Final answer:
Fluid levels in an open-tube manometer equalize because atmospheric pressure acts equally on open ends. The diameter of the tubes does not affect the fluid equilibrium, as pressure is determined by the height of the fluid column alone. The correct option in this case is (b) Atmospheric pressure acts equally on both sides.
Step-by-step explanation:
The fluid in a manometer reaches equal levels on either side when both sides are open to the atmosphere because atmospheric pressure acts equally on both sides. The diameter of the tubes does not affect this equilibrium because fluid pressure at a particular depth is dependent only on the height of the fluid and not on the shape of the container. This is explained by the principle that pressure due to the weight of a fluid is given by P = hρg, where h is the height of the fluid, ρ is the fluid density, and g is the acceleration due to gravity. When the fluid levels are unequal, there is greater pressure on the deeper side, causing the fluid to flow until the levels equalize. This behavior adheres to basic principles of physics and does not rely on factors such as fluid viscosity or the conservation of mass in this context.
To address the specific options given in the question:
- The law of conservation of mass is not directly related to fluid levels in a manometer.
- Atmospheric pressure acting equally on both sides is the main reason for the fluid levels being equal.
- Fluid viscosity does not compensate for the diameter difference in this scenario.
- While gravitational force does impact the fluid levels, it is not the reason they equalize in this case.
The correct option in this case is (b) Atmospheric pressure acts equally on both sides.