Suppose that an intrinsic semiconductor has 500 free electrons per cubic centimeter at room temperature. If the temperature changes to 100 degrees C, which of the following better describes the concentration of holes in the semiconductor?

a. greater than 500 holes per cubic centimeter
b. equal to 500 holes per cubic centimeter
c. lower than 500 holes per cubic centimeter
d. None of the above.
e. There are no free electrons or holes in an intrinsic semiconductor.

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?