Physics - Heat & Thermo Question with Solution | TestHub
In the 1840s Colding, independently of Mayer and Joule, did a series of experiments that led to a reasonable value of the mechanical equivalent of heat. The experiment can be summarized as follows: A heavy sled is pulled along some rails. Colding measured the force on the sled and the distance traveled, and then calculated the work done. The rails get warmer but Colding did not try to measure the rise in temperature. Instead he measured very carefully the expansion of the rails. From that he calculated the rise in temperature. From the rise in temperature, the mass of the rails, and the specific heat capacity of the rails (he used a lot of different materials), Colding calculated the amount of heat necessary to give the same rise in temperature as found by the experiment. By postulating that the work done by the force is equal to the amount of heat produced by the force, he calculated the mechanical equivalent of heat and found the value J/cal. The accepted value today is J/cal. Assume that he applied the same force in each case, used the sled of same mass and slid them the same distance. But the rails were of different material in each case. Assume that there is no heat loss and the entire energy is given to the rails only.
Which of the following can be a reason that the mechanical equivalent of heat was measured to be lesser than the true value?
Options:
Answer:
Solution:
If some heat is lost, the heat given to the rails is less than the work done:
Colding neglected the loss, so:
Neglecting heat loss makes the measured value more than the true value, not less. So neither (A) nor (B).
