Presentation on theme: "LCA 1 Session 2. Electric Current is produced when electrons move through a material. Metals have free electrons so that is why electricity can travel."— Presentation transcript:
LCA 1 Session 2
Electric Current is produced when electrons move through a material. Metals have free electrons so that is why electricity can travel through metals. Materials that allow electricity to flow through them are called “ Conductors”
Current flows from + to – Materials that Do Not allow current to flow through them are called “Insulators” Plastic, wood and rubber are insulators.
A power source is needed to push the electrons around the circuit. This pressure is called electromotive force or e.m.f. It is measured in Volts (V) It is like a pump pushing water, the Voltage pushes current.
A Battery is made up of cells. Each cells gives 1.5V So if a Battery has 4 cells that means 4 X 1.5=6V Battery The current from a Battery flows in one direction and is called Direct Current (DC)
In Ireland there is “Electric Ireland” (ESB), “Bord Gais” and “Airtricity” These companies supply Alternating Current (AC). The flow changes direction 50 times every second. + to – then – to +. They supply 220V
Every circuit has to have voltage, current and resistance. Resistance is what tries to stop current flow. Some conductors are made to have some resistance and these are called resistors.
NameUnitSymbolOhm’s Law VoltageVoltsVV CurrentAmpsAI ResistanceOhm Ω R
This is how voltage, current & resistance are linked. VoltageV = I x R Current I = V/R ResistanceR = V/I
Colour CodesA 3-Pin Plug Brown = Live Blue = Neutral Yellow/Green = Earth Pg 186 Fig 14.14
Live Wire is BrownNeutral Wire is Blue The function of the Brown wire which is called the Live is to bring the current from the power station to the appliance that you are using. The function of the Blue wire which is called the Neutral is to return the current to the power station from the appliance that you are using.
The Earth Wire The metal body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary
Earth Rod If for whatever reason there is a fault, all the metal parts of the electrical appliance may carry current which means there is the danger of electric shock. The earth takes the current to ground and makes the appliance safe
How Circuit Breakers Work: Circuit Breaker: At Work in Your Home How Circuit Breakers Work:Circuit Breaker: At Work in Your Home The circuit breaker is an absolutely essential device in the modern world, and one of the most important safety mechanisms in your home. Whenever electrical wiring in a building has too much current flowing through it, these simple machines cut the power until somebody can fix the problem. Without circuit breakers (or the alternative, fuses), household electricity would be impractical because of the potential for fires and other mayhem resulting from simple wiring problems and equipment failures fuses
In a parallel circuit each bulb gets a + and a -. Therefore as seen in the diagram the power supply is a 9V battery, this means each bulb gets 9V and if one blows the others will light.
It a series circuit each bulb is wired after the previous one. As the diagrams show the Voltage is 120V so each bulb gets 60V. If one bulb blows it will break the circuit.
Potential Divider The potential divider forms the basis of many electronic circuits and allows us to use a variety of Sensors such as LDRs (light), thermistors (heat) and moisture probes etc. The process can be thought of as three distinctive parts or blocks. Let us take as an example a situation whereby an Alarm sounds if an LDR is placed in dark conditions. The problem could be considered as shown below.
The alarm is an LED but it could be any output device.
LED Note: we will look at how the transistor works later.
With this device we can create a potential difference Because it has 3 legs and it’s resistance can be changed manually.
A Transistor is a an electronic switch It has 3 legs Collector, base & emitter Current will only flow through it if there is 0.7V at the base. So it is turned on and off electronically.
V is above 0.7 = LightsV is below 0.7 = unlit 0.4V
Resistor- Slows down the flow of current Transistor- Is an electronic Switch
1 Resistor 2 Buzzer Light Dependant Resistor- Resistance changes with changes in light.
1.LED 2.Transistor 3.Switch 4.Buzzer
C Switch D Resistor 9V is the power of the battery, Voltage is the force it’s pushing the current around the circuit with.
A = 2 B= 1 A=LED –Indicator B=Transistor-Switch
1.=Variable Resistor 2.=Resistor 3.=Transistor 4.=Bulb Thermister – resistance changes with changes in heat.