1. What is the Magnus Formula?

The Magnus formula is an empirical relationship that calculates the vapour pressure of pure water over liquid water. It provides an accurate estimation of saturation vapour pressure based on temperature.

2. How Does the Calculator Work?

The calculator uses the Magnus formula:

Where:

• \( e_s \) — Saturation vapour pressure (hPa)
• \( T \) — Temperature (°C)
• 6.112 — Reference vapour pressure at 0°C (hPa)
• 17.67 and 243.5 — Empirical constants

Explanation: The formula describes how vapour pressure increases exponentially with temperature, following the Clausius-Clapeyron relation.

3. Importance of Vapour Pressure Calculation

Details: Accurate vapour pressure calculation is crucial for meteorological forecasting, humidity measurement, climate studies, and various industrial processes involving water vapor.

4. Using the Calculator

Tips: Enter temperature in degrees Celsius. The calculator will compute the saturation vapour pressure in hectopascals (hPa).

5. Frequently Asked Questions (FAQ)

Q1: What is the range of validity for the Magnus formula?
A: The formula is valid for temperatures between -45°C to 60°C for water vapor over liquid water.

Q2: How does vapour pressure relate to relative humidity?
A: Relative humidity = (actual vapour pressure / saturation vapour pressure) × 100%

Q3: Why does vapour pressure increase with temperature?
A: Higher temperatures provide more kinetic energy for water molecules to escape from the liquid phase into the vapor phase.

Q4: Are there alternative formulas for vapour pressure calculation?
A: Yes, other formulas include the Goff-Gratch equation, Buck equation, and Tetens formula, each with slightly different coefficients and ranges of validity.

Q5: What are typical vapour pressure values?
A: At 0°C: 6.11 hPa, at 20°C: 23.39 hPa, at 40°C: 73.78 hPa. The values approximately double for every 10°C temperature increase.