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Thermal Physics

Cool goIITian

Joined:	24 Jun 2007
Post:	61

28 Jan 2008 12:41:32 IST

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359

Electricity in Thermodynamics

None

are the kirchoffs laws and wheatstone bridge hat we use in electricity applicable in solving problems of conduction i.e. heat current. An example is :-

A system of rods each of length l & cross sectional area S are assembled. Mode of heat transfer is conduction and the system is in steady state. The temperature at junction A is t and that of C is 2T. Find temperature of junction of B & D and rate of heat flow along BD.

(Figure is attached)

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Comments (2)

Anshuman Johri

Blazing goIITian

Joined: 27 Jan 2007

Posts: 559

28 Jan 2008 13:33:43 IST

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I have a bad experience of solving such problems by converting such figures into corresponding electrical circuits... so i suggest not to use electrical circuit combinations...

this one is from full test IV AITS

use the formula H = kS(T - T₀)/L

now for this problem consider the figure

so

At D

H1 = H2 + H3

put the values of H1, H2 and H3
u'll get

4T₁ - T₂ = 4T .....(1)

At B

H5 = H3 + H4
put the values og H3,H4,H5

u'll get

3T₁ -2T₂ = T .......(2)

solve the equations 1 and 2

so temp of D = 1.4 T
and temp of B = 1.6 T

now heat flow along BD = H3= kS(1.6T - 1.4T)/L = kST/5L

Bipin Dubey

Forum Expert

Joined: 23 Jan 2007

Posts: 7942

28 Jan 2008 16:20:47 IST

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Well done Anshuman. That was a perfect solution.

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