Electronics

This week we have started to look at electronics.

An electrical circuit is a closed loop network of different components and a power supply.

The main properties of an electrical circuit are:

Current: the flow of electrons around a circuit.  It flows from positive to negative, or from a high point to a low point - like water.  Current is measured in Amps (A)

Voltage: the "push" - voltage drives the current around the circuit.  Voltage is measured in volts (V)

Resistance: a material's reluctance to allow current to flow.  All materials can conduct electricity, but they all have different resistance - those who let current flow easily - conductors - and those which make current flow difficult - insulators.  The more resistance a material has, the more voltage is required to make current flow.  Resistance is measured in Ohms (Ω) (Though sometimes people are lazy and write R instead of Ω)

First we looked at resistors as components.  Resistors are important to gain some control over the voltage and current in a circuit as some components are sensitive and too much current could destroy them.  The following picture explains how to read resistor colour code. 

This website can also be used to check, but in real life you may not have this luxury!

Remember your prefixes. You already use Kilo (k) and Milli (m) on a daily basis i.e. kg and mm.  So kilo is a thousand - 1000 or x103 and milli is a thousandth - 0.001 or x10-3.  To help you organise your numbers you may be able to find the engineering mode on your calculator which will put your number in the correct scientific notation to quickly convert to the correct prefix.  This table should help you make conversions.

The first type of circuit we looked at were series circuits - where component are connected end to end.  Be built a circuit with a resistor and an LED in series and measured the voltage over the resistor for different resistor values. 

To measure voltage we had to place one probe on one leg of the resistor and the other probe on the other leg.

We found that as the resistance increased, the voltage dropped over it increased.

We also found, through circuit simulation and using Kirchoff's law, that all the voltages dropped in the circuit must equal the supply voltage i.e. VR + VLED = VS

In this circuit the switch has no resistance as it is a very good conductor when closed.  You can see that the voltage over the resistor (4.1v) and the voltage over the LED (1.9V) equal the supply (6v)

We then used simulation software to measure the current in a series circuit.  The flow of current is the same throughout the loop and therefore current is the same at all points.  Also the larger the resistor, the less current can flow in the circuit.

The relationship between voltage, current and resistance is known as Ohm's law and can be described using the equation V = IR where V = voltage, I = Current and R = Resistance.

Other things that you should be aware of:


Types of Switch
Ohm's Law