IOP Institute of Physics

Apparatus

Electricity generation Part 1

Activity 1:
Balloons
Bring some that are not very difficult to blow up and also some that are much harder to inflate so that children helping with this will begin to feel tired.

Activity 2:
Show a selection of mechanical toys, musical instruments and tools.

Choose examples that you have available that clearly need energy for them to work.

Examples:

• Toys – any wind-up toys, musical box, party blower, etc
• Musical instruments – drum, wind instrument, etc
• Tools - hand whisk, hammer etc

Activity 6:
Circuit Game to show how electricity carries energy.

• Large bowl
• Large bag of large pasta pieces eg ??? – uncooked!
• Metal pan or container
• Lid arranged so that when a piece of pasta is dropped on it a sound is heard

To play:

• The children stand in a large circle. You explain that they represent tiny particles (called electrons) in the wire in a circuit.
• The bowl of pasta represents the battery. This should be placed on a chair or table at one side of the circle.
• The pan and lid represents an electric bell.
• When you say “switch on” the children should move round the circle. They should pick up a piece of pasta (energy) as they pass the bowl and then drop it on the lid as they pass the pan.
• The energy from the battery is used to make the sound.
• When you say switch off, they should stop moving.
• Pasta is chosen because it is food, which contains energy.

Activity 11:
Lemon battery – see Section 2 for full details

• 5 - lemons
• 5 - 2p pieces
• 5 - zinc coated nails about 4cm long
• 6 - leads with a crocodile clip at each end
• 1 - red LED – ( eg a 5mm super-bright red LED) It is useful to have spares.

Cut a slot in each lemon and insert a 2p piece. Stick a nail in the lemon approximately 1cm away from the 2p piece making sure the coin and nail do not touch.

Use a lead to connect the nail to the LED using the wire nearest the small flat face. (This is the negative side of the LED.)

Use a second lead to complete the circuit by connecting the 2p to the other wire from the LED.

The LED will not light.

Add more lemons as described in detail in section 2 of this file - with the class watching.

When 4 lemons are in the circuit (with the 2p pieces connected to the nails) the LED will light.

Activity 14
Model generator – see Section 3 for full details

• Length of enamel coated copper wire (~12m x ~0.45 mm diameter)
• Short length of plastic tube (~20mm diameter x ~80mm length)
• Magnets (e.g. 6 Neodymium Iron Boron, 12mm diameter by 2 mm thick.

Alternatively rod shaped magnets are available which are magnetised at right angles to the longer dimension.)

Magnets are available on the web.

• Insulating tape
• Clear sticky tape
• Rubber bung
• Thick card
• A super-bright red LED (plus a few spares)
• Glue
• Soldering iron and solder

Exploded diagram of model generator

A coil of wire is wrapped round a tube and the ends of the wire are connected to a red LED.

Full details for the assembly are in section 3. The tube should be shaken so the neodymium iron boron magnet moves along the axis of the tube. When the direction of polarisation of the magnet is parallel to the direction of movement, the magnetic field cuts the turns of wire in the coil as the magnet moves.

Activity 18
Show examples of small hand generators which are shaken or wound up.

e.g.

• Wind-up torch
• Wind-up phone charger

All widely available on the web.

Explain that the energy you supply from your food is used to charge up the devices. The electrons then carry the energy to where it is needed.

Section 2

Construction of a Lemon Battery
A battery consists of two different metals placed in an acid. The two metals then form the terminals of the battery. For school demonstrations it is important to use a very weak acid. Vinegar is usable but possibly too messy. In this demonstration the citric acid in lemons is used.

A good choice for the two metals is zinc and copper. For the former galvanised nails can be used, for the latter copper wire or suitable coins, here 2p coins are used. I cleaned the coins and nails before use by rubbing them briefly with some wire wool.

With one lemon the voltage produced is approximately 0.74V as shown in the following figures.

This is insufficient to light the LED which requires approximately 2V (a red LED should be used as this requires a lower voltage than do other colour LEDs. For the present demonstration a 5mm super-bright LED was used).

Connecting two lemon batteries in series increases the voltage to ~1.7V.

This is still insufficient to light the LED. Hence at least three lemon batteries connected in series are required.

Three lemon batteries give a voltage of ~2.6V and this is sufficient to cause the LED to light dimly. The final zinc nail should be connected to the lead on the LED which has a small flat against it. Normally LEDs need a series resistor to limit the current but this is not needed here as the maximum current that the lemon battery can supply is very low.

Increasing to four lemons gives a voltage of about 3.6V and this produces sufficient current to light the LED reasonably brightly.

Connecting five lemons in series was also tried but this didn’t give any noticeable increase in the brightness of the LED.

Although three or more lemons produce sufficient voltage to light the LED they are not able to supply a large current. This is a result of their large internal resistance. It might be possible to increase the current by using larger pieces of metal (particularly the zinc) and experimenting with how far apart they are placed in the lemons (they must not touch each other directly).

Section 3

Construction of a Hand Held Generator
Items required

• Length of enamel coated copper wire (~12m x ~0.45 mm diameter)
• Short length of plastic tube (~20mm diameter x ~80mm length)
• Magnets (Neodymium Iron Boron 6x 12mm diameter by 2 mm thick)
• Insulating tape
• Clear sticky tape
• Rubber bung
• Thick card
• Super-bright red LED
• Glue
• Soldering iron and solder

Construction details

• Cut a length of tube approximately 80mm in length. The diameter is not critical but ideally the internal diameter should be slightly larger than the diameter of the magnets to allow them to move freely but not rotate. It is probably possible to make a suitable tube by rolling up a piece of cardboard.
• Cut two thick cardboard washers with internal sizes sufficient to give a tight fit onto the tube. Position these washers so they are approximately 20mm apart and equally spaced either side of the middle of the tube. Fix in position using suitable glue.
• Use a pin or needle to make a small hole in one of the washers close to the plastic tube. Pass the end of the copper wire from the space between the washers through this hole so approximately 200mm extends through to the other side.
• Wind the copper wire around the tube so it fills the space between the two washers. The precise diameter of the wire is not important although if too thick only a limited number of turns can be wound, if too thin many turns can be wound but the electrical resistance may be too large. The prototype used wire of diameter ~0.45mm. It is important that this wire has an enamel coating for insulation. You may need to experiment with the number of turns but ~500 should be sufficient.
• When sufficient turns have been wound cut the wire to leave a free length ~20mm and hold the wound wire in place using clear sticky tape (so that the wire can be seen).
• Remove the enamel insulation from the final ~5mm of the two ends of the wire (scrape off using a sharp knife or remove with fine sandpaper) and solder the two wires to the leads of the LED. Red LEDs require lower voltages to operate and the use of a super-bright type should allow the light produced to be visible in a bright room. Use insulating tape to wrap around the leads of the LED to prevent them from touching.
• Use insulating tape and a small piece of card to block up one end of the tube. A rubber bung in the other end allows the magnet to be removed during demonstrations to show that the generator does contain a magnet. Place the magnet (or magnets in the tube) and fit the rubber bung. The flat face of the magnet should be perpendicular to the axis of the tube. The choice of magnet is not critical. The prototype used six 12mm diameter by 2mm thick magnets held together by their intrinsic fields. Other combinations would work although they need to be high strength type (e.g. Neodymium Iron Boron). When the tube is shaken so that the magnets slide rapidly from one end of the tube to the other, sufficient voltage should be produced in the coil to cause the LED to flash brightly. Brighter flashes are produced with the magnets inserted in a particular direction, once this direction has been determined mark the appropriate face of the magnet so the correct orientation can be retained during demonstrations.