How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected?
A) by extrapolation
B) through observations of the 21 cm line of atomic hydrogen
C) through observations of spectral lines of dark matter
D) by watching the galaxies rotate over a period of years
E) by measuring the broadening of absorption lines
B
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A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10 cm thickness is 20 W/m2 . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in
IVEN
• Concrete wall
• Thickness (L) = 100 cm = 0.1 m
• Heat loss (q/A) = 20 W/m2
• Surface temperature
? Inner (Ti) = 22°C
? Outer (To) = 6°C FIND
• The thermal conductivity (k) and compare it to the tabulated value
ASSUMPTIONS
• One dimensional heat flow through the wall
• Steady state conditions exist
SKETCH
The ozone layer lies at the boundary of the stratosphere and mesosphere
Indicate whether the statement is true or false
An electron is in an infinite square well (a box) that is 8.9 nm wide. What is the ground state energy of the electron? (h = 6.626 × 10-34 J ? s, mel = 9.11 × 10-31 kg, 1 eV = 1.60 × 10-19)
A) 0.0048 eV B) 0.0057 eV C) 0.0066 eV D) 0.0076 eV E) 0.0085 eV
Sustainability in a resource means
a. ever increasing amounts of the resource. b. doubling the amount needed means doubling the amount available. c. the amount of the resource grows as the population grows. d. production of the same amount of the resource forever. e. production of gradually decreasing amounts of the resource.