CONDUCT BASIC RESEARCH AND EXPERIMENTS …...FSSSCN201 Conduct basic research and experiments into...

CONDUCT BASIC RESEARCH AND EXPERIMENTS INTO MATTER AND ELECTRICITY FSSSCN201

LEARNER GUIDE - ELECTRICITY

Learner Guide - Electricity FSSSCN201 Conduct basic research and experiments into matter and electricity Version 1.0 of 20

TABLE OF CONTENTS Contents TABLE OF CONTENTS ........................................................................................................ 2 Electricity ......................................................................................................................... 3

What is electricity? .................................................................................................................... 3

How electricity is made? ............................................................................................................ 4 Current electricity ..................................................................................................................... 5

Types of Batteries ...................................................................................................................... 9 Voltaic Pile ................................................................................................................................ 9

Wet (Electrochemical) Cell ..................................................................................................... 10

Dry (Electrochemical) Cell ....................................................................................................... 10

Lightning and Static Electricity ................................................................................................. 10

How do sparks form? .............................................................................................................. 10

Earthing .................................................................................................................................... 11

Lightning rods .......................................................................................................................... 11 Electrostatics............................................................................................................................ 11

Charged objects ...................................................................................................................... 12

Electricity and Electric Shock........................................................................................... 13 It should be remembered that even insulators will conduct electric current if the voltage is high enough. ............................................................................................................................ 14 Which is worse, high voltage or high current? ........................................................................ 14

What is a fatal current? ........................................................................................................... 15 Other factors in electric shock ................................................................................................. 15

Earth Wires .............................................................................................................................. 16 Fuses protect against electrocution ........................................................................................ 16

Different fuses and their Uses ................................................................................................. 17 Circuit breakers ........................................................................................................................ 17

Voltage ..................................................................................................................................... 17

The effects of different levels of current on the body ............................................................ 18 Treatment of victims of electrical shock ................................................................................. 19

Guidelines for prevention and control of electrical accidents ........................................... 20


ELECTRICITY Energy is the ability to do work. Energy comes in different forms:

⋅ Heat (thermal)

⋅ Light (radiant)

⋅ Motion (kinetic)

⋅ Electrical

⋅ Chemical

⋅ Nuclear energy

⋅ Gravitational

⋅ There are two types of energy:

⋅ Stored (potential) energy

⋅ Working (kinetic) energy

All of the changes that happen in the universe depend on energy. To cause a change to occur, energy may change form. For example, the chemical energy in wood changes to thermal energy (heat) when the wood is burned. However, though energy can be transformed, it cannot be created or destroyed. That is, the total amount of energy in a system never changes. This forms the basis of the law of conservation of energy,

What is electricity? Electricity is a form of energy. It is invisible and is created when particles become charged. Wide use of electrical energy is made in every aspect of our lives. It has great advantages over other forms of energy: it is easy to transport using wires and other conductors to where we want; it is easy to change into other forms of energy that we need like heat, light and sound; and it can be quite easily made from other energy forms, like kinetic, nuclear and heat. There are two different types of electricity that we will consider - static electricity and current electricity.


How electricity is made? Electricity for powering our homes is made in power stations. A power station contains large machines called turbines, which are turned very quickly. Power stations need large amounts of energy to turn the turbines. Most use heat energy produced from burning coal. Others use wind energy or moving water. The spinning turbine causes large magnets to turn within wire coils - these are the generators. The moving magnets within the coil of wire causes the electrons (charged particles) to move within the coil of wire. This is electricity. In Australia, due to our access and abundance of coal, a majority of our electricity is sourced forma a coal fired power station. There are many other ways to generate electricity.

Electricity generation across Australia

Image source : https://www.originenergy.com.au/blog/about-energy/energy-in-australia.html

An overview of the steps in a coal-powered station: ⋅ The large chunks of coal are first crushed into a fine powder. This is called

pulverisation.


⋅ The coal is then transported to a furnace where it is burnt.

⋅ The thermal energy from the burning coal is used to boil water and generate steam.

⋅ The steam pushes the blades of the turbine and so the turbine spins.

