 # To Determine the Surface Tension of Water by Capillary Rise Method - Physics Practical Class 11 Viva Questions with Answers

1. What is surface tension?
2. Answer. Surface tension is defined as the tension of the surface film of a liquid caused due to the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimise surface area.

3. How is surface tension measured?
4. Answer. The surface tension is measured in dynes/cm.

5. What causes insects to float on water?
6. Answer. Surface tension allows objects of more density than water, like insects, to float.

7. What is the formula to calculate the surface tension of water?
8. Answer. The surface tension of water can be calculated using the formula:

$$\begin{array}{l}T=\frac{r(r+h/3)\rho g}{2cos\Theta}\end{array}$$

9. What happens to surface tension when the temperature increases?
10. Answer. The surface tension decreases when the temperature increases since the net attraction force among molecules are reduced.

11. What is the surface tension of water?
12. Answer. The surface tension of water is 0.072 N/m.

13. What is the CGS unit of surface tension?
14. Answer. The CGS unit of surface tension is dyn/cm.

15. Give an example where we can witness surface tension.
16. Answer. Insects walking on water and the shape of liquid droplets are ideal examples of surface tension.

17. Can the surface tension of water support a razor blade?
18. Answer. Yes, a razor blade can be supported by the surface tension of water since the razorblade is of higher density than water.

19. Which are the various types of forces due to which the liquid rises?
20. Answer. Forces responsible for the liquid rise are

• Cohesion
• Surface tension
21. What would be the shape of the meniscus when the contact angle is greater than 90 degrees?
22. Answer. The shape of the meniscus when the contact angle is greater than 90 degrees would be convex.

23. Define cohesion.
24. Answer: Cohesion is defined as the intermolecular attraction that acts between two same kinds of molecules.