Question

Why is the total thermal resistance calculated in an opposite way to that of electric resistance?

Answer 1

I do not understand why you are saying it is not.
The analogy between thermal and electrical resistance is valid:
Temperature --> electric potential
Difference in temperature --> potential difference
Thermal flux (power) --> current
Thermal conductivity--> electric conductivity

Hence:

\(T_1-T_2=R_{th}\Phi\)
\(V_1-V_2=R_{el}\;I\)
with
\(R_{th}=\dfrac{l}{\lambda S}\) ; \(R_{el}=\dfrac{l}{\gamma S}\)
\(\lambda\) : thermal conductivity
\(\gamma\) : electric conductivity

Answer 2

Maybe its a mistake in the lecture i am studying from thanks...
so if i have a slab where there is a temperature difference at the ends of the sides of the slab. particles in the slab tend to vibrate with greater amplitudes colliding with the nearby particles transfer some of their energy during the collision. Are electrons responsible for that heat flow? second point i noticed in the lecture is that Delta T is not equal to the final temperature-initial temperature?

Answer 3

Probably \(\Delta T=T_1-T_2\) is the temprerature difference between either sides of the slab.

Careful: the thermal resistance concept only holds in steady state problems. So does the electrical resistance, but the time constants for these phenomena are very different.
Steady-state in electricity is reached in a matter of \(10^{-19}\)s, whereas it can take hours or days to reach a steady state in thermal conductivity.