⋅ The turbine is connected to the shaft of the generator which then rotates large magnets within wire coils, which generates electricity.

⋅ The electric current is sent through the power lines to businesses and homes.

Source: http://www.mstworkbooks.co.za/natural-sciences/gr9/gr9-ec-06.html

There are two types of electrical currents that can flow through wires: direct current (DC) and alternating current (AC).

Current electricity An electric current is moving electric charge. This moving electric charge, oe electricity, is a flow of electrons direct current and alternating current

Electricity flows in two ways: either in an alternating current (AC) or in a direct current (DC). Electricity or "current" is nothing but the movement of electrons through a conductor, like a wire. The difference between AC and DC lies in the direction in which the electrons flow. In DC, the electrons flow steadily in a single direction, or "forward." In AC, electrons keep switching directions, sometimes going "forward" and then going "backward." Alternating current is the best way to transmit electricity over large distances.

http://www.mstworkbooks.co.za/natural-sciences/gr9/gr9-ec-06.html

http://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjbxZXAuOzUAhVCbrwKHUpVAewQjRwIBw&url=http://www.mstworkbooks.co.za/natural-sciences/gr9/gr9-ec-06.html&psig=AFQjCNH9WE7ddxLzjqg1ZB3pM5vKz5KdMw&ust=1499148196330124


Comparison chart: Alternating Current versus Direct Current comparison chart

Alternating Current Direct Current

Amount of energy that can be carried

Safe to transfer over longer city distances and can provide more power.

Voltage of DC cannot travel very far until it begins to lose energy.

Cause of the direction of flow of electrons

Rotating magnet along the wire. Steady magnetism along the wire.

Frequency The frequency of alternating current is 50Hz or 60Hz depending upon the country.

The frequency of direct current is zero.

Direction It reverses its direction while flowing in a circuit.

It flows in one direction in the circuit.

Current It is the current of magnitude varying with time

It is the current of constant magnitude.

Flow of Electrons Electrons keep switching directions - forward and backward.

Electrons move steadily in one direction or 'forward'.

Obtained from A.C Generator and mains. Cell or Battery.

http://www.diffen.com/difference/Alternating_Current_vs_Direct_Current

.

Some materials hold their electrons very tightly. Electrons do not move through them very well.

These things are called insulators. They allow very little current to flow. Plastic, cloth, glass and dry air are good insulators. Wires carrying electricity are covered in plastic to prevent electric

shocks.

Other materials have loosely held electrons which move through them very easily. These are called conductors. They allow large electric currents to flow. Most metals are good conductors.


Resistance is the property of a substance that prevents the flow of electrons, and it can be measured. Since insulators do not allow electricity to pass through them easily, they have high resistance. Materials with low resistance are conductors because they let electricity flow through them easily. Electricity passing through a material will heat the material relative to the resistance of that material. This is important to us because heat and sometimes light is produced when electrons meet resistance. In a simple torch, for example, the filament of fine tungsten wire inside the bulb has great resistance and becomes so hot that it gives off a brilliant white light. In the same basic way, irons and toasters create heat by using resistance.

Common household electrical appliances can be grouped according to the main purpose for which the electrical energy is used.

They may be devices which use electricity to produce light such as light globes and torches or heat such as kettles and dryers. Audio-visual devices convert electricity to sound, a visual image or both and include radios, televisions and computers. Mechanical devices usually contain motors and include drills, fans, video and CD players. Two things are needed for electricity to move:

• a power source to provide the electrical energy such as a battery or generator • a pathway through a conductor.

Electrons from the power supply flow along a conducting path and back to the power supply making an electric circuit. A bulb or an electric device can be a part of the pathway and changes the electrical energy into some other form of energy which we can use such as light energy. Electric current is the flow of electrons (electric charge) through the circuit and is measured in amps. Voltage is the electrical pressure that causes the current to flow through the circuit and is measured in volts.


An electric circuit It is not usual to draw an electric circuit like the diagram above. Symbols are used instead.

Circuit symbols Maps of electric circuits include symbols such as these and are called circuit diagrams. If there is a break in the flow of electric charge, the circuit is said to be open. In a closed circuit electricity flows completely around the loop.

