How to Calculate Thermal Conductivity to a Noise Temperature

Also known as Johnson-Nyquist noise, thermal noise is caused by the agitation of electrons inside a conductor, such as copper or aluminum electrical wire. Noise temperature is the resistance, measured in ohms, of the electrons as they travel along the conductor. Thermal conductivity is the rate at which heat transfers across a given material and is measured in degrees kelvin. The ratio of thermal conductivity to noise temperature is a concern; conductivity decreases as velocity increases, because the random movement of the electrons impede themselves from moving forward along the conductor.

Flat-head screwdriver
Phillips screwdriver
Multimeter
Probe thermometer
Paper
Pencil

Instructions

- 1
  Turn off the electrical supply energizing the conductor at the service panel or device switch, or unplug the power cord. Disconnect the wire terminals from the power supply with a flat-head or Phillips screwdriver if necessary.
- 2
  Set a multimeter to the “Ohm” setting. Touch either one of the meter’s two probes to one end of the conductor and the second meter probe to the opposite end of the conductor. Write down the reading of the multimeter.
- 3
  Place the tip of a probe thermometer on the surface of the conductor. Record the reading.
- 4
  Convert the Fahrenheit temperature to degrees kelvin. Subtract 32 from the conductor’s Fahrenheit temperature. For example, if the conductor’s temperature is 70 degrees Fahrenheit, the difference would equal 38 (70 minus 32 equals 38).
- 5
  Divide the difference by 1.8. With the 70-degree Fahrenheit example, the quotient would equal 21, rounded off (70 minus 32 equals 38, divided by 1.8 equals 21.11).
- 6
  Add 273.15 to the quotient to arrive at the conductor’s temperature in degrees kelvin. For example, an object with a temperature of 70 degrees Fahrenheit would have a temperature of 294.26 degrees kelvin (70 minus 32 equals 38, divided by 1.8 equals 21.11, plus 273.15 equals 294.26).
- 7
  Divide the temperature of the conductor in degrees kelvin by the conductor’s resistance in ohms to arrive at the conductivity to noise ratio. For example, a conductor with a resistance of 10 ohms and a temperature of 294.26 degrees kelvin would have a thermal conductivity to noise temperature ratio of 29-to-1 (294.26 divided by 10 equals 29.4).

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