Text: # Convert Celsius to Kelvin: K = °C + 273 # Convert Celsius to Fahrenheit: °F = 1.8(°C) + 32 THE KELVIN SCALE OF TEMPERATURE Since it is inconvenient to use the negative values when measuring low temperatures of either the Fahrenheit or the Celsius scales, in the nineteenth century, Lord Kelvin, an Englishman, invented an new temperature scale suitable for measuring low temperatures. When a material is cooled, it looses heat, and its temperature decreases, until a point is reached where it has no more heat left to loose. At this point it is not possible to lower the temperature any further. This low temperature is called absolute zero. Lord Kelvin suggested that this absolute zero temperature be the basis of a new scale which begins with the value zero at absolute zero. At sea level on this scale, water freezes at 273 degrees, and boils at 373 degrees. So, just like the Celsius scale, there is a difference of 100 degrees between the freezing and boiling points of water. This new scale is called the Kelvin scale in honor of Lord Kelvin, and has the unit "Kelvin". To convert from degrees "Celsius" to degrees "Kelvin" use the formula: Kelvin = degrees Celsius + 273 This scale is very convenient for recording the very low temperatures of liquid nitrogen and liquid helium. On this scale, nitrogen condenses to a liquid at 77 Kelvin, and helium, a chilly 4.2 Kelvin. YBa2Cu3O7 has a Critical Temperature of about 90 Kelvin, and BiSrCaCu2O9 a Critical Temperature of 110 Kelvin. Thus when they are immersed in liquid nitrogen at 77 Kelvin, they become superconducting. ----------------- Kelvin Scale The Kelvin temperature scale (K) was developed by Lord Kelvin in the mid 1800s. The zero point on this scale is base on the point at which the pressure of all dilute gases mathematically project to zero from the triple point of water The triple point of water occurs at 0.01 °C (273.16 K or 32.02 °F). Recall that the triple point is the temperature at which liquid water, ice, and water vapor can coexist simultaneously. The zero point of this scale is equivalent to -273.16 °C on the Celsius scale. This zero point is considered the lowest possible temperature of anything in the universe. Therefore, the Kelvin scale is also known as the "absolute temperature scale". At the freezing point of water, the temperature of the Kelvin scale reads 273 K. At the boiling point of water, it reads 373 K. Lord Kelvin developed this scale with the help of a Carnot engine. The Carnot engine deals with the relationship between pressure, work, and temperature. The Carnot engine is the most efficient engine possible. However, even it cannot reach 100% efficiency. If an engine was 100% efficient, no energy would be wasted. The Carnot engine is only theoretical, which means that all real engines are even less efficient. To learn more about Carnot engines, go to your local library and look for books on the fundamentals of physics or thermodynamics. A selection of Kelvin temperatures Absolute zero 0.00 K Cosmic background radiation 2.73 K Freezing point of hydrogen 13.97 K Boiling point of hydrogen 20.41 K Surface of Pluto (mean) 53 K Freezing point of water 273.16 K Surface of the Earth (mean) 288 K Boiling point of water 373.16 K Surface of Mercury (mean) 445 K Freezing point of iron 1,811 K Boiling point of iron 3,110 K Surface of a red (M-type) Star 50,000 K

See Also: RANKINE SCALE OF TEMPERATURE

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