9.7 Resistance and resistivity

Question 1

What is the relationship between resistance and length of a wire?

Answer 1

Resistance is directly proportional to the length of a wire.
R∝L

Question 2

What is the relationship between resistance and the cross-sectional area of a wire?

Answer 2

Resistance is inversely proportional to the cross-sectional area of a wire.
R∝1/A

Question 3

What is resistivity?

Answer 3

The measure of how much a particular material opposes electron flow.

Question 4

What is the equation for resistivity?

Answer 4

resistivity = (resistance x cross-sectional area)/ length
ρ= (RA)/L unit: Ωm
∴R=(ρL)/A

Question 5

What order of 10 do most materials have?

Answer 5

Good conductors such as metals have a resistivity of x10^-8 Ωm whereas insulators hav x10^16 Ωm. Semiconductors have a resistivity in between this range.

Question 6

How do impurites affect semiconductors?

Answer 6

Impurities in semiconductors such as silicon significantly increase conduction.

Question 7

What is superconductivity?

Answer 7

When some materials are cooled, their resistivity drops but at critical temperatures, the resistivity suddenly drops to zero.