ElectricityRobots and electric eels

Supports National Curriculum, Key Stage2, Units 2F, 4F and 6G

Suitable for years 4,5 and 6.

The time for whole session is about 1 ½ hours. This can be varied by taking shorter paths through the material. Choices may depend on the apparatus available or the particular needs of the class.

Outline of contentAims to

- establish what the children already know, using demos and class experiments- investigate simple circuits through class experiments and deduce rules for a current to flow.- provide a clear analogy of conduction and electric circuits through a game - show some materials are conductors and others are insulators through class experiments- investigate the conductivity of materials including water and semi-conductors using a ‘sound

box’- provide guidance for safe use of electrical appliances in the home- show that some materials can change their conductivity and explore uses - demonstrate and discuss up-to-date applications by linking the children’s knowledge with

their experience.

Points to note:Please read the notes the safety notes at end of this document.

Cross References- The slides in the PowerPoint presentation are referenced in the table and have

commentary notes.- As the presentation may be running throughout the session some simple slides provide a

suitable background, alternatively switch to a black screen.- Apparatus details are below the table and are linked to the relevant sections.- Notes about safety are below the table

VocabularyThe presentation uses expressions included in the KS1&2 strategies http://www.standards.dfes.gov.uk/schemes2/science/?view=get

Misconceptions which are to be corrected- When a circuit is completed, the current (electrons or particles carrying charge) pours out of

the battery and round the circuit. - When the current stops flowing the electrons all go back into the battery.- Materials are either very good conductors or very good insulators.- It is safe to operate mains switches with wet hands.- The physics that they learn is not relevant to their everyday lives.

I found that the children had lots of ideas to contribute and were fascinated. I therefore allowed the discussions continue and answered numerous questions so that the sessions took whole afternoons. Teachers, in each school, commented that the whole group was interested and took part fully. The schools which were visited had very different characters and the total ability range was very wide.

Electricity : Robots and electric eels

Activity Discussion Aims/facts1. Start by attracting the children’s interest.(Show Powerpoint Slide 1)Show a toy robot e.g. one that can climb windows or smooth surfaces and has a flashing lamp.

Ask them how the robot can climb the window. Some may correctly say it has suckers on its feet. If they start from this point ask how it moves and then how upwards. Encourage answers including- electricity, battery, motors, circuits, lamp ----

Use the demo to find out what they know and to establish that they understand that the robot will not work without the battery.

2. Experiment Give out, one between four, bags with assorted contents as listed.

See Apparatus List

Some will have components to make a complete circuit- others will not. As you hand them out explain that some of the groups may not be able to light the bulbs. After this collect all apparatus in the original bags.

View Safety Notes

Encourage the children to discuss the components and ‘wires’ used to connect up the ‘circuits’ and whether they allow electric currents to flow. They should Also encourage statements such as “our circuit does not work because it does not have a -- ”

To light a lamp a battery and a complete path (called a circuit) made of conducting material are needed.

Note: this activity may be revision.

3. Forest analogy Show Powerpoint Slides 2 to 6From high above a forest, the trees look like an almost smooth surface, from lower down the trees are seen and from even lower monkeys can be seen which move between the trees.

Ask the children to think about what is happening in a metal.Explain that there are spaces in the metals (like between the trees) that very, very tiny particles can move through. Help them to visualise how small the particles are by discussing huge numbers. They may suggest a million. Clarify that they understand this is 1000 lots of 1000--- about the number of people on Merseyside or in a city near them.

Tiny particles (electrons) move round a circuit when a current flows.

4. Thought experiment to try to imagine the size of an electron. Image a pin head. Then talk about each of a million people putting one tiny dot along a line on the pin head. Explain that it is very difficult to image such tiny dots but they are far, far larger than the particles moving through the wires. Even if a million dots are put on one of these tiny dots, they would be much larger than an electron.

Explain that the particles moving round the circuit are called electrons.

