Conceptual Questions: 1. Which best describes a system made up of ice, water and steam existing together in equilibrium?
a. The absolute zero phase.
b. The triple point.
c. The ice point.
d. The equilibrium point.
2. Which of the following best describes a substance in which the temperature remains constant while at the same time it is experiencing an inward heat flow?
a. It is a gas.
b. It is a liquid.
c. It is a solid.
d. It is undergoing a change of phase.
3. Which one of the following processes of heat transfer require the presence of a fluid?
a. conduction
b. radiation
c. convection
d. none of the above choices are valid
4. In a cloud formation, water vapor turns into water droplets which get bigger and bigger until it rains. This condensation will cause the temperature of the air in the clouds to:
a. get warmer.
b. get cooler.
c. will not affect the temperature of the air in the clouds.
d. there is no air in clouds.
5. Why are cloudy nights generally warmer than clear ones?
6. How does the "greenhouse effect" work?
Numerical Problems: answers link to a help page.
1. A 10 g piece of aluminum (which has a specific heat of 0.215 cal/gm*øK) is warmed so that its temperature increases by 5Kø. How much heat was transferred into it?
2. An inventor develops a stationary cycling device by which an individual can convert all of the pedaling energy into heat for warming water. How much mechanical energy is required to increase the temperature of 300 gm of water (enough for 1 cup of coffee!) from 20øC to 95øC? (1 cal = 4.186 J)
3. A 0.003 kg lead bullet is traveling at a speed of 240 m/s when it embeds in a wood post. If we assume that half of the resultant heat energy generated remains with the bullet, what is the increase in temperature of the bullet? (specific heat of lead = 30 cal/kg*Cø)
4. A puddle holds 150 gm of water. If 0.50 gm of water evaporates from the surface, what is the approximate temperature change of the remaining water? (Lv = 540 cal/gm)
5. Iced tea is made by adding ice to 1.8 kg of hot tea, initially at 80øC. How many kg of ice, initially at 0øC, are required to bring the mixture to 10øC? (Lf = 80 kcal/kg)
6. What is the temperature increase of 4.0 kg of water when heated by an 800 W immersion heater for 10 min?
7. On a cold winter day, the air temperature outside might be 30øK lower than inside. Most window glass is about 2mm thick. If there is only one layer of glass, is most of the energy transfer in radiation or in conduction? The conductivity of glass is 0.8 J s-1 m-1 øK-1 and the emissivity in the infrared is about 0.8. Hint: assume only one is important, and then the other. Which ever results in the greater heat transfer is the most important.