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Study Problems Exam 2 questions and answers verified 2024
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Study Problems Exam 2 questions and answers verified 2024
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Study Problems Exam 2Describe the properties and everyday uses of CCDs (charge coupled
devices). - correct answer ✔CCDs contain millions of pixels. They are much
more sensitive than photographic plates and are now used in mosaics, by
astronomers, to cover a large field on the sky. Their everyday uses are in
digital cameras and cell phones.
How does the resolution of a telescope above the atmosphere depend on the
size of the mirror? - correct answer ✔The larger the mirror, the better the
resolution, i.e. the sharper the images.
How much larger is the Sun than the Earth in diameter? In volume? - correct
answer ✔The diameter of the Sun is about 100x the diameter of the Earth.
Thus, the volume of the Sun is about 10^6 x the diameter of the Earth, i.e. if
the Sun were hollow it would take 10^6 Earth-sized objects to fill it.
What is the average density of the Sun? How does this compare with water? -
correct answer ✔The average density of the Sun is 1400 kg/m^3. This is
similar to that of water (1000 kg/m^3).
What is hydrostatic equilibrium for the Sun? - correct answer ✔Hydrostatic
equilibrium is a balance between the outward gas pressure force in the Sun
and the inward pull of gravity. The Sun supports its own weight by its outward
gas pressure force, so that it is neither contracting nor expanding.
What is thermal equilibrium for the Sun? - correct answer ✔Thermal
equilibrium is a state in which the energy radiated by the photosphere of the
Sun is replaced by an internal energy source, nuclear fusion in the core.
, What are the central and surface temperatures of the Sun? - correct answer
✔The central temperature of the Sun is about 1.6 x 10^7 K and the
temperature in the photosphere is about 5800 K.
What are the two most abundant elements in the Sun? - correct answer
✔Hydrogen and helium are the two most abundant elements in the Sun (as
well as in the universe as a whole).
What is the physical state of the material in the Sun? - correct answer
✔Below the photosphere of the Sun, the hydrogen and helium in the Sun are
in an ionized state, i.e. the electrons move freely rather than being bound to a
particular nucleus.
What type of particle is a normal hydrogen nucleus? - correct answer ✔A
normal hydrogen nucleus is a proton.
What is the energy source of the Sun? Describe the physical process that
releases energy. Discuss where this process occurs in the Sun and why it
occurs here. - correct answer ✔The Sun produces energy by the
thermonuclear fusion of hydrogen to helium in its core. Through a series of
reactions, four hydrogen nuclei are fused to produce one helium nucleus plus
energy. The mass of a normal helium nucleus is slightly less than four times
the mass of a normal hydrogen nucleus. The lost mass is converted to an
equivalent amount of energy according to the relation E=mc^2. Nuclear fusion
occurs only in the core of the Sun, since it is only there that the temperature is
sufficiently high (T>10^7K). High temperature is required for nuclear fusion,
since nuclei must collide at high speed in order to overcome their electrical
repulsion.
About how long has the Sun been in existence and about how much longer
will the Sun's present nuclear energy reserve last? - correct answer ✔The
Sun has been in existence for 5 billion years. The Sun's present hydrogen
energy reserve will last for another 5 billion years.
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