Electricity: Robots and electric eels
1. Start by attracting the children’s interest (Show Powerpoint Slide 1)
- Use the demo to find out what they know and to establish that they understand that the robot will not work without the battery.
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.
- 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.
Give out, one between four, bags with assorted contents as listed.
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.
Encourage the children to discuss the components and ‘wires’ used to connect up the ‘circuits’ and whether they allow electric currents to flow.
Also encourage statements such as “our circuit does not work because it does not have a ...”
3. Forest analogy (Show Powerpoint Slides 2- 6)
- Tiny particles (electrons) move round a circuit when a current flows.
From 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.
4. Thought experiment to try to imagine the size of an electron.
- The electrons are VERY, VERY tiny.
Imagine 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.
5. Circuit game (Show Powerpoint Slide 7)
- 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 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
Give 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.)
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).
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.
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).
6. Drawing circuits (If required)
- Simple circuit diagrams.
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.
7. Experiment (Show Powerpoint Slide 11)
- 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 and the bendy pencil - carbon)
To 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.
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- e.g. with the bendy pencil.
(A sheet could be given to each group to record their results but with young children a discussion works well.)
8. Demonstration using the ‘sound box’
- 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.
View apparatus list and the assembly and operating instructions for the sound box (PDF, 241 KB).
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 the contacts.
Point out that the ‘sound box’ has batteries (3V) in it so it is safe to touch the contacts.
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.
9. Electric eel (Show Powerpoint Slide 13)
- Lead into the idea that electricity can be dangerous.
These 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)
10. Mains electricity is dangerous
- Safety warnings: We conduct electric currents which can harm us.
- NEVER handle electrical appliances with wet hands.
- NEVER play with mains electricity
- Use low voltage batteries in class experiments.
Show Powerpoint Slides 15 to 20
Show 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.
11. Demonstration using the ‘sound box’.
- Some materials are neither good conductors nor bad conductors (insulators).
- These are ‘semiconductors’.
- Point out that there is a lot more to learn.
View apparatus list and the assembly and operating instructions for the sound box (PDF, 241 KB).
(Show Powerpoint Slide 21)
Discuss the change in properties and the conditions change.
- Materials with interesting conduction properties are used for numerous useful applications.
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.
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.
Using circuit with thermistor and buzzer show that the changes in conduction properties can be used as a switch to switch the buzzer on and off.
Discuss possible uses.
Children enjoy thinking out uses for sensors.
Examples that may be suggested in discussion.
Powerpoint Slide 23
They ask about LEDS because they are used in so many devices as indicators.
Powerpoint Slide 24
The discussion here will probably open up into an Q/A session with lots of ideas being proposed - using sensors
- Scientists are finding out new facts continuously and these are used to develop new ideas.
Finally 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.
- Being a scientist is exciting and interesting.
Show Powerpoint Slide 28
Explain that semi-conductor materials are used in lots of devices they enjoy using.
Computers, mobile phone, sound systems, TV, electric guitars ...
If necessary, the ending could be modified to lead into an investigation.