Encourage the children to discuss the problems of imagining such large numbers and such tiny dots and explain that everyone has this problem – they are far too small to see. Link back to the idea that from an aeroplane they would be unable to see the monkeys moving between the forest trees.

The electrons are VERY, VERY tiny.

5. Circuit game

See Apparatus List

Show Powerpoint Slide 7Give every child a piece of scrap paper and ask them to crush it into a small ball. Ask them all to stand in a large circle. (It is best to arrange where this will be before the session.)

Point out that every child has a ball at the start. The balls do not all start in one place. When you say ‘stop’ each should still have a ball. Some practice is usually needed and enjoyed. Once they can do this, discuss what is needed to start the electrons moving round the circuit.

Whether the current is flowing or not, the electrons are all around the circuit.

Reinforce that a complete loop is needed for the electrons to flow.

When a current flows the electrons move round

Every child should hold the paper ball in their left hand. On the count of ‘1’ each child should take the ball in their right hand and on the count of ‘2’ put it in the left hand of the child next to them. This is repeated as you say 121212--- until you say ‘stop’.

Put a paper hat on showing a battery. Put the ‘lamp hat’ on a child. Also arrange that the teacher will shout “stop!” after the ‘current’ has been flowing for a while. (upper size of children in ring is about 20 - others could watch)

You represent the battery because you are saying 121212—so that the current flows. The teacher is a switch – which will need discussion. The child with the lamp-hat (or another child standing behind) should rotate it to show the unlit lamp when the current stops flowing.

Powerpoint Slide 8

the circuit and the lamp lights.

A switch can be used to break the circuit so that the current stops and the lamp goes out. The electrons do not all rush back to the battery.(Be careful not to imply that the electrons stop moving completely.)

6. Drawing circuits(If required )Show Powerpoint Slides 9 and 10

Discuss the problem of drawing pictures to represent the components. Symbols do not need labelling and are easier to draw.

Simple circuit diagrams

7. Experiment

See Apparatus List

Show Powerpoint Slide 11To each group of 4 children, hand out a bag of components which form a circuit to light a lamp.Also hand out a collection of items made of different materials. Ask the children to complete the circuit to light the lamp and then disconnect the circuit at one point and connect in an item made of a material to be investigated.

View Safety Notes

Discuss which items are good conductors.Discuss the materials the items are made of.Point out that the lamp is not bright in some cases- eg with the bendy pencil.(A sheet could be given to each group to record their results but with young children a discussion works well.)

Metals are good conductors, most other materials are insulators (materials which do not allow electricity to flow through them).Some materials allow electric currents to flow through them and are not metals (e.g. the pencil bendy pencil - carbon)

8. Demonstration using the ‘sound box’.

See Apparatus List and the pdf of assembly and operating instructions for the sound box.

Show that better the conductor the higher the pitch. Reinforce this using the demo buttons on the sound box.Text a good selection of materials including both a 30cm and a 3m bendy pencil.

Show that water is a conductor and when salt is added the pitch is raised.Explain that people conduct electricity. People work by tiny currents flowing round their bodies.

(Show Powerpoint Slide 12)

Hold a contact of the sound box in each hand and listen to the note. Then increase the grip on each contact, then dampen fingers and grip

Discussion about the frequencies of the sounds heard. Encourage them to explain what they understand from the sounds heard. Link with their music knowledge if appropriate.

Discuss the sounds heard in each case.Ask a different child to help with each activity.

Ask for a volunteer to test if people conduct electric currents.

Voltage can be described as an electrical ‘push’ but only mention it if necessary.

Some good conductors are better conductors than others.

Water is a conductor.

Salty water is a better conductor than tap water.

People conduct electricity—wet hands cause a better contact.

the contacts.

Point out that the ‘sound box’ has batteries (3V) in it so it is safe to touch the contacts.9. Electric eelShow Powerpoint Slide 13These give their prey an electric shock to stun them. Show Powerpoint Slide 14 They live in water that is a conductor.

