Resistivity - Cost
General Information
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This chart is important for designing components requiring good electrical insulation (e.g.
plug casings) or good electrical conductivity (e.g. electric power cables) at a good price
Good electrical conductors are usually good thermal conductors and good electrical
insulators are good thermal insulators
The similarity between electrical and thermal properties means that the chart can also be
used to identify materials requiring good thermal insulation (e.g. for kiln walls) or thermal
conductivity (e.g. for frying pans)
Physical Insights
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Metals are much better conductors than other materials because they have metallic bonds in
which valence electrons are pooled. These electrons are free to move and carry current
Pure metals are much better conductors than alloys - this is because electrons travelling
through the material are obstructed by irregularities such as alloying atoms
Polymers and ceramics are good insulators because they are covalently bonded and so their
electrons are all tightly bound
Semiconductors are ‘doped’ with elements which provide extra electrons (n-type) or provide
positive holes (p-type) which can move freely
Resistivity - Cost
Example Uses
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Gold and silver have the best conductivities but are too expensive to be widely used, except
as connectors in electronic applications
In general the next best materials, copper and aluminium, are used (e.g. electric cables)
Polymers like urea formaldehyde are insulators, and are used in electrical components to
protect the user (e.g. light switch casings)
Simple Questions
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Why is copper used instead of brass for electric cables?
Why do metals feel cold to touch?
Select materials for an electric drill body.
Select materials for the main body of a 13A fuse.
Select materials for a cavity wall or attic insulation.
Further Questions
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If polymers are bad insulators why do trees get struck by lightning?
Why must silicon used in semiconductors be really pure?
Why do electronic components get hot?
Metals and alloys
Ceramics
Polymers
Wood and wood products
Composites
Select chart:
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Young's modulus - Density
Young's Modulus - Cost
Strength - Density
Strength - Toughness
Strength - Elongation
Strength - Cost
Strength - Max service temperature
Specific stiffness - Specific strength
Electrical resistivity - Cost
Recycle Fraction - Cost
Energy content - Cost