Sweet circuits & circuit diagrams/symbols

Transcription

1 Sweet circuits & circuit diagrams/symbols (Physicist-led activity) This activity models electrical circuits using pupils to represent charges/electrons travelling around a (~10ft x 10ft) rectangular circuit marked out using tape on the floor. Each child is given one or more sweets, representing energy, by a pupil representing the battery and gives these up to a lamp pupil. Note: It is better to talk about how hard/easy it is for an electric current to flow and avoid mentioning speed of flow as this leads to misconceptions in years to come. Demo circuit for introduction - using a battery, switch & two lamps connected by wires with croc clips. A large rectangle marked out on the floor using Masking/Duct tape (with a battery/gap for the battery pupil and a switch/gap for a one, or two, pupil switch ) Sticky labels with for electron pupils A4 coloured labels with circuit symbols to be hung around the necks of 2x battery, 2 x lamp and 1 x switch pupils. Note: The switch label should be double-sided, with open switch symbol on one side and closed switch symbol on the other. Labels could be laminated with a neck string joining two corners of the landscape sheets. Wrapped sweets e.g. boiled fruit sweets or Cadbury éclair sweets (Optional) Large A3 circuit diagram sheets showing a series and a parallel circuits for explanation (Optional/ KS3) Stop clock to explain that current is the no. of electrons passing a point in a given time. (Optional) A BIG circuit long wire between battery and lamp) 1. Show the class a demo circuit containing a battery, switch and lamp in series. Explain what each component does and how they are connected by metal wires (covered in insulating plastic). 2. Explain that scientists represent this equipment using a circuit diagram, drawing straight lines for wires and using simple symbols to represent the components in the circuit. Introduce the taped circuit on the floor. 3. Remind them that electricity is the flow of electrons around a closed/complete circuit (as discussed in introduction), describe electrical current as the movement of electrons around a complete circuit. Write the words ELECTRON and CURRENT on a whiteboard. 4. Ask two volunteers to be the battery (A4 labels) and several others to be electrons who will spread out and walk round the circuit, from negative side to positive side of battery. Note ALL electrons start moving at once, with a LITTLE push from the battery on the electron closest to the negative terminal of the battery. If you want you can label the electrons with a - sticker/badge. 5. Electrons can only flow if the circuit is complete. Ask for one or two volunteers to represent the switch. (you can either use one volunteer wearing the open/closed switch label or use two volunteers who link hands to make switch). The electrons move when the A4 label is one way round / hands touch and not when it is the other way round / not touching. (Optional/KS3 you can use a stop clock to measure the number of electrons that pass a particular point in one minute and relate this to the electrical current in the circuit. Using two stop clocks, you can explain how the current is the same everywhere in a series circuit.) 6. Introduce one volunteer who is a lamp/bulb in the circuit. Lights change electrical energy (provided by the battery) into light energy given off to the room. Model the energy by each cell of the battery supplying each electron with one sweet, which it carries around the circuits and gives to the bulb, who throws the two sweets per electron into a tray. 7. Introduce the concept of two bulbs in series using a second bulb volunteer. Each bulb is given one sweet by the electrons and gives this amount of energy out (tosses sweet into tray). Show what happens when you put two bulbs in your demo circuit dimmer than before. 8. Time permitting, introduce parallel circuits, using an extra strip of tape to provide a second path along which the electrons can alternatively flow. Now each electron chooses one of two paths and gives both sweets (all its energy) to the bulb in that path. Show no reduction in brightness (when parallel bulbs compared with one bulb) using demo circuit. 9. Pupils complete page 1 of Workbook Three lamps in series all dimmer still What if wires really long? The electricity does NOT get to one lamp before another they all light at once since ALL THE ELECTRONS MOVE AT THE SAME TIME. This common misconception needs correcting.

