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Two identical conducting rods are first connected separately, each bridging a vessel of water at 100 degree C and a vessel of ice at 0 degree C (rods used independently/in parallel). In the second case the two rods are joined end to end (in series) and bridge the same two vessels. Let q1 and q2 (g/s) be the rates of melting of ice in the first and second cases respectively. Find q2/q1.

1. 1/2
2. 2/1
3. 4/1
4. 1/4

Correct answer: 1/4

Solution

In the first (parallel) case the conductance is 2 times one rod; in the series case it is 1/2 of one rod. So q2/q1 = (1/2)/2 = 1/4.

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