Ch. 16 Flashcards
(6 cards)
A cup of coffee is placed on the table. Is it in thermal equilibrium?
What condition determines when the coffee is in equilibrium?
A body is said to be in thermal equilibrium, if there is no exchange of heat between the body and it’s surroundings.
The moment the coffee cup is placed on the table, it’s temperature is different from that if it’s surroundings. Hence there is transformation of heat energy from the coffee cup to the surrounding. Therefore at that moment the coffee is not in thermal equilibrium.
However, over time the temperature of the coffee will decrease until it is the same as the room temperature. At this point it will be in equilibrium, given the room stays at the same temperature.
To find the temperature at the core of the sun, you consult some websites on the internet. One site says the temperature is about 15 million C, another says it’s 15 million Kelvin l. Is this a serious discrepancy? Explain.
Temps are measure by using the temperature scale.
There is no upper limit for temperature but there is a lower limit called absolute zero. On the Celsius scale it is -273.15 degrees and on the Kelvin scale it is 0K. Since kelvin is always 273.15 degrees greater than the Celsius temperature there is no serious discrepancy in the values of temperature at the core of the sun.
Is it valid to say that a hot object contains more heat than a cold object?
No. Heat is not a quantity that one object has more of than the other.
Heat is the energy that is transferred between objects of different temperatures.
Two different objects receive the same amount of heat. Give at least two reasons why their temperature changes may not be the same.
If the objects have different masses, the object with less mass have a greater temperature change, since it has a smaller heat capacity.
Another factor is the material of the objects. The one with the smaller specific heat will have a greater temperature change.
Heat capacity is the amount of heat needed to raise the temperature of one kg of mass by one Kelvin.
Specific heat of concrete is greater than that of soil. Given this fact would you expect a major-league baseball field or the parking lot that surrounds it to cool off more in the evening following a sunny day?
The soil will cool off faster than the concrete parking lot, since it’s temperature changes more for a given amount of heat loss.
The fur of polar bears consists of hollow fibers. (Sometimes algae will grow in the hollow regions, giving the fur a green cast).
Explain why hollow fur can be beneficial to the polar bears.
The hollow fibers of hair are effective insulators because the gas within the fibers has a low thermal conductivity.
This is analogous to double-pane windows, which trap a layer of gas between the lanes for a greatly enhanced insulating effect.
