11this is the fig. for those who need---
Consider two identical spheres,one of which lies on a thermally insulating plate and the other hangs on an insulating
thread.Equal amounts of heat is given to the 2 spheres. Which will have a higher temp. ??
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12 Answers
1The ball on the insulating plate will have a higher temperature. In the suspended ball, the surface area in contact with air is more, so there is lot of loss in temperature.
It is comparitively less in the ball on the insulating plate.
19according to the first law of thermodynamics;
δQ = δ U + δW
when the spheres are heated volumetric expansion occurs . thus c.g. goes up for the first sphere and comes down for the second sphere(as suggested from figure and practical situation)......hence δW is positive for the first sphere and negative for the second sphere;
if we put the second law differently for the 2 spheres :
δQ=δU1 + δW1
δQ=δU2 + δW2
hence as δW1 is postive and δW2 is negative.....it turns out that
δU2>δU1....(GETTING BY ADDING A POSITIVE AND NEGATIVE QTY. TO THE SAME δQ IN THE FIRST AND SECOND EQN. RESPECTIVELY)
THUS SECOND SPHERE HAS HIGHER TEMP THAN FIRST SPHERE!!!
24problem in first line.......
differential for mof 1st law is
δq=dE+δW
becoz internal energy is independent of path whereas q and w are dependent on path followed [1]
19consider Q = U+ W.....THAT IS SIMPLER......anyways the logic remains the same anyway !!!!! do you have any other explanation?
24ur xplaiantion is ok dude,............and that simpler form also works well[1][1]
i was just correcting u about using differential form
3hey ronald where did u get this problem.i havent seen these type of pbms.
3standard FIITJEE question .......!!!!! seen it a couple of times as an assertion reasoning question!!!!
11@ sanjit- even i thought like you @ first but then u c both are having only one point of contact..so both are exposed the same to air.
11hey msp this was from a book called -- "200 puzzling problems in physics"
1have seen this one in some test before.. the catch in the problem shud be , that when both balls are given heat and their temps rise, both balls expand., now when the lower ball is gonna expand, its gonna 'gain gravitational potential energy' , while the one thats hanging, is gonna 'loose gravitational potential energy', now, when both are given equal amount of heat energy, some amount of energy is used by the lower ball, to rise its potential energy, but the upper balls uses the entire of it to rise its temp.
so the upper one shud have higher temp.
cheers!!