Electricity & Electronics

LCA 1Session 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”

Electric Current

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.

Power Sources

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)

A Battery

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

Electricity Supply Company

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.

Voltage, Current & Resistance

Name Unit Symbol Ohm’s LawVoltage Volts V VCurrent Amps A IResistance Ohm Ω R

Measurement

This is how voltage, current & resistance are linked.

Voltage V = I x R

Current I = V/R

Resistance R = V/I

Ohms Law

Wiring a Plug

Colour Codes A 3-Pin Plug

Brown = Live

Blue = Neutral

Yellow/Green = Earth

Pg 186 Fig 14.14

Functions of the wires.

Live Wire is Brown Neutral 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

Safety

Safety

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

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

Circuit Breaker

Parallel Circuits 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.

Series Circuit 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.

Variable Resistor

The alarm is an LED but it could be any output device.

LED

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.

Variable Resistor

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.

Transistor

Transistor

V is above 0.7 = Lights V is below 0.7 = unlit

0.4V

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Resistor- Slows down the flow of current

Transistor- Is an electronic Switch

2009

1 Resistor

2 Buzzer

Light Dependant Resistor- Resistance changes with changes in light.

20081. LED

2. Transistor

3. Switch

4. Buzzer

2006

2007

C SwitchD Resistor

9V is the power of the battery, Voltage is the force it’s pushing the current around the circuit with.

2006

A = 2B= 1

A=LED –IndicatorB=Transistor-Switch

2005

1.=Variable Resistor2.=Resistor3.=Transistor4.=Bulb

Thermister – resistance changes with changes in heat.

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