🔍 Key Concepts

• bi-color water level gauge construction (two colored light sources shining through the water column) • physical differences between steam vs. water inside a boiler drum • optical properties: how light passes through one medium vs. another

💭 Think About

• If the gauge is connected directly to the drum and uses no added fluids, what physical difference between steam and water can an instrument use continuously and safely? • Ask yourself why the gauge shows two different colors at the water portion and the steam portion of the glass—what property of the two media is being exploited? • Which option describes something that can be used instantly and visually, without waiting for a reaction or change in pressure?

✅ Before You Answer

• Confirm that no extra chemical or special indicating fluid is normally added to a boiler water level gauge. • Think about whether pressure is actually different in the steam space and water space of the same drum, or essentially the same. • Focus on a property that would make a visual color change at the interface between water and steam possible.