2 Investigating which materials conduct (Teacher led activity) This activity involves a teacher managing their pupils themselves. Pupils work in groups of 2 or 3, putting together a simple circuit and investigating whether particular materials/objects as part of the circuit light a lamp, i.e. conduct electricity. Circuit sets (one per 2/3 pupils), each of which comprises: o A battery in a battery holder (or with wires held firmly to each battery contact using a rubber band or sellotape). o A filament bulb in a holder with either connection screws or 4mm plug connections. If one 1.5V battery used this should be a 1.5V lamp: If up to four cells used then this should be a 6V bulb. o Three leads with 4mm plugs or wires o Two six crocodile clips per pair of pupils (depending how your leads/wires attach) Strips of various materials & various objects to test A split 4B pencil (Staedtler Art 1104B works for me using a 1.5V filament bulb the lamp is bright when the contacts are close, but off when the full length of the pencil is used). For extension activity. 1. The teacher should remind pupils that electricity is the flow of electrons around a closed/complete circuit (as discussed in introduction), using the cosmic ball and a ring of ALL pupils in the group as the activity starter to gain confidence talking about electrical circuits, and involve everyone. 2. The teacher should remind pupils that we need a complete circuit, and that all parts of the circuit must be made up of materials that electrons can flow through. These materials are called (electrical) conductors. Write CONDUCTOR on the whiteboard. (Optional: Ask what the opposite of a conductor is called something that electricity cannot travel through Insulator. Write on whiteboard) 3. The teacher should then demonstrate the investigation on page 2 of the workbook using only ONE of the materials provided to complete the circuit. 4. The teacher should then explain that pupils will work in pairs to construct the circuit by CAREFULLY using the equipment provided, sort out the groups and oversee the activity. 5. If time, pupils should carry out the extension activity with the split pencil. (see below) 6. Pupils MUST return equipment to where they found it and leave it in tidy order before they can move on to the next activity Make a dimmer switch using a pencil lead Same circuit as above, but also with 4B pencil split down its length (and pretested to check lamp is bright when contacts very close and dims when they are moved apart say 5-15 cm). Also a 15cm ruler is useful for quantitative measurements.

3 Resistance & rope circuit model (Physicist-led activity) This activity models resistance in an electrical circuit. Note: It is better to talk about how hard/easy it is for an electric current to flow and avoid mentioning speed of flow as this leads to misconceptions in years to come. 5-10m long Rope, tied in a loop (optional) A4 Battery, bulb labels and electron stickers/badges) Whiteboard & pen Multimeters & leads (one between two/three) Bowl of water & a hand towel (or get the pupils to lick their fingers!) For Extension activity: 1/2 play tunnels or tables that the pupils can crawl under, 2 trays/boxes, Sweets Remind the pupils that electricity is the flow of electrons around a closed circuit (as discussed in introduction) and explain that we can model electrons using little people or balls. Ask what happens if we put a light bulb in the way of the electrons. Introduce the idea that electrons lose energy when they pass through the bulb introduce RESISTANCE and write this on the whiteboard. Explain that a light bulb is a resistor because it resists the flow of electrons. Make an analogy between resistance and friction (or carry out this activity and ask the children what it has to do with electricity and draw out their thoughts). Draw a series circuit on a whiteboard and ask the pupils to join in a game where we use a rope loop and one pupil/the teacher is the battery and one or more pupils are lamps. In this model the children stand in a circle holding the rope loop lightly in their curled fingers. The battery starts the rope moving by pulling it with one hand and feeding it through the other. The lamp pupils grip the rope lightly, so they can feel the friction at it moves (but not so hard that they burn or stop it moving). The electrons are represented by the rope moving around. Energy is introduced into the circuit (Energy IN) by the battery, and transferred to the surroundings (Energy OUT) as heat where there is a resistance to the rope, and by analogy the electrons, moving. Now ask the children to put the rope, battery and lamp labels down on the floor and take a step back. Explain that not just lamps are resistors, other things can be too (like appliances). Talk about resistive heating and how it is sometimes useful (toasters, heaters, kettles etc) and sometimes just wastes energy (pylons, filament lamps, computers/mobiles/chargers getting hot). Explain that the human body is also a resistor and this is why playing with mains electricity is so dangerous. The electrons can flow through your body and can cause a lot of damage and even kill you! Tell them that we are going to measure our resistance (in a safe way). Show the pupils the multimeters. Does someone know what they are? Show them how to: Switch the dial to 2000k in the Omega ( ) / Ohms section (bottom left ~ 9pm on a clock ) Plug one lead into the black/com socket and a second into the V ma socket. See what the screen says (if you get a 1, move to scale to a higher value of Ohms) Complete page 3 of the workbook using multimeters to measure your resistance and that of two friends, try repeating this with wet hands/licked fingers. If you have time, place play tunnels (or tables that pupils can crawl underneath) at the same point as the lamps and a tray/box of sweets at the same place as the battery. Ask the pupils to represent electrons and stand on the rope. Give those between the battery and the lamp a sweet. Explain that the pupils will move along the rope, going through the tunnel, where they must drop off any sweets that they are holding into a second tray/box, go through the tunnel and return, along the rope, to the battery where they pick up a sweet. The tunnel slows them down. You can go on to discuss and model even more stuff: Adding another resistor in a series circuit Add another tunnel in series with the first to make them even slower. Note: all electrons should still be moving at the same rate everywhere in the circuit. Parallel circuits & the total resistance reducing if more than one path. Use motorway toll booth /supermarket checkouts analogy and how fast you can pay. Model using two play tunnels in parallel with each other. Blocking/disconnecting wires along a path in the case of a series & a parallel circuit. What happens if a tunnel blocked in the models above? What type of circuit would you have the room lights in your house/this building connected in?

