENCE is V and we measure it in VOLTS, V If we provide a path for the electrons to move along we get a flow of electrons we refer to as a CURRENT. The symbol for a current is I and we measure it in AMPS, A Certain materials resist the flow of electrons and we refer to this feature as RESISTANCE. The symbol for resistance is R and we measure it in OHMS, . When the electrons only flow in one direction we refer to the current as being a DIRECT CURRENT. or DC. A battery can only supply DIRECT CURRENT (DC).

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