PHYS- Chapter 16

28. How much radiant energy from the Sun, on average, reaches each square meter at the top of Earth's atmosphere each second?

1400 J. This input energy is called as solar constant. This value can be expressed in terms of power as 104 w/.

19. Which will normally warm faster, a black pot pf cold water or a silvered pot of cold water?

A black pot of cold water normally heats faster than a silver pot of cold water because the color black is a better absorber of heat radiation as compared to silver.

5. Does a good insulator prevent heat from escaping, or does it simply slow its passage?

A good insulator prevents heat from getting through it because of its slow passage of conduction.

6. What happens to the volume of air as it rises? What happens to its temperature?

AS the air rises, it expands, so the volume of air increases. As the air expands, its temperature falls.

20. Can an object be both a good absorber and a good reflector at the same time? Why or why not?

An object can never be both good absorber and a good reflector at the same time. A good absorber absorbs the radiation while a good reflector reflects the heat. Radiation absorption and reflection are opposite processes.

18. What determines whether an object us a net absorber or a net emitter if radiant energy at a given time?

An object is a net absorber of a net emitter of radiant energy at any time when its temperature is above or below that of its surroundings.

23. An object radiating energy at nigh is in contact with the relatively warm Earth. How does its conductivity affect whether or not it becomes appreciably colder than the air?

An object radiating energy at night that is in contact with the relatively warm soil, becomes colder than the air since Earth radiates more energy to deep space than it gets back.

14. How does the frequency of radiant energy relate to the absolute temperature of the radiating source?

Frequency of radiant energy is directly proportional to the absolute temperature of the radiating source.

27. In what way does glass act like one-way valve for a conventional greenhouse? Does the atmosphere play the same role?

Glass acts as a one-way gate. It allows heat of shorter wavelengths to enter into a glass room. However, glass does not allow for the longer wavelength radiation emitted by the heated objects. The atmosphere plays the same role in warming our Earth.

13. Relatively speaking, do high-frequency waves have ling wavelengths or short wavelengths?

High frequency waves have relatively short wavelengths.

22. What happens to the temperature of something that radiates energy without absorbing the same amount in return?

If an object radiates energy without absorbing the same amount in return, its temperature falls and the object feels colder.

11. Why does the direction of coastal winds change from day to night?

In the daytime, the shore warms more easily than the water; air over the shore is pushed up by cooler air that comes in from above the water to take place. At night, the process is reversed because the shore cools off more quickly than the water and then the warmer air is over the sea.

29. What is the function of a photovoltaic cell?

It converts light energy directly to electric energy at the atomic level. It absorbs photons from the incident light and release electrons.

26. What could be the consequence of completely eliminating the greenhouse effect?

It would result in the decrease of Earth's temperature and would result in Earth being covered with ice.

2. If you tough the metal sides inside of an oven with a bare hand, you're in trouble. But hold your hand briefly in the oven air and you're okay. What does this tell you about the relative conductivities of metal and air?

Metal is a good conductor of heat while air is a poor conductor. That's why the metal sides of a pizza oven are very hot compared to the air inside the oven.

25. Does Newton's law of cooling apply to warming as well as to cooling?

Newton's law of cooling is applied to both warming as well as cooling.

30. Cite three ways in which a Thermos bottle inhibits heat transfer.

No conduction, No convection, and no radiation.

12. In what form does radiant energy travel?

Radiant energy travels in the form of electromagnetic waves.

17. Since all objects emit energy to their surroundings, why don't the temperatures of all objects continuously decrease?

Since everything around us both radiates and absorbs energy continuously, the temperature of all objects remains stable and does not continuously decrease.

10. Why is Millie's hand not burned when she holds it above the escape valve of the pressure cooker?

The hot steam from the pressure cooler expands and cools down with expansion. The cooling effect of both expansion and rapid mixing with cooler air allows her to keep her hand above the escape valve of the pressure cooker without getting burned.

1. What is the role of loose electrons in heat conductors?

The loose electrons in heat conduction help in the conduction of heat by transferring energy to the neighboring electrons.

16. Cite a primary difference between waves of solar radiation and waves of terrestrial radiation.

The principal difference between the wave of solar radiation and the wave of terrestrial radiation is that the frequency and energy if solar radiation is high compared to terrestrial radiation.

21. Why dies the pupil of the eye appear black?

The pupil of an eye us a very good absorber. It absorbs all the light completely without any reflection. This is why the pupil of an eye appears black.

15. What is terrestrial radiation?

The radiation emitted by Earth is in the form of infrared waves, which are below our threshold of sight. Radiant energy emitted by Earth is called terrestrial radiation.

24. Which will undergo the greater rate of cooling- a red hot poker in a warm oven or a red hot poker in a cold room (or do both cool at the same rate)?

The rate of cooling is directly proportional to the temperature difference. So the red hot poker has a greater rate of cooling in a cold room as compared to a warm room.

4. Why are such materials as wood, fur, feathers, and even snow good insulators?

The substances like wood, fur, feather and snow are possessing good insulating properties as they contain air spaces between their molecules. This air gap or space serves as an insulator.

3. Explain why a firewalker can step quickly without harm on red-hot coals with bare feet.

We can step quickly on red-hot coals with bare feet because wood is a very good insulator. It does not conduct heat even when it is red hot.

8. How are the speeds of molecules of air affected when the air is compressed by the action of a tire pump?

When air is compressed by a tire pump, the average speed of the air molecules inside increases.

7. When an air molecule is hit by an approaching faster moving molecule, does its rebound speed increase or decrease? How about when it hits a receding molecule?

When an air molecule is hit by an approaching faster moving molecule, it rebounds with speed that is higher than its initial velocity. When it hits a receding molecule, its rebound speed is reduced.

9. How are the speeds of molecules of air affected when the air rapidly expands?

When the air expands rapidly, the average speed of molecules is reduced.