Technical Basics I

Units and Symbols.


Unit Symbol
Current I Amp (A) Current is made of units called electrons, the bigger the current required the bigger the transport needed *Bigger wire
Potential Difference V Volt
Resistance Ω (R) The measurement of how Electrons get restricted by components

From these you can work out the value and power consumption of anything.

*Of the Record Advice. You need to remember Ohms Law (Power Triangle) in the exam you can write it on a blank piece of paper so that you can use it.


I   R

and if you find that hard to remember remember VIRUS! its a good little clue.


All measurements are in metric. For more on metric units look here *Not for the faint of heart, but I’ve never ever used half of those units


a metre (m) being 100cm (cm) written as 0.01.  Below that we have the millimetre, 1000mm (mm) or 1000th of a m written as 0.001


a 1000 metres (m) is written as 1km and likewise is also 1,000,000m written as 1Mm note a Megametre starts with a capital, thus is written in shorthand as


So we need to know and understand mm, cm, m, km and Mm These are also used for measuring units of electricity.



Whilst the “Foundation Now” book shows the picture to the right as a battery in fact it is not it is a single cell, multiple cells go to produce a 9v battery. However you do need to know the symbol.

a cell, component of a battery

a cell, component of a battery


A lamp or Bulb

The Next symbol we need is the symbol for a bulb again in the case of the book is a bulb, that is to the left.

Now with these components by wiring them together we can make the lamp light The battery provides the power (V) to the lamp, this flows from the positive terminal of the battery to the negative. if there is a break in the wire connecting the two the circuit will not be complete and the light will not shine. The bulb has a wire, inside called a filament, which glows when the circuit, see the diagram of the circuit below.

Basic Battery / Cell and bulb

Basic Battery / Cell and bulb

The Same design with a resistor

The Same design with a resistor



A resistor basically skims of some of the current and turns it into heat. In the same way the element in your kettle or electric fan heater works. So a small resistor will have limited effect on the brightness of the bulb but the more the resistor is resistive (higher value) the dimmer the bulb will be. so a 1Ω resistor will have little effect whilst a 1MΩ will make sure no power gets to the bulb and illuminates it.



Alternating Current and Voltages.

DC or Direct Current always flows in one direction, DC comes from batteries and AC/DC convertors

AC or a.c is different from DC as it keeps changing direction. Basically anything that alternates is from a coil or generator that shifts phase, AC is easier to make and is also easier to manage voltage with.

Mains Electricity in the UK runs at 240V and cycles at a frequency (ƒ) of 50Hz meaning it cycles 50 times a second


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