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Electromagnetism

Introduction
Public summary: 

Generate electricity and learn all about how it works!

Making electricity, and using it to spin a motor.
Useful information
Kit List: 

1. Generating power
- Small ammeter and coil. Bar magnet of some sort that fits through the hole
- Green rotating generator. Clamps to attach it to a table.
- Wooden box with bulbs/handle/generator

2. Dropping magnets
- Metal 'coin drop' setup, separate wooden base (base in box, the rest is separate)
- Two pipes, one copper, one plastic.
- Green 'iron filing' paper
- 'Stripey' magnet for use with green paper
- Selection of coin magnets (don't get more than a couple out an once).

3. Motors etc.
- Motor
- Power pack (stored in separate power pack box)
- Real motor (non-functional)
- Magnet/wire with 'indicator lights'
- Nail with coil of wire.

Packing Away: 

- Pack carefully into the appropriate two boxes (one flat blue, one small light blue).
- Put all magnets into the small tub to stop them getting lost.
- Unscrew the coin drop and store the base in the larger box.
- The power pack lives in the power packs box.

Frequency of use: 
4
Explanation
Explanation: 

There are lots of things to do, there are 2 nice stories, going through the generation and motors stuff, and some extra odds and ends. You shouldn't usually attempt to get through all of this in one go!

1. Generating Power

There are 3 different power generating bits, in increasing level of usefulness.

Magnet, coil and ammeter

This has a coil of copper wire attached to a small ammeter. When you wave a magnet through the hole in the middle of the wire you get a reading on the wire. Some things to talk about/do with it are:

  • What are the objects? Coil is made of copper wire, this is a good electrical conductor. The setup as a whole is an electrical circuit (components linked together in a circuit). The meter looks like it might measure something (cf weighing scales), it measures the amount of electrical current (or just electricity) going round the circuit.
  • Do we get more electricity by moving fast or slow? Does it work if we're not moving at all?
  • Is this very much electricity? The scale on the ammeter is microamps (the funny squiggle is the Greek letter mu), talking (or asking questions about) millimetres, metres and kilometres is a good warm-up to explaining that microamps is a small unit. Older kids might know that fuses have amp ratings on them.
  • What do the positive/negative readings mean? It tells us which way the electricity is going round the circuit, notice that it changes if we move magnet in a different direction, or swap north/south poles.
  • How can we get more electricity? Good ideas are moving faster (and moving in circles is easier than up/down), stronger magnet or more coils.

This then leads nicely onto the next bit...

Rotating generator (green)

This has most of the improvements suggested above (show to them the larger magnet, more coils), and if you spin the handle fast enough it will give you enough electricity to light a bulb. Things to talk about:

  • The faster you spin it, the brighter it is.
  • Does it matter which way round you turn it? No.
  • [more advanced]If the bulb is an LED rather than a filament bulb then it will only light half of the time, with frequency=rate of turning the handle. This is because the current is alternating ('going backwards and forwards') and it only lights when the current is going one way.

Generator in a box

This is a better version of the previous one, but it's all hidden in a box which means visitors can't see what is going on as well. There are two bulbs that can be switched on or off, and also a voltmeter/ammeter. Things to do:

  • Start someone off turning the handle and then increase the wattage of bulbs turned on gradually. They will find that it gets harder to turn as you do this. Talk about needing to put extra energy in to get more light out (the energy is coming from them, not from the magnet/coil which just convert kinetic/moving energy into electrical energy)
  • Power generation: How many watts are the bulbs you have at home? If it's this hard to turn a handle to make 10W of bulbs light, how hard would it be to power all the bulbs in your house? How about all the bulbs, TVs,... in town X? This is really where our power comes from, what better ways are there of turning the handle (wind farms are the easiest example for small kids)
  • [More advanced]Look at the ammeter/voltmeter. When a bulb is fully lit how do those readings compare to the wattage of the bulb (P=IV).

2. Dropping magnets

This uses the last part to do a neat trick.
The three columns in the coin drop are made of plastic, aluminium and metal ???. None of these are magnetic, but a coin magnet will fall more slowly through the metals.

This is because the moving magnet is inducing an electrical current in the metal (like the magnet past the coil in part 1). There are two ways to explain why this causes it to slow down:

  1. [easier]Some energy is needed to make the electrical current (like turning the handle before). This time the energy comes from the falling magnet, and when it loses kinetic energy it slows down.
  2. [harder]Eddy currents of electricity are formed, and these create an electromagnetic effect opposing the motion of the magnet, hence it slows down.

