Resistivity

Resistvity is the total resistance of a material

Equation for calculating resistance

If we know the:

• area of the cross-section of the wire
• length of the wire
• resistivity of the material

we can calculate the resistance of the wire using the equation:

where:

• is the resistance (in ohms, )
• is the resistivity of the material (in ohm metres, )
• is the length of the wire (in metres, m)
• is the area of the cross-section of the wire (in square metres, )

The resistivity of copper is . Calculate the resistance of a copper wire of length and cross-sectional area of

• R=
• Answer:

Two of these wires are used to connect a lamp to a power supply of negligible internal resistance. The p.d. across the lamp is and its power is . Calculate the potential difference across each wire.

• Power,
• Rearranging for :
• Each wire has resistance of
• Total resistance of wires =
• Total resistance in circuit = resistance of lamp
• Using to find current,
• Potential difference across each wire,
• Answer: across each wire

What length of copper wire of diameter 0.1mm is required to make a coil with resistance ? (Resistivity of copper = )

• Rearranging for :
• Answer:

If the resistivity of copper is calculate the resistance of of copper, when in the form of a wire of diameter

• Answer: