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To convert a delta temperature from degrees Fahrenheit to degrees Celsius, the formula is {ΔT} °F = 9 / 5 {ΔT} °C. To convert a delta temperature from degrees Celsius to kelvin, it is 1:1 ({ΔT} °C = {ΔT} K).
When converting a temperature interval between the Fahrenheit and Celsius scales, only the ratio is used, without any constant (in this case, the interval has the same numeric value in kelvins as in degrees Celsius): f °F to c °C or k K: c = k = f / 1.8 c °C or k K to f °F: f = c × 1.8 = k × 1.8
Reversing this yields the formula for obtaining a quantity in units of Celsius from units of Fahrenheit; one could have started with the equivalence between 100 °C and 212 °F, which yields the same formula. Hence, to convert the numerical quantity value of a temperature T[F] in degrees Fahrenheit to a numerical quantity value T[C] in degrees ...
This definition also precisely related the Celsius scale to the Kelvin scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 °C. Until 19 May 2019, the temperature of the triple point of water was defined as exactly 273.16 ...
Anders Celsius's original thermometer used a reversed scale, with 100 as the freezing point and 0 as the boiling point of water.. In 1742, Swedish astronomer Anders Celsius (1701–1744) created a temperature scale that was the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water. [5]
That same year, James Prescott Joule suggested to Thomson that the true formula for Carnot's function was [20] = +, where is "the mechanical equivalent of a unit of heat", [21] now referred to as the specific heat capacity of water, approximately 771.8 foot-pounds force per degree Fahrenheit per pound (4,153 J/K/kg). [22]
Similar to the Kelvin scale, which was first proposed in 1848, [1] zero on the Rankine scale is absolute zero, but a temperature difference of one Rankine degree (°R or °Ra) is defined as equal to one Fahrenheit degree, rather than the Celsius degree used on the Kelvin scale.
Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 bar (100 kPa, 10 5 Pa). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). [3] This standard is also called normal temperature and pressure (abbreviated as NTP).