Physics Keypoints: Vapours; This study material is suitable for students sitting for the following exams: JAMB, WAEC, NECO, GCE, IJMB, and JUPEB.
GAIN ADMISSION INTO ANY NIGERIAN UNIVERSITY WITHOUT JAMB – REGISTER FOR IJMB TODAY
Vapours play a crucial role in the Earth’s atmosphere, influencing various natural phenomena such as the formation of dew, mist, fog, and rain. In this comprehensive article, we will delve into the properties of saturated and unsaturated vapours, the relationship between saturated vapour pressure (S.V.P) and boiling, the determination of S.V.P using the barometer tube method, the formation of dew, mist, fog, and rain, and the study of dew point, humidity, and relative humidity.
Read other physics keypoints here
Additionally, we will explore hygrometry and the estimation of atmospheric humidity using wet and dry bulb hygrometers, concluding with detailed numerical problem-solving examples.
I. Saturated vs. Unsaturated Vapours
Understanding the distinction between saturated and unsaturated vapours is fundamental to grasping the behavior of gases and their interaction with liquids and solids.
Saturated Vapours: Saturated vapours are vapours in equilibrium with their liquid or solid phase at a specific temperature and pressure. When a vapour is saturated, it can no longer hold more of the substance in the gaseous state without undergoing condensation. The concept of saturation is vital in various meteorological and engineering applications.
Unsaturated Vapours: Unsaturated vapours are not in equilibrium with their liquid or solid phase at a given temperature and pressure. They have the potential to accommodate more of the substance in the gaseous state without causing condensation. Unsaturated vapours are prevalent in our everyday environment.
II. Saturated Vapour Pressure (S.V.P) and Boiling Point
Saturated vapour pressure (S.V.P) is the pressure exerted by a saturated vapour in equilibrium with its liquid or solid phase at a particular temperature. The relationship between S.V.P and boiling point is of great significance:
- Temperature and S.V.P: When the temperature of a substance increases, its S.V.P also increases. This means that at higher temperatures, more molecules of the substance transition into the vapour phase.
- Boiling Point: The boiling point of a substance is the temperature at which its S.V.P equals the atmospheric pressure. At this point, the substance changes from the liquid phase to the vapour phase. If the atmospheric pressure decreases, the boiling point also decreases, since the S.V.P required for boiling is reached at a lower temperature.
III. Determination of S.V.P by Barometer Tube Method
The barometer tube method is a technique used to measure the S.V.P of a liquid. This method provides valuable insights into the relationship between pressure and temperature for specific substances. To determine S.V.P using the barometer tube method:
- A glass tube with a known volume is partially filled with the liquid of interest.
- A vacuum is created above the liquid, ensuring no gas is present.
- The change in the height of the liquid column as it evaporates is measured.
- The ideal gas law is then applied to calculate the S.V.P.
IV. Formation of Dew, Mist, Fog, and Rain
Understanding the formation of these atmospheric phenomena is critical for meteorologists and anyone interested in weather patterns and conditions:
- Dew Formation: Dew forms when the temperature of the surroundings drops, causing the air to become saturated with moisture. This leads to condensation on cooler surfaces, such as grass and car windows, as the air’s S.V.P exceeds its capacity, resulting in the formation of water droplets.
- Mist and Fog: Mist and fog are akin to dew but occur in the air. Mist consists of tiny water droplets suspended in the air, while fog is denser. Both are formed when warm, moist air comes into contact with cooler air or surfaces, leading to condensation.
- Rain Formation: Raindrops are formed when water droplets in the clouds coalesce and become heavy enough to fall to the ground. This process is influenced by temperature, humidity, and atmospheric pressure, as well as the mechanisms of condensation and coalescence.
V. Dew Point, Humidity, and Relative Humidity
Dew point, humidity, and relative humidity are essential concepts for understanding the moisture content of the air:
- Dew Point: The dew point is the temperature at which air becomes saturated, leading to condensation. It provides valuable information about the likelihood of dew or frost formation and is essential for weather forecasts.
- Humidity: Humidity is a measure of the amount of moisture in the air. It can be expressed in various ways, such as specific humidity, mixing ratio, or absolute humidity.
- Relative Humidity: Relative humidity (RH) is the ratio of the current moisture content of the air to the maximum moisture it could hold at a given temperature. It is expressed as a percentage and is a key parameter in weather forecasting.
VI. Hygrometry and Estimation of Atmospheric Humidity
Hygrometry is the science of measuring humidity. Wet and dry bulb hygrometers are commonly used instruments for this purpose.
- Wet Bulb and Dry Bulb Temperatures: The wet bulb temperature is lower than the dry bulb temperature due to evaporative cooling. By measuring the temperature difference between the two, the relative humidity can be determined using psychrometric charts or equations.
- Psychrometric Charts: Psychrometric charts provide a graphical representation of the relationships between temperature, humidity, and pressure. They are invaluable tools for estimating various atmospheric properties and conditions.
VII. Numerical Problem-Solving
Solving numerical problems related to vapours, S.V.P, and humidity often involves using mathematical formulas and data to calculate specific parameters. Let’s delve into a few sample numerical problems with step-by-step solutions:
- Calculate the relative humidity when the wet bulb temperature is 20°C, and the dry bulb temperature is 25°C.
Solution: Use the psychrometric chart or relevant equations to calculate the relative humidity, considering the difference between wet and dry bulb temperatures.
- Determine the S.V.P of water at 25°C using the barometer tube method with the given data.
Solution: Apply the ideal gas law and relevant equations to calculate the S.V.P, incorporating the measurements and properties of the liquid.
In conclusion, the properties and behaviour of vapours have a profound impact on various fields, from meteorology to environmental science and engineering. The concepts presented in this article provide a robust foundation for further exploration of these phenomena and their practical applications in the real world.
