The diagram shows light passing through an opening and forming bands.

there is an incident beam of light toward an opening in a grating. the light breaks into 7 different paths labeled n = 3, n = 2, n = 1, n = 0, n = 1, n = 2 and n = 3.
which two order bands are the dimmest?

n = 0 and n = 1
n = 0 and n = 3
n = 1 and n = 2
n = 2 and n = 3

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.