Which of the following statatements is correct?
a. Thermos bottles keep food warm by combating heat loss through convection.
b. A thick quilt is an example of an isulator with a low R value
c. An object that is cool to the touch at room temperature is a poor conductor of heat
d. Wearing a white shirt on a hot, sunny day keeps you cool because it emits more solar energy than a darker shirt
e. All of th above statements a-d are all correct
f. None of the above statements a-d are all incorrect
To determine which of the statements is correct, we'll evaluate each statement individually:
a. Thermos bottles keep food warm by combating heat loss through convection.
To verify this statement, we need to understand how a thermos bottle works. Thermos bottles are designed to minimize heat transfer through all three modes: conduction, convection, and radiation. However, they are especially effective at reducing convection, as they have a double-walled construction with a vacuum in between. This vacuum acts as an insulator, preventing heat transfer through convection. Thus, the statement is correct.
b. A thick quilt is an example of an insulator with a low R-value.
R-value is a measure of thermal resistance, with higher values indicating better insulation. Since the statement suggests that a thick quilt has a low R-value, it implies that the quilt is not a good insulator. This contradicts the usual understanding that thicker insulation provides better thermal resistance. Therefore, the statement is incorrect.
c. An object that is cool to the touch at room temperature is a poor conductor of heat.
To verify this statement, we need to understand the concept of thermal conductivity. If an object feels cool to the touch, it means that it is not actively transferring heat to your skin, indicating low thermal conductivity. Therefore, the statement is correct.
d. Wearing a white shirt on a hot, sunny day keeps you cool because it emits more solar energy than a darker shirt.
This statement implies that a white shirt emits more solar energy than a darker shirt, which would help in keeping the wearer cool. However, in reality, the color of the shirt affects its absorption and reflection of solar energy. Darker colors tend to absorb more energy, while lighter colors reflect more. Therefore, a darker shirt would absorb more solar energy and might make the wearer feel hotter. Thus, the statement is incorrect.
To summarize:
- Statement a is correct.
- Statement b is incorrect.
- Statement c is correct.
- Statement d is incorrect.
Based on this analysis, the correct answer is f. None of the above statements a-d are all correct.