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Q1 Subjective Hard
Gravitation and other forces prevent Hubble’s-law expansion from taking place except in systems larger than clusters of galaxies. What If? Imagine that these forces could be ignored and all distances expanded at a rate described by the Hubble constant of $$22 \times 10^{-3}\,m/(s . ly)$$. (a) At what rate would the $$1.85m$$ height of a basketball player be increasing? (b) At what rate would the distance between the Earth and the Moon be increasing?

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q2 Subjective Hard
Use Stefan’s law to find the intensity of the cosmic background radiation emitted by the fireball of the Big Bang at a temperature of $$2.73\, K$$.

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q3 Subjective Hard
A star moving away from the Earth at $$0.280c$$ emits radiation that we measure to be most intense at
the wavelength $$500\,nm$$. Determine the surface temperature of this star. 

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q4 Subjective Hard
Difference countries establish different communication satellites in the orbits for their communication system. Are these orbits different ? Explain.

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q5 Subjective Hard
The energy required to excite an atom is on the order of $$1\,eV$$. As the temperature of the Universe dropped below a threshold, neutral atoms could form from plasma and the Universe became transparent. Use the Boltzmann distribution function $$e^{-E/k_BT}$$ to find the order of magnitude of the threshold temperature at which $$1.00\%$$ of a population of photons has energy greater than $$1.00\,eV$$.

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q6 Single Correct Hard
There are two ways to measure the brightness of a star; the apparent magnitude of the brightness of the star is the brightness seen from the earth and absolute magnitude of the brightness of the star which is the brightness of a star seen from the standard distance of ___________.
  • A. $$10$$ parsec
  • B. $$32.6$$ light years
  • C. $$3.26$$ light years
  • D. both (a) and (b)

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q7 Single Correct Hard
Two small balls having equal positive charge $$Q$$ (coulomb) on each are suspended by two insulating
strings of equal length $$L$$, from a hook fixed to a stand. If the whole set up is taken in a satellite
then the angle $$\theta $$ between the two strings is : (in equillibrium)
  • A. $$O^{o}$$
  • B. $$90^{o}$$
  • C. $$180^{o}$$
  • D. $$0 < \theta <180^{o}$$

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q8 Single Correct Hard
Sky looks bright from the earth on a sunny day but from any space station it is dark becuase
  • A. no reflection
  • B. no luminous object
  • C. no natural source
  • D. eye deficiency

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q9 Subjective Hard
Why is the Earth flat at the poles ?

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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Q10 Subjective Hard
Are there some celestial bodies for which the value of acceleration due to gravity is infinity ?

Asked in: Physics - Stars and the Solar System


1 Verified Answer | Published on 16th 11, 2020

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