AS AQA Phys Unit 1- Resistivity and Superconductivity

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Resistivity

The resistance of a component, such as a length of wire, depends upon three measurements;

1) Length (l); the longer the wire, the more difficult it is for current to flow.

2) Area (A); the wider the wire, the easier it is for electrons to pass through.

3) Resistivity (p); depends on the material. The structure may make it easy or difficult for charge to flow. In general, resistivity depends on environmental factors as well e.g. temperature and light intensity.

The resistivity of a material is defined as the resistance of a 1m length with a 1m^2 cross-sectional area. It is measured in ohm-metres.

p = R A / l

where p is the symbol rho for resistivity, R is the resistance, A is cross-sectional area in m^2 and l = length in m

The equation is usually seen in the form;

R = p * l / A

Typical resistivity values of conductors are very small e.g. copper at 25 degrees C = 1.72*10^-8 ohmic…

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