Discuss electric eels seen at large aquaria. Ask if they remember the eel causing lights to flash. (Note: the electric eel is a fish, not a true eel, found in the Amazon River Basin, South America)

Lead into the idea that electricity can be dangerous.

10. Mains electricity is dangerous. Show Powerpoint Slide 15 to 20Show slides indicating that wet hands made good electrical contact.

Explain that during class experiments batteries are used. Show pictures of bathroom light cord.

Discuss why we do not have wall mounted light switches and sockets in the bathroom.

They enjoy this but it is probably better to keep the discussion away from horror stories which they will relate.

Safety warnings - We conduct electric currents which can harm us.NEVER handle electrical appliances with wet hands. NEVER play with mains electricityUse low voltage batteries in class experiments.

11. Demonstration using the ‘sound box’.

See Apparatus List and the pdf of assembly and operating instructions for the sound box.

Show Powerpoint Slide 21a) with LDR- show effect of

covering and uncovering the LDR

b) with thermistor- show effect of warming the LDR

c) with LED- show effect of reversing the contacts

View Safety Notes

Discuss the change in properties and the conditions change.

Some materials are neither good conductors nor bad conductors (insulators).These are ‘semiconductors’.

Point out that there is a lot more to learn.

12. Demonstration See Apparatus List

a) using a circuit with LDR and a LED show that the changes in illumination causes changes in conduction properties which can be used as a switch to switch the LED on or off.

b) variations are possible in the combinations of components according to availability. The circuit above with a buzzer instead of the LED works well. Adjust the potentiometer so that in full room light the buzzer is silent. As soon as the circuit was in partial shade the buzzer started to sound. When it was covered it sounded loudly.

c) using circuit with thermistor and buzzer show that the changes in

Discuss possible uses.Children enjoy thinking out uses for sensors.

Examples that may be suggested in discussion. a) a freezer high temperature warning

b) automatic porch lights and street lamps. (Powerpoint Slide 22)

c) They will ask about other uses and suggest ideas. (Powerpoint Slide 23)

d) They ask about LEDS because they are used in so many devices as indicators. (Powerpoint Slide 24)

e) The discussion here will

Materials with interesting conduction properties are used for numerous useful applications.

conduction properties can be used as a switch to switch the buzzer on and off.

View Safety Notes

probably open up into an Q/A session with lots of ideas being proposed- using sensors.

13. ApplicationsFinally show slide of traffic lights which use LEDs and suggest they look out for them.Show Powerpoint Slide 25

Explain that the development of LEDs for traffic lights is recent and they last longer and save money ---(When one LED fails the signal continues to function. The signals need replacing much less frequently and even 100 LEDs draw less current than a big filament lamp so saving money.)Or lead into another example of an up-to-date application that they can understand.

Scientists are finding out new facts continuously and these are used to develop new ideas.

14. Re-cap 15. EndingShow Powerpoint Slide 28

Explain that semi-conductor materials are used in lots of devicesthey enjoy using.Computers, Mobile phone, Sound systems, TV, Electric guitars----

Being a scientist is exciting and interesting.

InvestigationIf necessary, the ending could be modified to lead into an investigation.

List of apparatus

Electronic components may be purchased form Maplin, RS or other suppliers

1. Start Robot e.g. Climbatron - walks up windows etc Or any electrical toy or gadget which is large enough for the class to see and will catch their

interest.

2. Experiment Provide a variety of items for the children to use to try to light the lamp bulbs. If assortments of items are put into bags, then they can be handed round quickly.

