Question

Questions See the last page for thermodynamic constants that may be need to answer questions and problems. 1. (2) Fully explain why the following sentence is incorrect (i.e. use some terminology incorrectly). "The sun heated the sidewalk and now the sidewalk has a lot of heat." 2. (4) A piece of iron and a piece of copper with equal masses but different temperatures are put in thermal contact and isolated from their surroundings. They exchange heat until they reach thermal equilibrium. Answer the following by circling your choice in each case. Which material undergoes the greater heat transfer? (Iron, copper, same) a. b. Which material undergoes the greater temperature change? (Iron, copper, same) (2) A glass stopper is inserted into the top of a pyrex bottle and gets stuck. To loosen the stopper, which of the following will work? Circle your choice: 3. Heat the stopper and bottle a. Cool the stopper and bottle b. Neither will help. c. (2) Consider a hole you drill in a sheet of metal. Circle your choice: If you heat the metal, the diameter of the hole gets (larger, smaller, does not change.) 4.

Answer 1

1) The heat is a form of energy flow. Heat can flow from one body to another, increasing the thermal energy or temperature of the second body. But we can not say that there is a lot of heat in the body. Heat is only defined if there is a flow. The stored energy is either referred to as thermal energy or temperature. So, the sidewalk has a lot of thermal energy (or has a high temperature) is the correct statement.

2) a) Since the system is isolated from its surroundings, the only heat flow that can occur is from the hotter metal to the cooler metal. Whatever heat is released by the hotter object is received by the cooler object. So, Both undergo the same heat transfer.

b) The change in temperature depends on the specific heat (heat required to change the temperature) of the solids, since they are of same mass.

Iron has a higher specific heat than copper. This means that it takes more heat to change the temperature(heat or cool) iron. So, the change in temperature is greater for copper.

3) Pyrex is a form of tempered glass that expands and compresses very less by heating or cooling.

Given that the glass stopper is made of ordinary glass, we can coll both the objects such that the ordinary glass cork will compress more and loosen.

4) Metals expand uniformly when they are heated. So, the size of the hole reduces, as the parts of metal that borders with the hole expands and takes up the space for the hole.