Johnson Noise Thermometry - Page 12



Let’s see this in operation. Here is how we make a Johnson noise thermometer. Essentially all we have to do is connected any resistance sensor to a true RMS voltmeter. The material of the sensor is unimportant. The resistor is show in blue to indicate that it is cold but the meter does not read zero sine it is not an absolute zero and Is therefore generating some Johnson noise. The Johnson noise is white, which means that it has the same power density at all frequencies and our voltmeter will respond to frequencies in its operating bandwidth. As we heat the resistor the meter will indicate progressively higher readings as the electrons that within the resistor are excited into high energy states. The system is measuring the electrical noise generate by the thermally excited electrons in the resistor and as they get hotter their average speed increases thereby increasing the noise generated. The noise is directly related to the temperature of the electrons generating the noise.


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