'The Atoms Family' (A Great Electrical Resource Site)
'Just for Kids' (Fun and Games - About Electricity)
'Theatre of Electricity'
2.1. - Energy Forms and Transformations
Neon signs have applications of electrical technology.
- First, electricity must travel all the way through the tube in order for the gas to glow.
- Second, The sign has to have a control to turn it off and on.
- Third, the sign must be safe
A Unique Circuit
Neon gas acts in the same way as a wire. It conducts the flow of charged electrons from the negative terminal to the positive terminal. There are other gases which act as conductors, including:
- Neon - gives a orange-pink light
- Neon and argon - give a purple light
- Helium - gives a yellowish-white light
Neon is usually an insulator, but electricity 'excites the neon atoms, electrons themselves from the atoms, giving a mixture of charged particles uinside the tube (which are good conductors).
Conductors and Insulators
Electrons are bonded closely to the nuclei in insulators (allowing little movement), while in conductors, the electrons are free. When electricity is added, the electrons move toward the positive terminal.
Semiconductors are almost perfect conductors - they have almost no resistance to electron flow. The largest obstacle is to get the semiconductor to work at reasonable temperatures for practical applications.
Using Conductors, Resistors and Insulators
A special type of conductor, called a resistor allows electrons to flow, but provides some resistance.
Resistance is a measure of how difficult it is for the lectrons to flow through a conductor. It is measured in ohms. The more resistance a substance has, the greater the energy gain it receives from the electrons that pass through it. The energy gain is evident in leat and light energy (light bulb filament, wire in a toaster). Solutions can also be resistors. 'Lie detectors' are also special applications of resistance within the body (skin resistance, blood pressure and respiration). An increase in stress (usually associated with a lie) will improve conductivity and show a 'peak' in the recording device.
Switches and Variable Resistors
A switch is a device that allows the flow of electrons or stops the flow. When the switch is open, the is no flow, because there is a gap in the conductor. When the switch is closed, the switch becomes the 'gap replacement' and allows the flow of electrons to continue. To change the electron flow gradually, a variable resistor, or rheostat is used (a dimmer switch, volume control knob).
2.2. - Modelling and Measuring Electricity
A waterfall is used, as a model, to demonstrate voltage. Water flows when there is a change in the gravitational potential energy (elevation). Electricity will not flow unless there is a change in electrical potential (voltage).
Modelling Resistance and Current
Flow of water in pipes is used, as a model, to demonstrate resistance. The size of pipe determines the volume of water allowed through it. The amount of resistance, in a circuit, determines the size of the current.
Georg Simon Ohm, a mathematician, proved a link between voltage (V), current (I) and resistance (R). The unit of resistance was named after him, the ohm.
Ohm's Law states that as long as temperature stays the same:
- the resistance of a conductor stays constant, and
- the current is directly proportional to the voltage applied
Applying Ohm's Law
Sample textbook problems p. 306 and 307 (use R=V/I)
If the temperature of a resisitor changes, the resistance changes as well (resistance is usually low when the resisitor is cool, and as the temperature increases, so does resistance).
Using Test Meters
Voltmeters measure voltage difference (voltage drop). Ammeters measure current (rate of flow) in amperes.
Small currents are measured using galvanometers.
Multimeters can measure voltage, current and resistance in a circuit.
Types of Resistors
Different resistors are used for different applications, especially in electronics. There are many styles, sizes and shapes. The two most common are the wire-wound and carbon-composition types.
2.3. - Analyzing and Building Electrical Circuits
Engineers and designers of electrical circuits use symbols to identify components and connections. A drawing made with these symbols is called a schematic or schematic diagram.
Basic circuit symbols
All circuit diagrams have four basic parts:
- sources - provides energy and a supply of electrons for the circuit
- conductors - provides a path for the current
- switching mechanisms - controls the current flow, turning it off and on, or directing it to different parts of the circuit
- loads - converts electrical energy into another form of energy
Circuit Analysis Example - Bulldozer
The toy bulldozer has 2 loads, a motor and a bulb. 2 1.5V cells act as the energy source. A switching mechanism connects to 4 wires. The circuit diagram follows.
Parallel and Series Circuits
A series circuit provides only one path for the current to flow,
whereas, a parallel circuit provides multiple pathways.
Applications of Series and Parallel Circuits
House Wiring - uses parallel circuits
Microcircuits (Integrated Circuits) - transistors are used with three layers of specially treated silicon, with the middle layer (receiving a small voltage, allowing it to control the voltage in the outer layers, allowing them to act as switches. Microcircuits are made up of transistors and resistors and is buit on an extremely small scale.