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Assertion             :       The equivalent thermal conductivity of two plates of same thickness in contact (series) is less than the smaller value of thermal conductivity.            Reason                 :       For two plates of equal thickness in contact (series) the equivalent thermal conductivity is given by       [AIIMS 1997] \[\frac{1}{K}=\frac{1}{{{K}_{1}}}+\frac{1}{{{K}_{2}}}\]

A)             If both assertion and reason are true and the reason is the correct explanation of the assertion.

B)             If both assertion and reason are true but reason is not the correct explanation of the assertion.

C)             If assertion is true but reason is false.

D)             If the assertion and reason both are false.

E)             If assertion is false but reason is true.

Correct Answer: D

Solution :

                   Equivalent thermal conductivity of two equally thick plates in series combination is given by                           \[\frac{2}{K}=\frac{1}{{{K}_{1}}}+\frac{1}{{{K}_{2}}}\]                    If \[{{K}_{1}}<{{K}_{2}}\]             then \[{{K}_{1}}<K<{{K}_{2}}\] Hence assertion and reason both are false.