Which law would you use to relate the flow rate of a liquid through a narrow tube?

• A. Bernoulli's law
• B. Poiseuille's law
• C. Snell's law
• D. Doppler's law

Answer: (B)

Poiseuille's law is the appropriate choice for relating the flow rate of a liquid through a narrow tube. This law specifically describes how the flow of a viscous fluid through a cylindrical pipe is affected by factors such as the radius of the tube, the pressure difference across the length of the tube, and the viscosity of the fluid. It provides a mathematical relationship that defines how much fluid will flow per unit of time based on these parameters, allowing for precise calculations in fluid dynamics.

In contexts where fluid behavior in tubes is analyzed, such as medical applications or engineering scenarios involving pipes and pumps, Poiseuille's law effectively indicates that flow rate is directly proportional to the fourth power of the radius of the tube and directly proportional to the pressure gradient, while being inversely proportional to the fluid's viscosity. This foundational understanding is crucial for predicting how various liquids will behave when forced through small openings or narrow conduits.

While Bernoulli's law deals with the relationship between pressure and velocity in a flowing fluid, it does not specifically address viscous flow in a narrow tube. Snell's law is related to the refraction of light, and Doppler's law pertains to the change in frequency or wavelength of waves in relation to an observer moving relative to