4 Batteries and Making a fruit battery (Teacher-led) In this activity the pupils will connect a lamp/led to two lemons in series and show that they can get this to light up, therefore it acts as a battery/power source. They will then have the opportunity of testing with other fruit, more or less fruit, other metals for the connections, etc. (see p4 of the workbook) plus some multimeters and calculators for the extension activity. 1. BEFORE YOU START: Make sure you know where the knife is to be able to cut slits in the fruit and so no pupils get hold of it. 2. The teacher should remind pupils that electricity is the flow of electrons around a closed/complete circuit (as discussed in introduction), using the cosmic ball and a ring of ALL pupils in the group as the activity starter to gain confidence talking about electrical circuits, and involve everyone. 3. The teacher should ask Where does the electrical power come from in an electrical circuit? and draw out responses like batteries, cells, sockets, wind up torch, mains, solar cells, etc). These all have a Voltage associated with them which tells us how much energy is given to each electron/charge. Write VOLTAGE on the whiteboard. 4. Ask a pupil to read out the first paragraph of p4 of the workbook and circle the objects that store/provide electrical power on their workbooks. 5. Explain that you are going to make a power supply/battery using fruit! Ask another pupil to read out what you need and hold up/talk about each item. 6. Demonstrate each step of the instructions in turn. Note: The zinc nails are the ones with the big heads! 7. Ask a pupil to read out the paragraph just above the table and explain how they are going to complete the table recording their results like proper scientists/experimentalists! 8. Now divide the pupils into groups of two or three and get them to follow the instructions themselves to make a 2-lemon battery light a lamp/led. When they have done this and shown you, they can experiment freely themselves (without going wild!) 9. Please MAKE SURE THEY TIDY UP BEFORE MOVING TO NEXT ACTIVITY 10. Complete the last part of page 4 of the workbook, including using a multimeter to measure the voltage of their battery. To do this: Switch the dial to 20 DCV section (top left 10pm on a clock ) Plug one lead into the black/com socket and a second into the V ma socket. See what the screen says (if you get a 1, move to scale to a higher value of DCV)

5 Static electricity (Part self-guided, part Physicist-led) This activity could be used either for pupils who finish before time or for an additional activity in the circus if thee are five groups of pupils. Lots of small pieces of paper (holes from a hole punch?) A comb Balloons (preferably long ones as these have a greater surface area in contact with a wall etc.) A Perspex school laboratory safety screen Two balloons on strings/cotton hung from ceiling Two strips of carrier bag. Polythene and perspex rods balanced on a watchglass on a small upturned beaker. Clean dusters Van Der Graaff machine and tray of bits and bobs! Plasma ball Fun fly stick See page 5 of workbook.