# Physics Exam: Stars and Planets

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## 29 Questions

0.3 R⊙

10^(-3) L⊙

### What assumption about the star's emission is made in the problem?

It emits as a blackbody.

### What is the goal of part (i) of the original problem?

Determine the surface temperature of the star and calculate the wavelength at which its spectrum will peak.

### In what part of the electromagnetic spectrum would you expect the star's peak wavelength to be?

Infrared or far-infrared range

### What can be inferred about the star's properties based on its luminosity and radius?

It is likely a low-mass, low-temperature star.

### What is the primary reason why most stars are found on the main sequence?

The main sequence is the stage of a star's life where it fuses hydrogen into helium, which is the most stable and long-lasting phase.

### What is the ratio of the radii of Venus and Saturn?

0.104 R⊕/9.1 R⊕ = 0.011

### Describe the physical characteristics of sunspots.

Sunspots are dark regions on the Sun's surface, cooler than the surrounding areas, with strong magnetic fields and intense solar activity.

0 hours

### How do the properties of sunspots relate to the solar magnetic field and the rotation of the Sun?

Sunspots are areas of strong magnetic fields, which are amplified by the Sun's differential rotation, leading to the formation of active regions and sunspot cycles.

### Which moon of Jupiter has a stronger tidal effect on Jupiter, Io or Ganymede?

Ganymede, despite being farther away, has a stronger tidal effect on Jupiter due to its larger mass and resulting differential gravitational force.

### What is the configuration of the Sun, Earth, and Jupiter when Jupiter is at opposition?

The Earth is between the Sun and Jupiter.

P = GMρ/ 2R

### What is Kepler's Second Law of Planetary Motion, and how does it relate to conservation of angular momentum?

Kepler's Second Law states that the line connecting the planet to the Sun sweeps out equal areas in equal times, which is a direct result of the conservation of angular momentum (mvr).

### Where do main sequence stars, the Sun, red giants, and white dwarfs lie on a Hertzsprung-Russell diagram?

Main sequence stars lie on the diagonal, the Sun is near the middle, red giants are at the top right, and white dwarfs are at the bottom left.

### How does the speed of an asteroid change at perihelion and aphelion, and what would be required to make its orbit circular?

Using the vis-viva equation, the asteroid's speed can be calculated at perihelion and aphelion. To make the orbit circular, the speed would need to change by a factor dependent on the eccentricity and semi-major axis.

### What is the relationship between the sidereal period and the synodic period of Jupiter?

The synodic period of Jupiter is shorter than its sidereal period.

### What is the purpose of detecting extrasolar planets, and how does it relate to understanding planet formation?

Detecting extrasolar planets provides a lot of information about the final outcome of planet formation.

### How can radiometric dating help determine the formation of our solar system?

Radiometric dating can help determine the formation of our solar system by providing information about the age of rocks and meteorites, which can be used to reconstruct the sequence of events that led to the formation of our solar system.

### What is meant by 'nonrelativistic electron degeneracy pressure' and why is it important for white dwarf stars?

Nonrelativistic electron degeneracy pressure refers to the pressure exerted by degenerate electrons in a white dwarf star, which supports the star against collapse.

### How does the relationship between pressure and density in electron degeneracy pressure affect the mass and radius of white dwarf stars?

The relationship between pressure and density in electron degeneracy pressure results in a scaling of the radius with the mass of the star, such that the most massive white dwarfs are expected to have the smallest radii, with R ∝ M^(-1/3).

### What can be inferred from the angular position of a star oscillating on a period of 1 year, with a maximum excursion of ±0.25 arcseconds?

This suggests that the star has an orbiting companion, possibly a planet, which is causing the star's position to oscillate.

### How can you determine that an object detected orbiting a star is a planet and not a star?

You can determine that the object is a planet and not a star by analyzing its mass, orbit, and other characteristics, such as its surface temperature and luminosity.

### What is the physical principle that relates the luminosity and surface temperature of a star?

Stefan-Boltzmann equation

### What is the type of distribution that describes the spectral energy distribution of a star?

Planck distribution

3

arcseconds

### What is the physical principle that explains the shift in wavelength of light emitted by the binary stars due to their motion?

Doppler effect

This is a 2-hour exam paper for BSc/MSci in Physics and Physics Joint Honours, covering topics related to stars and planets. It consists of two sections: Section A with 8 questions and Section B with 2 questions. The exam is designed to test students' understanding of the subject.

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