How to Calculate Capillary Rise in Water and Mercury

TL;DR

To calculate capillary rise in water, use the equation H = 2σsinθ/swr; for a glass tube with a 2mm diameter, capillary rise reaches 1.5 cm. In mercury, a higher contact angle leads to a capillary fall of approximately -0.49 cm. Surface tension, specific gravity, and radius are key factors influencing these results.

Transcript

hello friends in this video we are going to see the concept of capillary rise through a numerical so let's move on to video calculate the capillary rise in glass tube of 2mm daya when immersed in first water as well as secondly in mercury we know that there is capillary rise in water and capillary fall in case of mercury so we will see the numerica... Read More

Key Insights

• 😮 Capillary rise occurs when the contact angle is 0 degrees, resulting in a positive value for the height.
• 🥺 Capillary fall happens when the contact angle is greater than 0 degrees, leading to a negative height value.
• 😮 Surface tension and specific gravity play a significant role in determining the magnitude of capillary rise or fall.
• 😮 The equation H = 2σsinθ/swr provides a mathematical approach to calculate capillary rise or fall.
• 🤒 The values of surface tensions for water and mercury at 20 degrees Celsius are given as 0.0075 kg force per meter and 0.052 kg force per meter, respectively.
• 🤒 The conversion of surface tension from kg force per meter to kg force per centimeter is crucial for accurate calculations.
• 😮 Specific gravity, unit weight, and radius are other important factors in the capillary rise/fall equation.

Questions & Answers

Q: What is capillary rise and capillary fall?

Capillary rise is the upward movement of a liquid in a narrow tube due to surface tension, while capillary fall is the downward movement due to surface tension with some liquids.

Q: How can we calculate capillary rise or fall?

We can calculate it using the equation H = 2σsinθ/swr, where σ is surface tension, θ is the contact angle, s is specific gravity, w is unit weight, and r is the radius.

Q: Why is the contact angle necessary for the calculation?

The contact angle determines the inclination of the liquid at the interface between the liquid and the solid surface. It is crucial for calculating the capillary rise or fall.

Q: How is the contact angle different for water and mercury?

For water, the contact angle is generally considered as 0 degrees, while for mercury, it is often taken as 180 degrees or -1 in the equation.

Summary & Key Takeaways

• The video discusses the concept of capillary rise and fall in a glass tube when immersed in water and mercury.

• It provides the necessary surface tension properties and contact angles for both liquids.

• The video explains the mathematical equation used to calculate the capillary rise or fall.