A standard candle is ________
A) a light source of known luminosity B) a 7-cm-long wax candle
C) another name for a main-sequence star D) another name for a barred-spiral galaxy
A
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Which of the following sequences of electromagnetic radiation is arranged in the order of increasing energy?
A) Gamma rays, X-rays, infrared radiation, and radio waves B) Radio waves, microwaves, gamma rays, and ultraviolet radiation C) Visible light, ultraviolet radiation, X-rays, and gamma rays D) Visible light, microwaves, radio waves, and infrared radiation
The image below shows a rock formation nicknamed “the face on Mars” that was taken by the Viking 1 orbiter in 1976. Given the clear resemblance to a face, what is an appropriate scientific reaction to this image?
A) Assume it is most likely a coincidental result of light and shadow, and plan higher resolution follow-up observations.
B) Assume that the image is probably evidence of an advanced civilization, and develop plans to attempt radio communication wit the civilization.
C) Conclude that the resemblance to a human face is so clear that it cannot have been made by nature and that this geological feature must have been built by an advanced civilization.
D) Assume that NASA's spacecraft must have been hacked by someone perpetrating a hoax, and therefore ignore the image
If a star is over ________ solar masses, its core can collapse to a black hole in a hypernova
A) 1.4 B) 3 C) 8 D) 25 E) 100
A wire of perimeter P and cross-sectional area A emerges from a die at a temperature T (above ambient temperature) and with a velocity U. Determine the temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions.
GIVEN
• A wire emerging from a die at a temperature (T) above ambient
• Wire perimeter = P
• Cross-sectional area = A
• Wire emerges at a temperature T above ambient
• Wire velocity = U
FIND
• The temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions
ASSUMPTIONS
• Ambient temperature is constant at T?
• Heat transfer coefficient between the wire and the air is uniform and constant at hc
• The material properties of the wire are constant
? Thermal conductivity = k
? Thermal diffusivity = ?
• Axial conduction only
• Wire temperature is uniform at a cross section (negligible internal thermal resistance)
SKETCH