An open circuit and a closed circuit Circuits can be made in different shapes. They can be in 'series' or in 'parallel'. A series circuit occurs when the electricity leaves the power supply (battery), travels along the pathway (wire), through the bulb (load) and back to the power supply. A series circuit can contain several lights but has only one continuous pathway. An example of this kind of circuit is found in Christmas tree lights where the entire string of lights goes out if one bulb is missing or not functioning.

insulator

conductor


In a parallel circuit, each bulb would have its own pathway to the power supply so that it forms its own circuit. In a parallel circuit, Christmas tree lights would not go out if one light in the strand were missing or not functioning.

Types of Batteries

Voltaic Pile The simplest battery is the voltaic pile, named after a scientist called Alessandra Volta, who first developed it in 1800. His simple battery (shown below) was a stack of layers of zinc, blotting paper soaked in salt water, and silver. When you attach a wire to the top and bottom of the pile you can measure the voltage produced by the pile.


Wet (Electrochemical) Cell An electrochemical cell is a battery similar to the voltaic pile but with the following differences:

• only one zinc plate • the silver layers are replaced with one copper plate • instead of the blotter with salt water there is a container of dilute copper sulfate

solution • the copper and zinc plates are called the electrodes and the copper sulfate is the

electrolyte. The copper plate is the positive electrode while the zinc plate is the negative electrode. A chemical reaction occurs and produces electrons. When the electrodes are connected by a wire electrons flow through the wire and so an electric current is produced. The electrolyte conducts electric charge through the liquid solution. Because the electrolyte is a liquid, an electrochemical cell is sometimes called a wet cell.

Dry (Electrochemical) Cell In this type of battery the carbon rod is the positive electrode. The electrolyte is a “dry” paste of ammonium chloride, and so this type of battery is also known as a dry cell. The negative electrode is the zinc case.

Lightning and Static Electricity When you take off your woollen hat, it rubs against your hair. Electrons move from your hair to the hat. So now your hair has lost electrons (leaving each hair with a positive charge) and the hat has gained electrons (giving the hat a negative charge). All those positively charges will repel each other, so the hairs try to get as far from each other as possible. The fa1ihest they can get is by standing up and away from the others. Bad hair day! How do sparks form? Sparks are the result of charges jumping from one object to another. They occur either between two oppositely charged objects, or between an uncharged object and a charged one. If you've been walking around on nylon carpet on a windy day, you may have collected plenty of extra electrons. They are keen to get back off you and back to the ground - so the next time you touch a metal door knob - those electrons will jump back from you to the earth. You feel it as a zap, but you've just lost your collection of negative charges, and become neutral again.

http://en.wikipedia.org/wiki/File:Batteries.jpg


Now that you understand that objects gain and lose electrons and then become charged, you're ready to investigate the question: what causes lightning? Rain clouds are made up of tiny drops of water. Many of these drops have a small electric charge caused by collisions with other heavier particles within the cloud. During the collisions, the heavier particles gain a negative charge and the lighter particles gain a positive charge. The heavier negatively charged particles fall to the bottom of the cloud and the positively charged lighter particles rise to the top of the cloud (see Figure 3). These charges can then jump to other objects, such as the earth, to other clouds or even within the one cloud. The flash we see in the sky, when lightning strikes, is really a huge electric spark. As a cloud moves over the ground, the negative charges in the bottom of the cloud repel negative charges on the ground. So the ground near the bottom of the cloud has a temporary positive charge.

• Cloud-to-ground lightning occurs when negative charges from the bottom of the cloud move downwards towards the earth.

• Intracloud lightning occurs between opposite charges within one cloud. • Cloud-to-cloud lightning occurs between opposite charges on different clouds.

Earthing When a charged object is brought near the ground (earth) or actually touches it, the object can discharge (give out its electron charge) often with a spark. If you touch a charged object it can give you an electric shock when it discharges through your body to the ground (earth). The act of connecting an object to something that can conduct electricity to the ground is called earthing. Most electrical appliances have three-pin plugs. The bottom pin is called the earth because it's connected to the ground (earth) under or around your home. If there is a fault in an electrical appliance, the charge will flow to earth instead of through your body.

