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Standard XII

Physics

Emissive and Absorptive Power

Three conduct...

Question

Three conducting rods of same material and cross-section are connected as shown in figure. Temperatures of $A, D$ and $C$ are maintained at $20^{\circ} C, 90^{\circ} C$ and $0^{\circ} C$ . If there is no flow of heat in $A B$ , then ratio of the lengths of $B C$ and $B D$ is

2 / 9

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2 / 7

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Solution

The correct option is C $2 / 7$
Since there is no flow of heat in rod, so temperature of $B$ is equal to temperature at $A$ i.e.,
$θ_{B} = θ_{A} = 20^{\circ} C$
Heat flowing through $D B$ per second $=$ heat flowing through
i.e., $\frac{K A (90^{\circ} - 20^{\circ})}{I_{B D}} = \frac{K A (20^{\circ} - 0^{\circ})}{I_{B C}}$
$∴ \frac{I_{B C}}{I_{B D}} = \frac{2}{7}$ .

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Three conducting rods of same material and cross-section are connected as shown in figure. Temperatures of A,D and C are maintained at 20∘C,90∘C and 0∘C. If there is no flow of heat in AB, then ratio of the lengths of BC and BD is

The correct option is C 2/7Since there is no flow of heat in rod, so temperature of B is equal to temperature at A i.e.,θB=θA=20∘CHeat flowing through DB per second = heat flowing throughi.e., KA(90∘−20∘)IBD=KA(20∘−0∘)IBC∴IBCIBD=27.

Three conducting rods of same material and cross-section are connected as shown in figure. Temperatures of $A, D$ and $C$ are maintained at $20^{\circ} C, 90^{\circ} C$ and $0^{\circ} C$ . If there is no flow of heat in $A B$ , then ratio of the lengths of $B C$ and $B D$ is