Vrms stands for root mean square velocity and it is a measure of the average speed of particles in a gas. In the case of helium, Vrms is used to calculate the average speed of helium atoms at a given temperature.
The formula for calculating Vrms for a gas is √(3RT/M), where R is the gas constant, T is the temperature in Kelvin, and M is the molar mass of the gas. For helium at 5K, the calculation would be √(3 * 8.314 J/molK * 5K / 4.003 g/mol) = 920 m/s.
5K is a significant temperature because it is the boiling point of helium. At this temperature, helium transitions from a gas to a liquid, and the average speed of the helium atoms decreases significantly. This makes it a useful temperature to study the properties of helium at its critical point.
Helium has the lowest molar mass of any gas, which means it has the highest Vrms at any given temperature. At 5K, the Vrms of helium is about 920 m/s, while the Vrms of other gases at the same temperature can range from 500-700 m/s.
Calculating Vrms at 5K for helium is important in understanding the behavior of helium at low temperatures, which has many practical applications. It is used in cryogenics for cooling materials to very low temperatures, and in superconductivity research where helium is used as a coolant. It is also used in the study of phase transitions and critical phenomena in gases.