A student constructs a model depth-gauge to measure hydrostatic pressure at different depths in a water tank, as shown in the diagram below:
Explain, in terms of particles, how the trapped air inside the rigid container exerts a pressure on the silicone membrane.
Initially, the container is at the surface of the water, the silicone membrane is flat, and the indicator needle is horizontal. The student lowers the gauge deep into a freshwater tank. Explain what happens to the different parts of the gauge as the depth increases. (Assume the temperature of the air inside the container remains constant.)
Suggest two design modifications that could be made to this gauge to increase its sensitivity to changes in depth.
The student now leaves the gauge at a fixed depth but pours hot water into the tank, heating the air inside the container.
State how this heating affects the position of the free end of the indicator needle.
Using ideas about particles, explain why this change occurs.
