# Project #8075 - homework2

From Chapter 4:

1.    What are the three ways of heat transfer? Give examples for each.

2.    Which way of heat transfer can be done in vacuum?

3.    In hot weather, you go out and feel a metal bar and a wood bar. You feel the metal is much hotter than the wood. Is it really hotter? Why do you feel so?

4.    In cold weather, you go out and feel a metal bar and a wood bar. You feel the metal is much colder than the wood. Is it really colder? Why do you feel so?

5.    Give an example of preventing convection in everyday life. (Winter is a season you need to try hard to prevent heat transfer through convection! There are a lot of examples. )

6.    What are the three ways to state the second law of thermodynamics?

7.    What is the definition of entropy?

8.    Which of the following people’s body has higher entropy: A person who is sick, or a person who is very healthy?

9.    A human body can become more ordered as time goes by, by exercising and eating well; A room can be better organized as time goes by, if somebody works to make it neat; The world can be made better and more peaceful, if we work hard on it. Explain why these facts do not viloate the second law of thermodynamics.

10.    Calculate the maximum possible efficitency of a power plant that borns natural gas at a temperature of 600 K, with low temperature surroundings at 300 K. How much more efficient would the plant be if it were builit in the Arctic where the low temperature reservoire is at 250K? Why don’t we build all power plants in the Arctic?

From Chapter Five:

1.    If two “like charges” (+ and +, or – and -) are put close together, what is the force between each pair?

2.    If two “unlike” charges are put close, what is the force between them?

3.    Which of the following is true about Coulomb’s law? (Choose one answer)
a.    it is a law to describe the gravitational force between two objects.
b.    it is a law to describe the electric force between two objects.
c.    it is a law to describe the magnetic force between two objects.

4.    When considering the electric force between a pair of charges, suppose the distance between the charges remain the same but one of the two charges tripled, how will the magnitude (strength) of the force between them change?

5.    Continue the previous problem, if the charges don’t change, but the distance between them is tripled, how will the force between them change?

6. Lightening is an example of (Choose one)
a. like charges repel.
b. unlike charges attract.

7. In dry weather, you brush your hair with plastic brush, your hair sticks out and does not want to stay put. Explain this phenomenon with the basic electric forces. (i.e., like charges repel, unlike charges attract.)

 Subject Science Due By (Pacific Time) 06/27/2013 12:00 am
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