Why does the average chemical composition of stars now forming differ from that of older stars?
What will be an ideal response?
The first stars formed from gas that was metal poor, and the only survivors of these early generations are low-mass, long-lived stars. Their spectra, which indicate the composition of their atmospheres and not their cores, still show the composition of the metal-poor gas from which they formed. Population I stars such as the Sun formed more recently, after the interstellar medium had been enriched in metals, and their spectra show stronger metal lines. Stars forming now have even higher metal abundances.
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Nuclear Binding Energy: A beryllium-8 nucleus at rest undergoes double alpha decay as follows:
The known atomic masses are:
What is the kinetic energy of each departing alpha particle? (1 u = 931.5 MeV/c2)
A. 46 keV B. 65 keV C. 92 keV D. 130 keV E. 180 keV
Conduction: The thermal conductivity of a certain concrete is 0.80 W/m . K and the thermal conductivity of a certain wood is 0.10 W/m ? K. How thick would a solid concrete wall have to be in order to have the same rate of heat flow through it as an 8.0-cm thick wall made of solid wood? Both walls have the same surface area and the same temperature difference across their faces.
A. 53 cm B. 64 cm C. 71 cm D. 85 cm
In which case can total internal reflection occur? nwater = 1.333, nglass = 1.50, nair = 1.000
A. At the interface between glass and water, when traveling in glass. B. At the interface between glass and water, when traveling in water. C. At the interface between air and water, when traveling in air. D. At the interface between air and glass, when traveling in air.
According to the quantum mechanical model of the hydrogen atom, if the orbital angular momentum quantum number is ?, there will be how many permitted magnetic quantum numbers?
A) ?/2 B) 3? C) 2? D) 2? - 1 E) 2? + 1