A Si sample with 1016 cm-3 donors is optically excited such that 1019 cm-3 electron/hole pairs are generated per second uniformly in the sample. The light causes the sample temperature to rise to 450 K. Find the quasi-Fermi levels upon shining the light on the sample. Electron and hole lifetimes are both 10 μs. Dp = 12 cm2/s, Dn = 36 cm2/s, ni = 1014 cm-3 at 450 K.

The temperature of air decreases as it is compressed by an adiabatic compressor. a)- true b)- false

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?

Determine whether or not it is possible to compress air adiabatically from k to 140 kpa and 400 k. what is the entropy change during this process?