Homeworks 6

Homework 6 due on 10/12/2009

Problem 1

Assume that you need on average 1 kilowatt of power continuously, day and night, to support your life style. Some of the energy is used as electricity, but much is used to manufacture and run your automobile and other possessions. One Watt is $10^{7}$ ergs/sec.

1. Suppose you live for 70 years, how many ergs of energy will you use up?

2. Using $E=mc^{2}$, how much mass would have to be converted to energy to create this much energy?

3. Suppose the energy is created by fusing hydrogen into helium. How many grams of hydrogen would be needed? Remember that only 0.71\% of the mass is converted to energy during this reaction.

Problem 2

What, specifically, is a theoretical model for a star? How are theoretical models produced? What are the most important physical processes that need to be included to give accurate models?

Problem 3

Describe hydrostatic (pressure) equilibrium in stars. Hydrostatic equilibrium means that stars must have higher pressure at their centers than at their surfaces. Why? What kinds of behavior can a star have if it is not in hydrostatic equilibrium? Give examples of stars not in hydrostatic equilibrium.

Problem 4

How many kinds of neutrinos are there? Why is this important for measuring the properties of the sun?

Problem 5

Estimate the central density and temperature of a star with one solar mass and radius. (Hint: Use the equations for hydrostatic equilibrium, assume an ideal gas, and a 'one zone' model with reasonable boundary conditions). Compare the results with values from literature.