Why is the Cepheid's period related to their luminosity?
What will be an ideal response?
The longer-period Cepheids are about 40,000 times more luminous than the Sun, and very massive stars, whereas the shortest-period Cepheids are only a few hundred times more luminous than the Sun, and lower mass stars.
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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
A resistor is made out of a long wire having a length L. Each end of the wire is attached to a terminal of a battery providing a constant voltage V0. A current I flows through the wire
If the wire were cut in half, making two wires of length L/2, and both wires were attached to the battery (the end of both wires attached to one terminal, and the other ends attached to the other terminal), what would be the total current flowing through the two wires? A) 4I B) 2I C) I D) I/2 E) I/4
The photons of blue light have:
A) more energy than the photons of red light. B) more energy than the photons of ultraviolet light. C) a lower frequency than the photons of red light. D) a longer wavelength than the photons of red light.
The Doppler radial velocity technique works best for
A) planets whose orbits are along are line of sight. B) planets whose orbits are perpendicular to our line of sight. C) planets whose orbits are nearly circular. D) planets whose orbits are very eccentric.