Physics 114 –Morning Session, Summer 2006

Participation Points #1

This is an in-class work, to be turned in at the end each discussion session. No points when absent.

Use provided space to show your work only, use back page for notes

 

Student’s Name:_______________________       Team #______________

 

 

 

 

 

 

 

 

 

 

 

1.-           (a) If system A is not in thermodynamic (TD) equilibrium with system B, and B is not in equilibrium with C, can you draw any conclusions about the temperatures of the three systems? Circle an answer.                             Yes                          No

(b) A thin layer of glass does not offer much resistance to heat conduction. Yet double-glazed windows provide substantial energy savings. Why? Answer in one phrase.

 

(c) What’s the dominant mode of heat loss from a red-glow burner? ________________What’s the dominant mode of heat transfer from burner to pan                ______________________; from bottom of pan to top of water surface_________________________

 

2.-            Specific Heat. A piece of copper at 300oC is dropped into 1kg of water at 20oC, if the equilibrium temperature is 250C, what is the mass of the copper. Hints: heat loss by copper equals heat gain by water, use specific heat values from table.

 

 

 

 

 

 

 

 

 

3.-            Heat Transfer. A 8m x 10m basement is built on a concrete slab 25cm thick. What is the heat loss rate through the concrete floor if indoor temperature is maintained at 20oC while the ground is at 10oC? Hints: use value for thermal conductivity of concrete from table.

 

 

 

 

 

 

 

 

 

4.-            (a) Why are you supposed to check the pressure in a tire when the tire is cold? One phrase answer:

 

 

(b) Two different gases are at the same temperature, and both are at low densities that they behave like ideal gases. Do their molecules have the same thermal speeds? Explain in one phrase.

 

 

(c) Why do we use the triple point of water for thermometer calibration? Why not just the melting point or the boiling point?

 

 

 

5.-            Gases. A dorm room measures 3m x 3m x 2m, (a) how many air molecules does it contain (hint: assume air is an ideal gas)

 

 

 

 

(b) What is the total translational KE of these molecules? (hint:in an ideal gas, thermal energy provide translational KE)

 

 

 

(c) How is this energy compared to the KE of a 2000kg car going at 108km/h?

 

 

 

 

 

 

6.-            Phase Changes. A 250g piece of ice at 0oC is placed in a 500W microwave oven which runs for 5 min. What is the temperature at the end of this time? (Hint: check if total enerfy supplied by oven can melt the ice and then increase its temperature, use heat of transformation and specific heat for ice and water from tables)

 

 

 

 

 

 

 

 

 

 

7.-            (a) You bring a pot of water to boil, then forget about it. Ten minutes later you come back to the kitchen to find the water still boiling. What’s its temperature?

 

 

(b) Why is it the specific heat at constant pressure greater than at constant volume?

 

 

 

(c) When a system is in TD equilibrium -What’s the average energy per molecule _______________

What’s the theorem you used __________________

 

8.-            TD Processes: Isothermal. How much work does it take to compress 25 mol of an ideal gas to half its original volume while maintaining a constant temperature of 300 K? (Hint: for an ideal gas, the work done along an isotherm  is proportional to thenatural  log of volumes)

 

 

 

 

 

 

 

 

 

 

 

 

9.-            TD Processes: Adiabatic. A bike pump is a 30cm long cylinder with the handle all the way out. The pump contains air (γ=1.4) at 20oC. If the pump outlet is blocked and the handle pushed until the internal length of the pump cylinder is 10cm, by how much does the air temperature rise? Assume no heat is lost. (Hint: adiabatic PVγ=constant, write P in term of T using ideal gas equation)