Lightning rods Lightning rods are another example of earthing. They are metal rods designed to protect buildings from damage or destruction caused by lightning. When the rod is struck by lightning, it causes the charges to flow to the ground (earth). Lightning rods usually have a top part of copper above the roof and a wire or iron bar which leads to the ground. The lower end must reach into the soil for the lightning rod to work.

Electrostatics You have experienced electricity if you have heard crackling as you comb your hair, have felt a shock after opening a car door and stepped onto the ground or have seen sparks when removing a nylon shirt in the dark. This is caused by a build-up of electric charge when electrons move from one object to another. The build-up of electric charge on an object is called static electricity. Static electricity is electricity at rest on an object; it does not flow through the object.


Charged objects How can you move electrons from one place to another? One very common way is to rub two objects together. When two different materials are rubbed together, the electrons of one material can easily jump onto the other. When this happens one material becomes negatively charged, while the other becomes positively charged. Positive and negative charges behave in interesting ways. Two things with opposite charges (a positive and a negative) will attract or pull towards each other. Two things with the same charge (two positives or two negatives) will repel or push away from each other. A charged object will also attract something that is neutral.

Like charges repel, unlike charges attract Water vapour in the air helps move electrons away from charged objects. The air is moister in winter so static electricity does not build up as much as in the summertime when the air is very dry.

+ + - +


ELECTRICITY AND ELECTRIC SHOCK The very nature of electricity can make using and working with it hazardous. A hazard is a situation with the potential to harm life, health or property. Before a hazard can be controlled we must first be aware that it exists. Carefully look at the photograph below which shows an untidy bundle of electrical wiring.

https://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiS47ynwLXUAhXCJJQKHbmWB1EQjRwIBw&url=https://www.dreamstime.com/stock-photo-overloaded-power-board-surge-protector-image61833378&psig=AFQjCNGNpCxLHSOlm6G_x2mvXbAV0Qix-g&ust=1497260473518816


The world around us consists of substances we can see, smell, taste and feel. All of these substances are made up of atoms, a combination of protons, neutrons, and electrons. If an external supply of electrons are forced into a substance, the electrons that are already in the substance can be forced to move through it. In electrical terms:

• Voltage is the electrical pressure caused by the external supply of electrons • Current is the actual movement of electrons through the substance

Another term, the Resistance of a substance, relates to how easily electrons can pass through the substance. Some materials have a low resistance and are called conductors of electricity. Examples include copper, aluminium, and steel. Other materials have a relatively high resistance to current flow and are called electrical insulators. Some common insulating materials include plastic, rubber and dry timber.

It should be remembered that even insulators will conduct electric current if the voltage is high enough.

Which is worse, high voltage or high current? You may think that 1000 V would be more deadly than 100 V, but this is not necessarily true. The normal household current of 240 V is responsible for most deaths associated with electrical shock. Deaths have occurred with DC shocks of only 42 V. Remember, the real measure of the intensity of an electrical shock lies in the amount of current to which the body is exposed. You may all remember playing with a Van de Graaff generator at school (that big silver ball with an oversized elastic band inside which makes your hair stand on end when you touch it). This device operates at 10 000 V, but the current associated with this is minimal, so it can be used for party tricks safely. This is because the high voltage is associated with high resistance. In general however, most high voltage devices must be treated as very dangerous because if they find a path of low resistance to return to their source (such as through your body) a very large current will flow, generally resulting in electrocution.


The combination of high voltage and high current is extremely dangerous. Devices in this category should only be handled by those who are properly trained.

What is a fatal current?

