Assuming you are not using a refrigerator to keep T constant, compare the time i

Question

Assuming you are not using a refrigerator to keep T constant, compare the time it takes for the silver block to heat from 100 K to 105 K to the time it takes to heat from 105 K to 110 K. -- answer is C. But i think it is A.. how do we get C? I need solution, thanks.

The next two problems are related to the following situation: Low temperature physicists need to pump heat away from their samples, to keep the environment from heating the samples up. To model this, consider a copper wire connected to a 100-K silver block at the "sample" end and to the room temperature (293 K) environment at the other end, as shown below. The wire has length 0.5 m, cross sectional area 0.03 mm', and thermal conductivity 400 W/m-K. Cu wire Room Silver block 100 K Temperature 293 K 5. How much heat per second needs to be removed from the block to keep its temperature constant? (For this problem, ignore the heat capacity of the copper wire) a. 4.6 x103 w b, 2.1 x 10-2 w C. 8.7 x 10.2 W d. 35 W e. 42,000 w 6. Assuming you are not using a refrigerator to keep T constant, compare the time it takes for the silver block to heat from 100 K to 105 K to the time it takes to heat from 105 K to 110 K. t100 105 > t100105 t100 105

Explanation / Answer

rate of heat transfer = k A delta(T) / d

5. P = (400) (0.03 x 10^-6) (293 -100) /0.5

P = 4.6 x 10^-3 W

Ans(a)

6. as temp of silver block increases, delta(T) decreases.

so rate of heat transfer also decreases.

so it will start to take greater time.

Ans: (c) t100->105 < t105->110

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