You can also do this with the perspex and copper pipes (get a volunteer to hold the pipe, with their other hand below it to catch the magnet), the slowing effect with the copper pipe is really huge.

There is also green 'iron filing' paper, which shows up the movement of a magnet through it. You can use this to 'see' the movement of the magnet inside the copper pipe.

3. Motors etc

There are various bits here, you probably won't want to do all of them. This is the opposite of what we have been doing so far. Now we are using electricity to make magnets, or electricity and magnets to make something move.

Compasses around a magnet/wire

Show what a magnet/current carrying wire do to a compass, compare the two.

Electromagnetic Nail

Wrap wire around a nail attach it to a power supply and see how it affects paper clips, with and without the power, try picking up a matchbox car as a use for electromagnets.

Jumping Wire with indicator lights

Put a current through the wire on top of the magnet, you should notice the wire is pushed by the magnet. If you reverse the direction of the current the direction of the force reverses.

Simple motor

This is a simple toy motor. There are two commutators one which keeps the polarity the same - you can show that you can get some movement but not rotation, and one which swaps the polarity, that will make it turn nicely.

-Have a look at the motor there are a load of wires near some magnets, so there will probably be some forces going on from the Jumping wire experiment.

-Using the first commutator, you need to keep swapping the polarity as when the motor gets half way round the direction of the current has essentially reversed (you are using the other half of the coil), so it gets pushed back again. You can get it to keep turning, by reversing the current. This however gets a little tedious...

Luckly the second solves the problem, everytime the motor turns halfway round the two contacts swap, so it keeps turning. This is how all DC motors work, some AC ones use the changing direction of the voltage instead of a commutator, so have fixed speeds.

Tricks: It works best on the 7.5V range with the motor wired from the +ve side to the -ve side. The brushes should be touching the commutator, on either side (top and bottom won't work)

There is a real motor in the box too, which you can compare it to.

Risk Assessment
Date risk assesment last checked: 
Mon, 01/01/2018
Risk assesment checked by: 
jaredjeya
Date risk assesment double checked: 
Fri, 12/01/2018
Risk assesment double-checked by: 
Josh Garfinkel
Risk Assessment: 
DESCRIPTION Lots of experiments about magnetism and electromagnetism
RISKS
  • 1. Overheating of coils/wire -> burns
  • 2. Powerful magnets shattering
  • 3. Rotating motor could be dangerous
  • 4. Visitor or demonstrator catching fingers in generator as they turn the handle on the generator
  • 5. Motor connections can short-circuit and get hot.
  • 6. Copper pipe hitting people in face.
  • 7. Heavy Generators and Motors could fall and hit someone.
  • ACTION TO BE TAKEN TO MINIMISE RISKS
  • 1. Do not put too much current through a coil/wire, if it is getting hot, turn it down
  • 2. Warn visitors if you give them a magnet.
    • Use the minimum number of free magnets
    • Keep the magnets under control
    • Cover with tape to reduce impact, and contain any shards
    • Pad edges of magnet to reduce finger trap
  • 3. Keep kids' fingers away - if it needs pushing it should be done on the axle, not the armature
  • 4. Place generator on flat surface so visitors can't catch their fingers underneath so easily.
    • Tell visitors to hold only the rotating part of the generator handle and not the entire handle.
    • Keep control of the visitors at all times and don't let them get overexcited while turning the handle
  • 5. Demonstrator to turn off power supply to motor when not in use
  • 6. Demonstrator should hold pipe for younger kids and monitor use for others.
  • 7. Use clamps to keep generators and motor firmly attached to table.
  • ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT
  • 1. If there is a burn, run under cold water for ten minutes, call a first aider. In event of fire, follow procedure in venue RA (raise alarm, evacuate)
  • 2. Call first aider in case of injury
  • 3. Call first aider in case of injury
  • 4. Call first aider in case of injury
  • 5. Turn off electricity at mains. Call first aider in case of injury. In event of fire, follow procedure in venue RA (raise alarm, evacuate)
  • 6. Call first aider in event of injury.
  • 7. Call first aider in event of injury.
  • This experiment contains mains electrical parts, see separate risk assessment.
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