What type of spectrum is emitted by a heated solid object (such as the filament of an incandescent bulb)?
A. continuous
B. absorption-line
C. emission-line
D. None of these choices are correct.
Answer: A
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Interstellar dust clouds are best observed at what wavelength?
A) visible only B) radio and infrared C) UV and infrared D) radio and X-ray E) visible and UV
The total kinetic energy of a baseball thrown with a spinning motion is a function of:
a. its linear speed but not rotational speed. c. both its linear and rotational speeds. b. its rotational speed but not linear speed. d. neither its linear nor rotational speed.
In a heat exchanger, as shown in accompanying figure, air flows over brass tubes of 1.8- cm-ID and 2.1-cm-OD that contain steam. The convection heat-transfer coefficients on the air and steam sides of the tubes are 70 W/(m2 K) and 210 W/(m2 K), respectively. Calculate the overall heat transfer coefficient for the heat exchanger (a) based on the inner tube area, (b) based on the outer tube area but assume that a fouling factor of 0.00018 (m2 K)/W has developed on the inside of the tube during operation.
GIVEN
• Air flow over brass tube containing steam
• Tube diameters Inside (Di) = 1.8 cm = 0.018 m
Outside (Do) = 2.1 cm = 0.021 m
• Convective heat transfer coefficients Air side h o= 70 W/(m2 K)
Steam side h i= 210 W/(m2 K)
• Fouling factor on the inside of the tube (Rd) = 0.0018 (m2 K)/W
FIND
• The overall heat transfer coefficient for the heat exchanger based on
(a) the inner tube area (Ui) and (b) the outer tube area (Uo)
ASSUMPTIONS
• The heat transfer coefficients are uniform over the transfer surfaces
SKETCH
Which voltage is not caused by a source of emf?
a. the voltage across a charged capacitor b. the voltage across two copper-iron junctions at different temperatures c. the voltage across the terminals of a dry cell battery d. the voltage from an electric generator