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A rod CD of thermal resistance 5.0 K/W is attached at the midpoint C of an identical rod AB (so each half of AB also has resistance 5.0 K/W). The ends A, B and D are held at 100 deg C, 0 deg C and 25 deg C respectively. Find the heat current flowing in CD.

1. 4.0 W
2. 5.0 W
3. 6.0 W
4. 8.0 W

Correct answer: 4.0 W

Solution

Balancing currents at junction C (with each half-rod resistance 2.5 K/W and CD = 5 K/W) gives Tc = 45 deg C, so heat current in CD = (45-25)/5 = 4.0 W.

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