Podcast
Questions and Answers
Which equation correctly expresses the relationship between the radius (R) and the mass (M) of a star under the assumption of uniform density and hydrostatic equilibrium?
Which equation correctly expresses the relationship between the radius (R) and the mass (M) of a star under the assumption of uniform density and hydrostatic equilibrium?
- $R hickapprox (M)^{3/2}$
- $R eq (M)^{1/3}$
- $R eq (M)^{-1/3}$
- $R hickapprox (M)^{-1/3}$ (correct)
What is the significance of deriving an expression for free-fall time in astrophysical contexts?
What is the significance of deriving an expression for free-fall time in astrophysical contexts?
- It calculates the speed of light in various celestial objects.
- It estimates the time taken for a cloud to collapse due to gravitational force. (correct)
- It predicts the behavior of stars in hydrostatic equilibrium.
- It helps determine the temperature of collapsing gases.
How does a Quasar differ from a Radio galaxy?
How does a Quasar differ from a Radio galaxy?
- Quasars reside in elliptical galaxies, while Radio galaxies are found in spiral galaxies.
- Quasars are stationary, while Radio galaxies exhibit significant motion.
- Quasars are primarily visible in the optical spectrum, while Radio galaxies are visible in the ultraviolet spectrum.
- Quasars exhibit higher luminosity and are powered by supermassive black holes, while Radio galaxies are less luminous. (correct)
What does the calculation of the half-width of a spectral line at a given temperature reveal?
What does the calculation of the half-width of a spectral line at a given temperature reveal?
Which physical constant is NOT directly used when calculating the half-width of a spectral line for H-atoms?
Which physical constant is NOT directly used when calculating the half-width of a spectral line for H-atoms?
What is the primary reason the Bolometric correction is necessary in astronomy?
What is the primary reason the Bolometric correction is necessary in astronomy?
Which statement accurately describes the significance of the Hayashi line in the H-R diagram?
Which statement accurately describes the significance of the Hayashi line in the H-R diagram?
What does Rayleigh's criterion specifically relate to in telescope operation?
What does Rayleigh's criterion specifically relate to in telescope operation?
Considering a star made of a monoatomic gas, what does the Virial theorem suggest about the stable conditions in a star?
Considering a star made of a monoatomic gas, what does the Virial theorem suggest about the stable conditions in a star?
What defines a degenerate gas in terms of its physical state?
What defines a degenerate gas in terms of its physical state?
In the context of galaxy classification, which type of galaxies is classified as having a smooth and featureless appearance?
In the context of galaxy classification, which type of galaxies is classified as having a smooth and featureless appearance?
Which of the following best describes the concept of the expanding universe?
Which of the following best describes the concept of the expanding universe?
What holds true about the magnitude limit of a 1.04 m telescope in the visible range?
What holds true about the magnitude limit of a 1.04 m telescope in the visible range?
Flashcards
Free-fall time
Free-fall time
The free-fall time is the time it takes for a cloud of gas to collapse under its own gravity. It is calculated by dividing the initial radius of the cloud by the speed of free-fall, which is proportional to the square root of the gravitational acceleration.
Rotation curve of a galaxy
Rotation curve of a galaxy
The rotation curve of a galaxy shows the velocity of stars and gas at various distances from the galactic center. A flat rotation curve indicates that the mass distribution in a galaxy extends far beyond what's visible in its visible light, suggesting the presence of dark matter.
Distinguish between a Quasar and a Radio galaxy
Distinguish between a Quasar and a Radio galaxy
A quasar is a highly luminous and distant active galactic nucleus (AGN) that is thought to be powered by a supermassive black hole accreting matter. A radio galaxy is also an AGN, but it emits a strong jet of radio waves from its core. The key difference is the strength and direction of their radio emission.
Unified model for active galaxies
Unified model for active galaxies
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Half-width of a spectral line
Half-width of a spectral line
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Luminosity Ratio
Luminosity Ratio
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Hubble's Galaxy Classification
Hubble's Galaxy Classification
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Bolometric Correction
Bolometric Correction
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Magnitude Limit of a Telescope
Magnitude Limit of a Telescope
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Solar Corona Temperature
Solar Corona Temperature
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Hayashi Line
Hayashi Line
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Expanding Universe Evidence
Expanding Universe Evidence
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CNO Cycle
CNO Cycle
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Study Notes
PHE-15: ASTRONOMY AND ASTROPHYSICS
- Exam Details:
- Bachelor of Science (B.Sc.) Term-End Examination, December 2014
- Physics
- Time: 2 hours
- Maximum Marks: 50
- Note: Attempt all questions. Values of physical constants are provided at the end of the exam paper. Symbols have their usual meanings. Students can use non-programmable calculators or log tables.
Question 1:
- Instructions: Attempt any five parts from the given options.
- (a): Compare the luminosity of a main sequence star to the Sun if the main sequence star is 10 times more massive than the Sun.
- (b): Sketch Hubble's scheme of galaxy classification.
- (c): Define Bolometric correction. Explain why it is required.
- (d): Determine the magnitude limit detectable with a 1.04 m telescope in the visible range.
- (e): Explain what indicates the temperature of the solar corona is about 10⁶ K.
- (f): Explain the significance of the Hayashi line in the H-R diagram.
- (g): Provide two arguments supporting the expanding universe compared to the steady-state universe.
- (h): Describe the complete CNO cycle nuclear reactions.
Question 2:
- (a): Explain Rayleigh's criterion for the resolving limit of a telescope.
- (b): Identify factors determining the resolving power of a telescope.
- (c): Discuss how light-gathering power affects a telescope's resolving power.
- (d): Calculate the resolving power of a 2-meter telescope for a wavelength of 500 nm (in arc-seconds).
Question 2 (Alternative):
- Instructions: Explain the universal equatorial system of coordinates, using a diagram. Show the equatorial coordinates of the Sun at the summer and winter solstices.
Question 3:
- Instructions: Starting with the equation of hydrostatic equilibrium and considering a monoatomic stellar gas, derive the Virial Theorem.
- Alternative: Describe the nebular model used to explain the formation of the solar system. Discuss if the present angular momentum distribution in the solar system is consistent with the nebular model.
Question 4:
- (a): Define a degenerate gas and explain how it is different from an ideal gas.
- (b): Assuming a uniformly dense star in hydrostatic equilibrium, prove that R ∝ M⁻¹/³ (where R is the radius and M is the mass).
- (c): Analyze the significance of the relationship between radius and mass in stellar structures.
- (Alternative): Derive an expression for the free-fall time. Calculate the free-fall time of a collapsing cloud of neutral hydrogen with an initial number density of 10⁶ m⁻³ and discuss the rotational curve of the Milky Way Galaxy.
Question 5:
- (a): Differentiate between a quasar and a radio galaxy.
- (b): Assuming Hydrogen atoms to be the emitters, calculate the half-width of a spectral line with a wavelength of 580 nm and a temperature of 6 × 10⁵ K.
- (Alternative): Explain the unified model for active galaxies.
Physical Constants (provided in the document):
- Values of physical constants are listed in the document. These include constants for radius (R), mass (M), luminosity (L), Gravitational constant (G), Boltzmann constant (kb), mass of a proton (M), speed of light (c) and 1 parsec (pc).
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Description
This quiz covers concepts from the Astronomy and Astrophysics course, part of the Bachelor of Science (B.Sc.) program. Topics include stellar luminosity, galaxy classification, and the significance of the H-R diagram. Test your knowledge and understanding of key astrophysical principles and observations.
