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• The three factors that resistance depends on.

• The value you got for your gradient.

• The value you worked out for the resistivity (Gradient x Area).

Resistivity

Resistivity Equation

Units

• R is measured in Ω

• ρ is measured in Ωm

• G is measured in S (Siemens)

• σ is measured in Sm-1

Temperature and Resistance in Metals

As temperature increases the resistance within metals increases.

This is because as the temperature increases, the lattice begins to vibrate scattering the free electrons in the metal.

This increases resistance.

Temperature and Resistance in Semi-Conductors

As temperature increases the resistance within semi-conductors decreases.

This is because as the temperature increases, more electrons are freed to move around.

This decreases resistance.

Work out the Error

• I measure the radius of a wire to be 0.0002±0.00005m

• I measure the length to be 0.10±0.005m

• What is the percentage error in my cross-sectional area?

• What is the percentage error in my value of resistance, assuming there are no other errors?