Worksheet: Contact Angles
In this worksheet, we will practice relating the contact angles of drops on a surface with the solid–liquid, liquid–gas, and solid–gas surface tensions.
How is it possible for a steel needle to be supported on the surface of water?
- AThe interactions between water molecules are stronger than those between water and steel, so the system has a lower potential energy if the needle does not sink.
- BSteel is less dense than water.
- CSinking of the needle is energetically costly because air–water interactions are much weaker than air–steel interactions.
- DThe high surface tension of water supports the steel needle.
- ESinking of the needle is energetically costly because it increases the surface area of the water per unit volume.
When a glass capillary tube is placed into a flask of mercury, the meniscus of the mercury in the tube is lower than the surface of the mercury outside. What can be concluded from this observation?
- AThe contact angle between mercury and glass is less than .
- BThe contact angle between mercury and glass is negative.
- CThe surface tension between mercury and glass is zero.
- DThe contact angle between mercury and glass is greater than .
- EThe surface tension between mercury and glass is negative.