The question on the screen is: **"The Prandtl number is greater than 1 for a fluid which is flowing over a flat plate, how is the variation of thermal boundary layer with respect to hydrodynamic boundary layer for a laminar flow?"** The options are: 1. Thinner than the hydrodynamic boundary layer 2. Of same thickness as that of hydrodynamic boundary layer 3. Thicker than the hydrodynamic layer 4. Data is insufficient to answer ### **Answer:** When the **Prandtl number (Pr) > 1**, the **thermal boundary layer** is **thinner** than the **hydrodynamic boundary layer** for a laminar flow over a flat plate. #### **Correct Option:** **Thinner than the hydrodynamic boundary layer** #### **Explanation:** - **Prandtl number (Pr) = ν/α = kinematic viscosity / thermal diffusivity** - If Pr > 1, the momentum diffusivity is greater than thermal diffusivity, so the velocity boundary layer grows faster than the thermal boundary layer. - Therefore, the thermal boundary layer is thinner. If you need further explanation, feel free to ask!