If the voltage amplitude across an 8.50-nF capacitor is equal to 12.0 V when the current amplitude through it is 3.33 mA, the frequency is closest to
A) 32.6 MHz.
B) 5.20 MHz.
C) 32.6 kHz.
D) 5.20 kHz.
E) 32.6 Hz.
B
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Cooled air is flowing through a long sheet metal air conditioning duct, 0.2 m high and 0.3 m wide. If the duct temperature is 10°C and passes through a crawl space under a house at 30°C, estimate
(a) The heat transfer rate to the cooled air per meter length of duct.
(b) The additional air conditioning load if the duct is 20-m-long.
(c) Discuss qualitatively the energy conservation if the duct were insulated with glass
wool.
GIVEN
• An air conditioning duct in a crawl space
• Duct height (H) = 0.2 m
• Duct width (w) = 0.3 m
• Duct temperature (Ts) = 10°C
• Ambient temperature (T?) = 30°C
FIND
(a) The heat transfer rate per meter length (qc/L) to the cooled air in the duct
(b) The additional air conditioning load (q20) if the duct length (L) = 20 m
(c) Discuss qualitatively the energy conservation if the duct were insulated with glass wool
ASSUMPTIONS
• Ambient air is still
• Duct temperature is constant and uniform
• Radiation is negligible
• Edge effects are negligible
• No condensation on the duct surface
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 20°C
Thermal expansion coefficient (?) = 0.00341 1/K
Thermal conductivity (k) = 0.0251 W/(m K)
Kinematic viscosity (?) = 15.7 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron?
A) toward the north B) toward the south C) upward D) downward E) toward the west.
The air we breathe is mostly oxygen
Indicate whether the statement is true or false
The New Orleans levees failed because
A. thermal expansion broke them B. they were made of continuous concrete that could not stand the pressure C. they had leaks at the thermal expansion joints D. they were weaker at the thermal expansion joints