Under which of the following conditions stated with respect to in
A. When internal resistance is more than 10% of external resistance
B. When internal resistance is equal to external resistance
C. When internal resistance is less than 10% of external resistance
D. When internal resistance is equal to 10% of external resistance.
Please scroll down to see the correct answer and solution guide.
Right Answer is: C
SOLUTION
Concept:
Lumped system analysis is determined by a parameter known as Biot number which is given as,
\(Bi = \frac{{hL}}{k}\)
where h = convective heat transfer coefficient
k = coefficient of thermal conductivity
L = characteristic length of the body equal to volume upon the area.
Also,
Convective resistance = \(\frac{{1}}{{hA}}\)
Conductive resistance = \(\frac{{L}}{{kA}}\)
If the Biot number is less than 0.1 then we use lumped system analysis.
Biot number can also be written as,
\(\frac{{Internal\;conductive\;resistance}}{{External\;convective\;resitance\;}} = \frac{{hL}}{{k}}\) = Bi
Therefore, option C is correct.