Final answer:
In physics, a water gauge glass located 7 feet or higher from the operating floor must have a visible indication of its position, either on or off. This ensures that operators can easily determine the liquid level without having to physically check the glass.
Step-by-step explanation:
In physics, a water gauge glass is commonly used to measure the liquid level in a tank or boiler. According to the question, a water gauge glass located 7 feet or higher from the operating floor must have a visible indication of its position, either on or off. This ensures that operators can easily determine the liquid level without having to physically check the glass.
For example, if the water gauge glass is located at a height of 7 feet, a bright light source and a small bright object (such as a silver spoon) can be used. When the liquid level is below the glass, the bright object can be placed behind the glass to create a visible indication that the glass is off. Conversely, when the liquid level reaches the glass, the bright object can be removed, indicating that the glass is on. This visible indication helps in monitoring and maintaining appropriate liquid levels in various systems.
Therefore, to ensure safety and efficiency, it is important for a water gauge glass located 7 feet or more from the operating floor to have a visible indication of its position, be it on or off.