Investigating Conductors & Insulators (Cambridge O Level Physics)

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Conductors, Insulators & Electrons

  • The key difference between conductors and insulators is that:
    • Conductors allow charge carriers to freely move
    • Insulators do not allow charge carriers to move
  • The reasons for this are to do with their internal structure

Conductors

  • A conductor is a material that allows charge (usually electrons) to flow through it easily
  • Examples of conductors are:
    • Silver
    • Copper
    • Aluminium
    • Steel
  • Conductors tend to be metals

Relative Conductivity of Different Materials

Conductors and insulators, downloadable IGCSE & GCSE Physics revision notes

Different materials have different properties of conductivity

  • On the atomic scale, conductors are made up of positively charged metal ions with their outermost electrons delocalised
    • This means the electrons are free to move

  • Metals conduct electricity very well because:
    • Current is the rate of flow of charged particles
    • So, the more easily electrons are able to flow, the better the conductor

Metallic Bonding and Delocalised Electrons

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The lattice structure of a conductor with positive metal ions and delocalised electrons

Insulators

  • An insulator is a material that has no free charges, hence does not allow the flow of charge through them very easily
  • Examples of insulators are:
    • Rubber
    • Plastic
    • Glass
    • Wood

  • Some non-metals, such as wood, allow some charge to pass through them
  • Although they are not very good at conducting, they do conduct a little in the form of static electricity
    • For example, two insulators can build up charge on their surfaces. If those surfaces touch, this would allow that charge to be conducted away

Investigating Electrical Conductors & Insulators

The Gold-leaf Electroscope (GLE)

  • To distinguish between conductors and insulators a Gold-leaf electroscope (GLE) can be used

Gold-Leaf Electroscope

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The gold-leaf electroscope is a device used to demonstrate charge

  • The GLE consists of
    • A metal plate attached to one end of a metal rod
    • At the other end of the rod a very thin leaf of gold foil is attached
    • The rod is held by an insulating collar inside a box with glass sides, allowing the gold leaf to both be seen and protected from draughts
  • When the GLE is charged, the plate, rod and gold leaf have the same charge (either positive or negative)
    • Since the rod and leaf have the same charge, they repel, and the leaf sticks out to the side
    • When the rod and leaf are discharged (are neutral) the leaf hangs down

To Test Electrical Conductors and insulators

  • Charge the plate of the GLE so that the gold leaf stands clear of the rod
  • Carefully touch the plate of the GLE with the items being tested, for example:
    • Metals, such as: wire, paperclip, scissor blades
    • Non-metals, such as: paper, fingers, glass, graphite
    • Plastics, such as: plastic ruler, the handles of the scissors, finger in a plastic sandwich bag
    • Comparisons, such as: wet cloth, dry cloth; finger and finger in a plastic sandwich bag
  • Record the observations each time
    • Leaf falls: material is a good conductor
    • Leaf remains in place: object is a poor conductor (good insulator)
    • Leaf falls slowly: material is a poor conductor

 

Alternative method

  • An electronic charge detector can be used in place of the Gold-leaf Electroscope

Expected Results

  • Overall, metals are very good conductors whilst non-metals tend to be good insulators

Conductors & Insulators Summary Table

Conductors Insulators
Metals

Plastics

Graphite

Glass

 

Most other non-metals

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Leander

Author: Leander

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.