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Name: Jessica
Status: Student
Grade: 9-12
Location: OH
Country: United States
Date: January 2007


Question:
How do you test the electrical conductivity in metals?



Replies:
Hi Jessica

Conductivity can be inferred by measuring the resistance. If you hook up a sample to be tested to a voltage source and measure the current going through the sample and the voltage across the sample, the resistance can be calculated from Ohm's law: R = E/I where R is resistance in ohms, E is voltage in volts and I is current in amperes. Once you have resistance, you can calculate resistivity. Resistivity is a factor, which when multiplied by the length of the sample and divided by its cross-sectional area, will yield the resistance. Conductivity is the reciprocal of the resistivity. The higher the conductivity, the easier it is to pass a current through the material.

Hope this helps.

Bob Froehlich


Hi Jessica,

Electrical resistance is tested with an Ohmmeter. This is a simple device that sends a measured current through a sample of the metal in question, and measures the voltage required to "push" this current through the metal. Ohm's Law states that the resistance (in Ohms) of a conductor is equal to the voltage (in Volts) required to drive a resulting current (in Amperes). To give an example, let us say that you have a sample of a long thin metal wire. You attach electrical contacts to each end and apply a voltage of (let us say) 1 Volt between each end of the wire. This 1 Volt difference from one end of the wire to the other, causes a current to flow down the wire. If the resulting current was 1 Ampere, then the resistance of the wire is 1 Ohm. If only 0.5 Ampere had resulted, then the wire's resistance would be 1 Volt divided by 0.5 Ampere, or 2 Ohms.

Regards,

Bob Wilson



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