Most coal deposits were formed in the
A) Cenozoic era.
B) Mesozoic era.
C) Paleozoic era.
D) Precambrian era.
Answer: C
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A beam of photons of wavelength 0.55 nm undergoes Compton scattering from free electrons.What is the momentum of the photons that emerge at a 55° angle with respect to the incident beam?
a. 1.20E–24 kg·m/s b. 1.20E–33 kg·m/s c. 3.65E–34 kg·m/s d. 8.31E+23 kg·m/s
During a total solar eclipse, what part of the Sun is often visible that we normally cannot see?
a. core b. CMEs c. corona d. photosphere e. solar wind
A copper sphere 2.5 cm in diameter is suspended by a fine wire in the center of an experimental hollow cylindrical furnace whose inside wall is maintained uniformly at 430°C. Dry air at a temperature of 90°C and a pressure of 1.2 atm is blown steadily through the furnace at a velocity of 14 m/s. The interior surface of the furnace wall is black. The copper is slightly oxidized, and its emissivity is 0.4. Assuming that the air is completely transparent to radiation, calculate for the steady state (a) the convection heat transfer coefficient between the copper sphere and the air, and (b) the temperature of the sphere.
GIVEN
• A copper sphere suspended in a furnace with air flowing over it
• Sphere diameter (D) = 2.5 cm = 0.025 m
• Sphere emissivity (?) = 0.4
• Furnace wall temperature (Tw) = 430°C = 703 K
• Air temperature (Ta) = 90°C = 363 K
• Air pressure (pa) = 1.2 atm
• Air velocity (U?) = 14 m/s FIND (a) The convective heat transfer coefficient ( ) ch (b) The temperature of the sphere (Ts) ASSUMPTIONS
• Steady state
• The air behaves as an ideal gas
• The furnace can be treated as a black body enclosure
• Only the density of the air varies with temperature
SKETCH
Which of the following rocks would be the first to weather in a humid climate? Which would be the last? Defend your answers. (a) granite (b) sandstone (c) limestone (d) halite
What will be an ideal response?