Which of the following laws pertains to the flow of viscous fluids?

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

Answer: (B)

Poiseuille's law specifically addresses the flow of viscous fluids, particularly in the context of laminar flow through a cylindrical pipe. This law quantifies the relationship between the pressure difference across the length of the pipe, the viscosity of the fluid, the length of the pipe, and its radius. According to Poiseuille's law, the flow rate of a fluid is directly proportional to the fourth power of the radius of the pipe and the pressure difference, and inversely proportional to the viscosity and the length of the pipe. This relationship is crucial for understanding how fluids behave under different conditions, particularly in medical applications such as blood flow in vessels or in engineering contexts involving fluid transport.

In contrast, other laws mentioned in the options serve different purposes. Bernoulli's law deals with the conservation of energy in fluid flow, often applied to streamline flows and relating pressure, velocity, and height. Snell's law is fundamentally about the refraction of light waves as they pass from one medium to another. Doppler's law describes the change in frequency or wavelength of waves in relation to an observer moving relative to the source of the waves. These laws do not specifically address the mechanics of viscous fluid flow like Poiseuille's law does.