If conventional leads and battery holders are not available, the following is a cheap alternative which is quick for the children to connect:

Pack of magnetic connectors - bought in a pack of 10 pairs. Pack of test leads. These have a crocodile clip at each end. MES bulb holders MES bulbs (1.25 V, 250 mA). 1.5 V batteries (avoid alkaline or high power cells) Fishing pole elastic and other insulating cords which resemble insulated wire. Crocodile clips

Cut a test lead into two. Bare the cut ends and connect to the bulb holder.Magnetic connectors can be used to connect the battery into the circuit. These consist of a small magnet attached to a wire and are bought in packs of ten pairs. The magnet can be attached to the battery terminal and the children can attach the wires to the crocodile clips to complete the circuit.Connect some of the bulb holders to lengths of fishing elastic with crocodile clips and others to lengths of other cords. At first glance the cords should all appear to be insulated wires.

Bag type 1 (Make enough of these for 1 bag between about 4 children because they will be used again in activity 7.)Circuits which will light the lamp.

1.5 V battery pair of magnetic connectors bulb bulb holder with conducting leads and crocodile clips

Bag type 2which will not light the lamp

1.5 V battery pair of magnetic connectors bulb bulb holder with insulating ‘leads’ attached and crocodile clips.

Bag type 3Variations on the above two bags with items missing

NB The fishing pole elastic looks exactly like insulated wire but children soon notice its elastic properties when the lamp does not light. (Available from fishing tackle shops and useful for demos for other topics)

5. Circuit game 1 sheet of scrap paper per person a paper hat with a bright lamp on one side and an unlit lamp on the other a paper hat with a picture of a battery on it.

If the hats are made with a band fastened by strong paperclips they can be adjusted to fit.

7. Experiment Bag type 1 as in activity 2 (a bag between about four children) Collections of everyday articles made of different materials.

E.g. wire coat-hanger, metal spoon, wooden spoon, plastic spoon, cooking foil, rulers, paper plate, etc.

pencil sharpened at both ends 30cm ‘bendy’ pencil with the plastic removed for a length close to each end to expose the

coreSimilar articles made of different materials help the discussion. Aim to include colourful articles which are quite large.The children can also use their own items.

8. Demonstration using the ‘sound box’

Sound box Samples of materials 30cm bendy pencil and 3m bendy pencil (obtainable from shops selling tricks and gadgets.) 1 litre bottle of water (to save having to obtain water before start of session) 2 large transparent plastic beakers Contacts (or probe as in picture) Small pack of salt Stirrer

11. Demonstration Sound Box Thermistor, mounted LDR, mounted LED, mounted

12. Demonstrations These circuits are much cheaper, quicker and easier to construct than the sound box they provide examples of semiconductors as sensors.

Circuit using a LDR to light a LED when it is dark.

Alternatively, the LED can be replaced by a buzzer so that a noise is made as the LDR is covered or the light intensity falling on it is reduced. Variations on the circuit can be constructed according to availability of components.For example the LDR may be replaced by a thermistor to light the LED when it is cold.In each case adjust the potentiometer so that a small change in the conditions causes the semiconductor device to be switched on or off.

The circuit was wired inside a plastic container so that it was possible to switch on and adjust the potentiometer but children could see only the LDR and buzzer or LED.Components

6V battery 10 kpotentiometer LDR (e.g. Maplin N59AY) Buzzer (e.g. Maplin KU56L) LED - various

(If it is not possible to construct a ‘sound box’ then these can replace much of activities 8 and 11.)

Safety notes

Possible hazards to be discussed with the teacher BEFORE the visit:

a child short-circuiting a battery so it or a wire becomes hot – the risk of harm is reduced by the choice of cell type. Avoid alkaline or high power cells.

a child catching a finger on a crocodile clip - use the miniature ones with plastic covers which cannot open very far.

A child swallowing a button magnet - check that the magnets in the magnetic connectors (if used) are securely in place before use.

Injury from items to test for conductivity – check that they are not sharp (eg a wire coat-hanger hook should be bent round or taped)

The 'sound box' and other electronic circuits must be constructed so that they do not present a hazard if they are handled by the children.