Which of the following statements explain why the two-source interference equations are not valid for an observer far away from two red LED signal lights? 1. not monochromatic sources
2. incoherent sources
3. observed from a distance similar to or smaller than the separation between the sources

a. 1 only
b. 2 only
c. 3 only
d. 1 and 2 only
e. 1 and 3 only
f. 2 and 3 only
g. all three

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.