Q1: A thermally thin body is the one for which

ANS:A - Biot number is less than 0.1.

A thermally thin body is characterized by a Fourier number (Fo) that is less than 0.1. Explanation:

1. Definition of Fourier Number (Fo):
   • The Fourier number (Fo) is a dimensionless parameter used in heat transfer analysis to describe the ratio of the rate of heat conduction to the rate of thermal energy storage in a medium.
   • It is defined as the ratio of the time taken for heat conduction to penetrate a certain distance into a material to the characteristic time scale for thermal energy to diffuse through the material.
   • Mathematically, it is expressed as: Fo=L2αt​ where:
     • α is the thermal diffusivity of the material.
     • t is the time elapsed.
     • L is the characteristic length scale of the body.
2. Interpretation:
   • A Fourier number less than 0.1 indicates that the time required for heat conduction to penetrate a certain distance is much shorter than the time required for thermal energy to diffuse through the material.
   • In other words, it implies that the body responds quickly to changes in temperature, and heat conduction dominates over thermal energy storage.
   • This condition is typically observed in bodies with low thermal inertia or those with high thermal conductivity and/or thin dimensions.
3. Thermally Thin Body:
   • A thermally thin body is one that responds rapidly to changes in temperature and exhibits fast heat transfer characteristics.
   • Such bodies have relatively low thermal inertia and tend to reach thermal equilibrium quickly.
   • A Fourier number less than 0.1 indicates that the body is thermally thin, as it implies that heat conduction occurs much faster compared to the rate of thermal energy storage.