Key Stage 3

INTRODUCTION

Quantum Theatre for Science is Britain’s foremost Theatre-in-Education Company touring plays on the National Curriculum for Science to both Primary and Secondary schools nationally.

Founded 16 years ago in response to a lack of provision of drama in the science sector Quantum now has plays covering all aspects of the science curriculum, all written and performed in its own particular style, providing a highly original and entertaining teaching tool for the introduction and revision of the topics listed in the National Curriculum for Science.

This play, Everything you never wanted to know about electricity (and wished you hadn't asked...),aims to introduce and explain the sections on electricity for Key Stage 3 children, from basic atomic structure and electron flow, through constructing a circuit and circuit diagrams to electrical components such as resistors and transistors. We also introduce the main protagonists in the story of electricity and explain their part in it.

The material is presented in a Cabaret style, with various songs, sketches and vignettes illustrating the scientific concepts explored as we follow the fortunes of the two presenters who battle through interruptions, obstacles and real life drama in their attempts to present Everything you never knew about electricity (and wished you hadn't asked...)

A BRIEF HISTORY OF ELECTRICITY

We present a brief history of electricity and meet the following characters:

THALES (623-545 BC): one of the seven wise men of ancient Greek philosophy, Thales introduced geometry to measure the heights of pyramids and ship-to-shore distances. Although he was primarily a mathematician and astronomer he noticed that when a piece of amber was charged by friction dust and pieces of parchment were attracted to it and we now know this to be the first recorded observation of static electricity.

BENJAMIN FRANKLIN (1706-1790): Born in Philadelphia, Franklin built a very successful printing business and became famous through his writing. His interest in science stemmed from the printing of several scientific journals and lead him to conduct a dangerous experiment, flying a kite in a thunder storm. As it flew into the highly charged thunderclouds Franklin noticed tiny static sparks jumping from a metal key, attached to the bottom of the string, to his knuckles and he concluded that lightening was really one huge static spark. He later went on to invent the lightning conductor and was the first to use the terms ‘positive’ and ‘negative’ when describing electrical charge.

ALESSANDRO VOLTA (1745-1827): Volta was professor of physics in the Italian town of Como and in 1800 discovered how to make a battery, then called a Voltic pile. This was a major breakthrough, as all work on electricity to this point had had to use static electricity from static generators which proved difficult to control and depended on the dryness of the atmosphere. Now with Volta’s Pile electricity could be controlled and his contribution became immortalised in the name given to the unit of measurement for electrical supply: the Volt.

MICHAEL FARADAY (1791-1867): Faraday was born in Newington, Surrey (now the Elephant and Castle in South London) the son of a blacksmith. Although he only had a basic education he became interested in science when working in a bookshop at the age of 12. At 21, after attending a lecture given by the great Humphrey Davy, he was so inspired he sent Davy a hand written copy of his lecture notes and was taken on as Davy’s personal assistant. He is best known for his work on the generation of electricity using a magnet and a coil of wire and for his invention of the electric motor. Eventually Faraday became head of the Royal Institution and founded the Christmas Lectures for children in 1826 which still take place today.

Children can generate electricity for themselves using several metres of fine insulated wire, a magnet and a sensitive ammeter. Wrap about fifty or so turns of wire around a cardboard tube and connect the bare ends to the meter. Push the magnet into the tube and notice the needle kick as a small pulse of electricity is generated. Notice how the needle kicks in the other direction as the magnet is pulled out. Repeat the experiment with a stronger magnet and see how it affects the size of the current. Add more turns of wire to the tube and again see how this affects the size of the current. Notice how important it is that the magnet moves. Hold the magnet still and see if any current is generated.

ATOMIC STRUCTURE

We introduce atoms as being the basic building bricks of all materials (although we do not refer to specific elements to avoid confusion).

The nucleus of an atom is made up of the positively charged protons and the neutral neutrons. Electrons, with their negative charge, circle the nucleus thus:

Similar charges repel whilst opposite charges attract, thus the protons and the electrons are attracted to each other, holding the atom together.

Experiments can be set up to explore static electricity and the electrical charges in an atom using friction. Choose and insulator such as plastic, glass or resin and rub with a dry cloth. The friction between the insulator and the cloth causes the insulator to gain one type of charge and the cloth to gain the other type of charge as the insulator either loses its electrons or gains electrons from the cloth. Repeat Thales experience by seeing if the insulator attracts dust and small pieces of paper.

Suspend a balloon from a string and rub it with a cloth then hold the cloth near the suspended balloon. The balloon is attracted to the cloth used to charge it. Rub another suspended balloon with the cloth and see how the balloons move when held near to one another. The balloons repel each other because similar charges repel, whereas the balloon is drawn to the cloth because opposite charges attract.

ELECTRONS IN AN ATOM OF METAL

However, the outermost electrons in a metal are so far away from the nucleus that the force of attraction between them is too weak to keep the electrons circling their nucleus, leaving the electrons free to move away like smoke particles in the air. This means there is a free electrical charge in any metal even before a battery is connected. With the introduction of a battery a direction is given to the electric flow.

CIRCUITS

We treat electric current as being a flow of electrons in a circuit. When a battery is connected the positive terminal attracts the negative electrons that are free in the wires and a current flows (opposites attract!). With the help of members of the audience we construct a simple circuit to illustrate the point.

Electrons and their charges were not discovered until the turn of the last century and electron flow in wires until much later (in the 1930’s). However, a great deal of work on electricity had taken place in the previous century when it was thought that the current flowed from the positive terminal to the negative and many laws governing electrical behaviour were formulated on that belief, thus although we know that electrons flow the other way the positive-to-negative current is still used in circuit diagrams today (the ‘conventional’ current). As the distinction is not normally made at this level we mention the anomaly in the play but do not explain it in detail referring instead to electron flow.

CIRCUIT DIAGRAMS

The following circuits are demonstrated in the play and the symbols explained.

RESISTANCE

We introduce the idea of resistance as a slowing down of the current and introduce its unit of measurement, the ‘Ohm’ (after Robert Ohm). The symbol for a resistor is used.

We explore resistance further by introducing a light dependent resistor. When a light shines on a light dependent resistor its resistance decreases, allowing a current to flow ie. it is a light-activated switch and we demonstrate using volunteers from the audience.

In the classroom the idea of resistance to a current can be explored through the use of a simple circuit (shown below) and assorted materials. Test each material to see if the current can flow and light the bulb or not. Those materials that allow the current to flow are conductors; those that stop the current flowing are insulators.

Resistors are materials that restrict the flow of electricity, (even a bulb can be thought of as a resistor) and are usually specially designed for use in circuits. Often taking the form of long coils of wire or small pieces of material that do not conduct electricity very well resistors have many uses. A variable resistor can be built with a connector that slides along the coils of wire. As the length of resistance wire increases the flow of electricity slows down.

Use a variable resistor in the above circuit to explore how a dimmer switch works. What other uses could a variable resistor be put to? Resistance can be worked out by dividing the voltage by the current and is measured in Ohms:

TRANSISTORS

Although transistors are not usually studied at this level we introduce them to the audience and, using the analogy of water flowing through a tap, explain that they work in a similar way ie. they need to be turned on in order for the current to flow.

IN CONCLUSION

These notes are intended as a guide to the scientific content of the play should you wish to undertake some preparatory work. However, as the show is largely self-explanatory, preparatory work is not essential and the show will work equally well as an exciting introduction to the topic. Enjoy the show!