The lowest current which can be felt by the average person is between 0.8 to 1.2 mA. (milliamps). This is referred to as the threshold of sensation and is unlikely to cause any damage to body tissue. A current of around 2-10 mA will cause a person to pull away from an object This is associated with most fall injuries. The brain sends messages to the muscles via low current electrical impulses. Current in the range 10 to 100 mA will override these signals. In this situation, you cannot let go of the source of the current as the brain can no longer communicate with the muscles, which instead respond to the external electrical stimulus. For this reason it is suggested that you test electrical apparatus with the back of your hand before operation. This prevents a grip response from your hand which then can't let go of the device. Exposure to currents between 100 and 200 mA generally causes death. This is because the heart goes into ventricular fibrillation, where it ceases to pump and goes into a qu1vering motion. This condition can only normally be reversed by a special device known as a defibrillator. Electrical shocks with current flows of greater than 200 mA lead to symptoms similar, but far more exaggerated than those received in the current range from 10-100 mA. Surprisingly, a person is much more likely to survive a shock of 500 mA than 150 mA. This is because the heart is likely to clamp shut under higher current and hence does not go into fibrillation. The table on the page 23 (The effects of different levels of current on the body) shows the effect of different levels of current on the body. Note that voltage is not a consideration. Effects vary with AC or DC currents and from person to person so these must be treated as approximate only.

Other factors in electric shock The path that the current takes through the body also determines the amount of damage sustained by a victim of electric shock. This is because the electrical current may travel through vital organs in the body causing them to be damaged. If this damage is bad enough the organs will cease to function and life will be threatened. Predicting the internal damage caused by electric sho9k is not easy, but it is very likely that the respiratory control centre in the brain will be affected and breathing will stop. If this· occurs, brain damage due to lack of oxygen will occur within 2-4 minutes. The victim is also likely to sustain muscular paralysis and extreme pain (due to the burning effect of the current). If cardiopulmonary resuscitation (CPR) is applied within two minutes after the shock occurs, the victim’s chances of recovery are much greater.


Earth Wires In Australian homes, most electrical wiring has three separate “cores”. Each core is connected to a pin in the plug of the appliance and is coated with plastic insulator of a different colour. The brown wire is active and takes current to an appliance. The blue wire is neutral and simply completes the circuit. The green and yellow wire is the earth wire, and takes current away from the appliance if there is a problem.

http://www.teachers.ash.org.au/jfuller/safety/safety1.htm

The earth wire is connected to a metal stake that has been driven into the earth outside the house. The earth wire in this photo at right is attached to the water pipe and to a spike in the ground. It will carry electricity to the ground outside the house if there is a problem, such as a short circuit.


Fuses protect against electrocution When a current flows through a resistor it generates heat as it tries to pass. A real life example of this is a fuse. A fuse is often a thin piece of wire. If too much current is flowing through the fuse it gets too hot and it melts. This stops the current from flowing and helps to prevent electrocution and electrical fires, caused by sparks and overheating of electrical appliances. Circuit breakers are special switches that turn off the current if too much is flowing through a circuit. Fuses (or circuit breakers) are used in all household circuits. There are different fuses for different circuits, the thicker the fuse wire, the more current it can take.

The plug shows the three “cores” each attached to a separate “pin”




Different fuses and their Uses

Size of fuse wire, Amps (A) Circuits it’s used in

8 A Lights

8 A Hot water system

15 A Power points

30 A stove

Circuit breakers Circuit breakers switch the power off if too many appliances are being used, again minimizing an electrical accident.

http://en.wikipedia.org/wiki/File:Jtecul.jpg

Voltage While it's the current that causes the major injury from electric shock, it's the voltage that actually drives the current through the body. The higher the voltage, the more pressure there is to push electrons through the body. Standard voltage classifications in Australia are:

• Extra-Low Voltage (ELV) - up to 50V a.c. or 120V d.c. • Low Voltage (LV) - greater than ELV and up to 1000V a.c. or 1500V d.c. • High Voltage (HV) - greater than 1000V a.c. or 1500V d.c.

Generally speaking, the higher the voltage, the greater the risk of electric shock. That's not to say however that ELV isn't dangerous! Under certain conditions (e.g. a damp environment), ELV also has the capacity to injure, or even kill. For example, a 120V battery can have the capacity to deliver several hundred amps if the terminals were short circuited, resulting in horrific flash burns for anyone standing too close.

http://upload.wikimedia.org/wikipedia/commons/f/fd/Jtecul.jpg

http://en.wikipedia.org/wiki/File:Jtecul.jpg


The effects of different levels of current on the body

Approximate current level (mA)

Effect on body

0.8 – 1.2 Threshold of sensation. Little or no damage is sustained.

