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WEEK 6
ELECTRIC MEASUREMENT
CONTENT
- Resistivity and conductivity
- Conversion of galvanometer to ammeter and voltmeter
- Measuring resistance ammeter- voltmeter method.
RESISTIVITY AND CONDUCTIVITY
The resistance of a wire maintain at a constant temperature is related to its length L and its cross-sectional area (A) by the expression
R = ρl/A
Where ρ is a constant known as resistivity of the material (its unit is ohm-metre, Ωm)
ρ = RA/l
R = resistance, A = cross-sectional area, l = length of the wire.
The resistance is the ability of a material to oppose the flow of current through it. The greater the resistivity of a wire the poorer it is as an electrical conductor. That is why conductivity is used to specify the current –carrying ability of a material. The greater the conductivity of a material, the more easily can current flow through the material. Hence, materials with high conductivity will have low resistively.
Conductivity, σ is the reciprocal of the resistivity
σ = 1/ρ
Electrical Conductivity: This is a measure of the extent to which a material will allow current to flow easily through it when a p.d is applied at a specified temperature. It is the reciprocal of the resistivity.
GALVANOMETER CONVERSION
Conversion of galvanometer to ammeter (Shunt)
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