E_Concept_1
What is Electricity
What is Electricity
In order to begin to understand what electricity is, it is necessary to know some things about the make-up of physical substances, or matter. Matter is made up of small particles, or atoms.A useful model of an atom is a central nucleus containing positively charged particles, surrounded by a 'cloud' of negatively charged particles, or electrons. Normally, in any one atom, the positive and negative charges will balance; but sometimes they can become unbalanced, leading to a build-up and flow of electrons that we call electricity.
Some insulators (materials that do not readily allow electricity to flow through them) can build up what is termed a 'static' charge through friction.The effect of rubbing an inflated balloon against hair is a good example. Extra electrons are collected by the balloon, giving it an overall negative charge.The attraction of opposite charges allows it to 'stick' to a non-conducting, positively or neutrally charged surface such as a wall or ceiling, or to attract fine hair and make it stand on end.
Sometimes, when the charge difference built up is very large, it may balance out by causing all of the electrons to be discharged very quickly.As you get out of a car or walk across a carpet, you may receive a 'shock' — a rapid discharge of electrons. Because of the movement of water droplets within thunder clouds, huge charges can build up inside them. When these discharge against oppositely charged parts of the cloud or against the ground, the energy of the charge literally blasts the air apart in creating a path for the discharge. When this happens, the explosion can be seen as a flash of light and heard as thunder. A spark from a gas cooker ignition system has the same effect, though on a much smaller scale.
The electrical flow associated with battery and mains electrical equipment is very different from a static charge. Electricity of this kind flows through conductors (materials that allow electricity to flow through them), which are usually metals. Metals have a particular structure that means the electrons are not securely attached to any one atom, allowing them to 'wander' from atom to atom in a random way; they can thus become part of an electrical current. This form of electrical flow is very different from the electromagnetic radiation of light or radio waves.
In a relatively thick piece of a good conducting material, such as a cable, the resistance to the flow of electrons is minimal over the distance the electricity is flowing.The thinner or poorer the conductor, the more the flow is restricted. As the electrons attempt to flow through the material, the resistance to their flow causes a kind of friction that makes the material heat up.
Sometimes a resistor will heat up so much that it begins to glow
Resistance can be useful! Electrical resistance is used to generate heat and light in filament light bulbs, electric kettles, electric fires and hairdryers.The special part of these devices which resists the flow of electricity and heats up is called the 'element'.
Electricity is generated from a number of primary energy sources, all of which produce movement that operates a dynamo. In a dynamo, a coil of wire is turned within a strong magnetic field; this causes an alternating current to be induced in the coil, and so electricity is produced. Most
generation systems burn fuel (oil, coal and gas) or use a nuclear reaction to heat water:
the steam is used to turn turbines that drive the dynamos. Hydroelectric power, windmills, tidal and wave generators use movement to turn the turbines directly, and are therefore more environmentally friendly.
Electricity is distributed around the country, from power stations to consumers, by the National Grid.This is a network of 'power lines' which operate at charge differences (voltages) of up to 40,000 volts. As domestic systems in this country only use 220—240 volts, the voltage has to be 'stepped down' in transformers for local supplies. By transporting electricity around the country at very high voltages, there is less energy loss due to electrical resistance.
Batteries contain chemicals which 'store' electrical charge. When connected into a complete circuit with a conducting material, the battery causes all of the wandering electrons in that material to move in a particular direction.This effect is known as direct current (DC). One way of imagining a battery is as a box with a compressed spring in it (when it is fully 'charged').When the battery is connected into a complete circuit, the spring slowly releases its energy to push the electrons around the circuit. When it is completely decompressed, it will have used all of •its stored energy and the battery will be 'flat' or 'dead'. With rechargeable batteries, visualise the spring being recompressed, so that energy can be released once more.You could also visualise recharging a battery as compressing air by blowing into a balloon — once the balloon is fully inflated (or 'charged') it is a store of (potential) energy.
Because of the way it is generated (see page 1 3), mains electricity supplies an alternating current (AC).The direction of the current changes back and forth very rapidly (in the UK, 50 times a second).This means that the electrons are made to go first in one direction and then in the opposite direction.This is like the difference between a handsaw (which goes backwards and forwards) and a chainsaw (which always goes in the same direction). DC is neither more nor less powerful than AC.
Strictly speaking, children at KS I and KS2 need only to consider the effects of electricity without being too concerned about its nature. Given the difficult concepts involved in theories about the nature of matter, this approach is sensible and makes the subject more accessible to children. However, it is important that teachers have some appreciation of the nature of electricity, so that they are able to understand the progress the children will be expected to make later on. If the children gain a secure foundation through an understanding of the applications of electricity in their primary science work, they will readily make the later transition to higher levels of understanding.
Battery — a case containing chemicals that react to cause a flow of electrons when connected into a complete circuit
Conductor — a material that allows the free flow of electricity through it (that is, the free movement of electrons between atoms).
Resistor — a device that restricts the flow of electricity in a completed circuit. Some resistors, such as a bulb or a motor, use the 'friction' of the restricted flow to produce light, heat or movement.
o The electric eel of South America can generate an electric charge of up to 650 volts — enough to stun a horse as it wades through a river.
o Lightning flashes can be up to 32km long and 3 metres in diameter. In Britain, there is an average of around 3.5 strikes per square km per year.
Note that much of the teaching of electricity at KS I and KS2 has to do with the practical issues of making circuits, using electrical devices and observing the effects.There is no need to focus on the children's understanding of the nature of electricity; but an overly nälVe interpretation of electrical effects can lead to misconceptions which will cause problems later on.
Electricity comes from shops.
Well, batteries do — and you can buy meter cards in shops. However, children should not think that mains electricity is carried home in a bag with the groceries. Ask questions such as: How could it get from the shop to the socket? What do we need to do to a hairdryer to make it work? Establish that mains electricity comes to our homes in cables, and explain about sockets and plugs.
What is electricity?
This one is the biggy!You need to judge what the child is capable of handling, and what you are able to explain. At this level, the emphasis should be on the effects of electricity, so try to explain it in term of what it does: It's what makes a bulb light up. If you are really pushed by a more able Year 6 child, it is better to admit uncertainty and direct him or her towards a textbook than to attempt to give an insecure explanation.To understand the 'flow of electrons' idea, children will need to some understanding of the nature and structure of matter and how this relates to electrical conduction,This will, no doubt, result in more questions than answers — which is the way that all good science develops. Take comfort in the fact that very few people could say with confidence that they really understand electricity.The key thing for you to ensure is that the children get to the next step without carrying too many misconceptions with them.
Conductivity (testing and sorting)
With KS I (or younger) children, construct a simple circuit with a battery, a bulb and a break in it. The children can then sort a given range of materials into ones that allow the bulb to light when they are used to fill the break in the circuit, and ones that don't.This can be extended by asking the children to test other things from around the classroom, Make it very clear that they must not touch anything that has to do with mains electricity (either the sockets or the equipment).