What governs the heating capacity of a muffle furnace? For a given firing condition, the practical heating capacity of a muffle furnace depends primarily on which set of factors?

Introduction / Context:
In muffle furnaces, the load (stock) is heated primarily by radiation from the hot muffle walls and by convection within the enclosed chamber. The rate at which energy reaches the stock determines the effective heating capacity.

Given Data / Assumptions:

• Radiative heat transfer dominates at high temperatures.
• Emissivity and area govern radiative exchange.

Concept / Approach:
Net radiative exchange between a hot wall and the stock depends on both the wall’s radiative properties and the stock’s absorptivity/emissivity and view factors. Larger area and higher emissivity support greater radiative heat flux; higher wall temperature increases driving potential strongly.

Step-by-Step Solution:

Verification / Alternative check:
Standard furnace design notes highlight that blackened or high-emissivity stock surfaces heat faster, and high-emissivity, large-area hot walls deliver greater radiant energy.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring emissivity; bright or oxidized surfaces can change heating rates markedly even at the same gas or wall temperature.

Final Answer:
both (a) & (b)