A clean glass capillary tube is held vertically in water raised to a height of 7cm. The tube is down depressed and only 5cm of its length is above water. What will be the angle of contact?
To determine the angle of contact, we need to consider the phenomenon of capillarity. Capillarity occurs when a liquid rises or falls in a narrow tube due to the combination of adhesive and cohesive forces.
In this scenario, the glass capillary tube is held vertically in water, and the water rises to a height of 7 cm. When the tube is depressed, only 5 cm of its length remains above water.
The angle of contact, denoted as θ, is the angle between the liquid (water) and the solid (glass) at the point where they meet. It depends on the relative strengths of adhesive and cohesive forces.
To find the angle of contact, we can use the equation:
cos θ = (h2 - h1) / L
where h2 is the rise of liquid when the tube is depressed (7 cm), h1 is the initial rise of liquid in the tube (5 cm), and L is the length of the exposed portion of the tube (5 cm).
Plugging in the values into the equation, we get:
cos θ = (7 - 5) / 5
cos θ = 2 / 5
θ ≈ 65.9 degrees
Therefore, the angle of contact in this scenario is approximately 65.9 degrees.