2 – 10 Pain and response to pull away from object. The cause of many falls.

10 – 100 Causes muscles to clamp. May lead to hands gripping conductor with the victim unable to let go. Pain and burn damage increases with current.

100 – 200 Generally causes death by sending the heart into ventricular fibrillation. Victim does not generally respond to first aid.

Above 200 Leads to muscular paralysis, extreme burns and pain. Does not necessarily cause death as victim may respond to first aid, but higher current levels will generally kill victim without swift action from rescuers.

Current flow through vital organs Electrical current will take the path of least resistance through your body. It is difficult to estimate the resistance between different parts of your body as this varies greatly according to health and environmental conditions. Hence it is difficult to predict the exact path that a shock has taken. Often internal organs may be damaged while the victim outwardly appears to be in perfect physical order.


Treatment of victims of electrical shock Too often a person trying to render assistance to an electrocution victim is also electrocuted. Do not touch a person who is in contact with a live power source, as this will lead to you also becoming part of the circuit and being similarly affected. The best approach is to turn off the power if this is possible, but don't waste time looking for the power switch if it is not accessible as it is important to remove the victim from the source of current as soon as possible. Try to dislodge them from the source of power without endangering your own safety. A dry length of wood can often be used to 'prod' a victim and remove them from the live power source. Insulate yourself from earth so that a current will not flow through your body (remember the old rubber soles!). Also insulate yourself from the power and the victim before attempting to remove them from the source of electrocution. Rubber gloves or leather materials are good insulators, alternatively dry timber or clothing may be used. If there is no other alternative, striking the victim with a swift blow from the hands or feet may be considered as a last resort, but if this is necessary avoid direct contact with the skin. After successfully removing a person from a live lower source, resuscitation can be commenced if they have stopped breathing or medical treatment may be given if they are conscious.

Because of the possibility of internal organ damage it is advisable to refer all victims of electrical shock for

medical treatment.


GUIDELINES FOR PREVENTION AND CONTROL OF ELECTRICAL ACCIDENTS Common sense and care and a few basic techniques will greatly decrease the likelihood of you being involved in an electrical accident. The points which follow list appropriate actions to minimise the likelihood of an electrical accident in your workplace.

• Do not use instruments with frayed or damaged power cords, and do not overload power points.

• Report all defects or accidents with electrical equipment. • A licenced electrician must be used to work on ANY electrical device. • Touch all electrical equipment with the back of your hand before use. This will prevent

you accidentally gripping the device if it is live. • Install circuit breakers on all power supplies. • Apply danger tags (also known as safety tags) or locks where required. These are used

to prevent the operation of faulty equipment. If you find a piece of equipment which is faulty or unsafe, you should switch it off and tie a danger tag to the isolation switch. If the equipment is equipped with lock-out isolation it should be used in addition to the safety tag. This prevents operation until the problem is fixed. Only the person who fitted a danger tag is allowed to remove it. Never use any piece of equipment fitted with a danger tag. If you are required to isolate the component from other electrical devices to render it inoperative, then you should also attach a danger tag to the main power switch or circuit breaker.

• Install earth leakage core balance current breakers (also known as safety switches) where possible. These monitor the current into, and out of a circuit, and when they are not equal (such as when a person is providing an alternate route for return of electrons to the power station through their bodies, i.e. they are being electrocuted) they switch the power off.

• Do not attempt -repairs on equipment with which you are not licenced to, familiar with or have no expertise.

• Wear insulated footwear (or work on insulated flooring or mats). This prevents you from providing a path for electron flow to earth through your feet.

• Ensure all power points are off when plugging in or disconnecting devices. • Do not store flammable substances near control panels, fuse boxes or electrical

equipment which may cause a spark. • Avoid wearing jewellery or large belt buckles when operating electrical devices, as

these are excellent conductors. • Try to avoid using extension cords, but if you must use them ensure that they are fully

unwound to prevent overheating. • Remember water and electricity do not mix. Electrical appliances should not be used

with wet hands or feet. • Electrical current always takes the path of least resistance. Do not allow your body to

become part of this path.

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