Metals, Semiconductors and Insulators

Question 1

what is the equation for current when working out the conductivity of a material

Answer 1

I = nAvq

Question 2

what could the charge, q be for a group 1 and 2 element

Answer 2

• it is usually the electron charge of a single electron, e
• but for a doubly charged ion from group 2 it can be 2e
• as you have 2 delocalised electrons per atom (ion)

Question 3

what is different about A compared to the other variables in this equation

Answer 3

• it is not a property of the material itself
• being the cross sectional area, it can change depending on how thick the wire of the material is
• which is artificially done by us

Question 4

why is n so important in this equation

Answer 4

• n is the number of charge carriers per cubic meter

- this is the only variable that really determines the ability of a given material to conduct an electric current

Question 5

what is the range for n in metals

Answer 5

10^28 m^-3 to 10^29 m^-3

Question 6

what is the value of n for insulator such as glass or polystyrene

Answer 6

they virtually have no charge carriers at room temperature

Question 7

what is the range for n in semiconductors

Answer 7

• 10^17 m^-3 (silicon)

- to 10^19 m^-3 (germanium)

Question 8

what implication can you draw from comparing the number of charge carriers between metals and semiconductors

Answer 8

metals are much better at conducting than semiconductors

Question 9

how can the ability of semiconductors to conduct be increased

Answer 9

• by increasing the temperature

- or adding impurity atoms