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Electro-magnetism

Build an electric train using:

  • Two strong magnets
  • A battery
  • Uncoated copper wire
  • A plastic tube

About

What did we do?

  • When a solenoid is connected to a voltage source, there is a current along the wire
  • There will be a constant, uniform magnetic field through the centre of the wire coil

First Attempt

First Attempt

  • Connected both ends of the wire to the battery and placed the magnets inside the coil
  • There was no interaction with the field to move the magnets
  • In a magnetic field, a north magnetic pole will be pushed in one direction and a south pole in the other
  • North and south poles are always found together, so if you just put a magnet in a magnetic field it won't move
  • The wire wasn't coiled smoothly or tightly

Second Attempt

  • Recoiled the copper wire to be tighter and smoother
  • Placed the magnets with poles facing opposite directions to create a bar magnet with north and south poles
  • As the electrical current flows through the wire, a magnetic field would be created in the section of coils in contact with the train
  • Train interacts with the north and south poles of the magnetic field to push the magnet in front and pull the magnet behind

Our Train!

Video

The

Physics

Why does it work?

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Ampere's Right-hand Rule

  • Electricity flowing through a long straight wire creates a circulating magnetic field around it
  • A field of force that will interact with any permanent magnet nearby
  • Permanent magnet will line its North pole with field lines, and will be drawn into a region with a stronger field
  • The direction of the field lines can be determined by Ampere's right-hand rule

Ampere's Right-hand Rule

  • Point the right hand thumb in direction of current along wire
  • Curl fingers inward
  • Direction of curled fingers gives the direction of the magnetic field
  • Magnetic field radiates outward in a circle
  • Its strength will decrease as the distance from the current carrying wire increases
  • If you follow along the curve of the solenoid with your thumb, the direction of the magnetic field will always be through the centre

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Magnetic Poles

  • A magnet will always have a north and south pole

  • A magnetic field can interact with magnets to cause a force upon the magnet in the field

How does this make a train?

  • A local circuit is made along the battery from the positive terminal, into the magnets, through the wire of the solenoid, and back into the magnets at the negative battery terminal
  • The magnets placed on either battery end cause the magnet poles to be pushed in and out of the circuit
  • This force causes the train to move

Pole Orientation

  • The same pole must be facing each other so the forces are in the same direction or they would cancel out and the train wouldn't move
  • If the magnetic field is non-uniform, there'll be a slightly bigger push on the north pole than the south
  • The field is strongest in the middle
  • Poles facing each other in the middle will feel a stronger push than those on the outside

Pole Orientation

Why do some work better than others?

Influences

Why do some work better?

  • Magnetic field strength is proportional to the number of turns of wire per unit length and the strength of current passing through
  • The tighter the coil, the stronger the field
  • When the magnet loses contact with the coil, the circuit is interrupted
  • Friction is not dominant drag force, the induced currents are

Conclusion

Conclusion

  • In 1820 it was demonstrated that a magnetic compass needle can be deflected by an electric current
  • Moving electrical charges produce a magnetic field
  • In this experiment, we learnt a lot about how electricity and magnetism are linked, and how each can create the other

References

References

  • http://www2.ece.ohio-state.edu/~anderson/Outreachfiles/Instructions_ElectricTrain.pdf

  • https://skullsinthestars.com/2014/12/12/the-mystery-of-the-magnetic-train/

  • http://physicsgirl.org/blog/2016/7/20/diy-electric-train-breakdown

Images

  • http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html
  • https://en.wikipedia.org/wiki/Right-hand_rule
  • https://en.wikipedia.org/wiki/Right-hand_rule
  • http://witherspoonsclass.weebly.com/uploads/2/1/0/6/21063240/8607447_orig.png
  • http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/CuttingABarMagnet.svg/540px-CuttingABarMagnet.svg.png

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