Investigating Conductors & Insulators (Cambridge (CIE) O Level Physics): Revision Note

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

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

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

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