﻿ Lecture 35 Summary
• Thermal expansion
• Specific Heat
• Thermal energy

• Heat flow and thermal energy
Example #1
Example #2
Example #3

• Heat transfer
 COLD Turbulent motion of glycerol in a container heated from below and cooled from above. The bright lines show regions of rapid temperature variation. The fluid contains many "plumes," especially near the walls. The plumes can be identified as mushroom-shaped objects with heat flowing through the "stalk" and spreading in the "cap." The hot plumes tend to rise with their caps on top; falling, cold plumes are cap-down. All this plume activity is carried along in an overall counterclockwise "wind" caused by convection. Note the thermometer coming down from the top of the cell. Figure adapted from J. Zhang, S. Childress, A. Libchaber, Phys. Fluids 9, 1034 (1997). See detailed discussion in Kadanoff, L. P., Physics Today 54, 34 (August 2001). HOT

Walker4e
Reading quiz The two blocks shown below were heated to the same temperature and placed on paraffin wax. The fact that they melted different amounts of wax is a consequence of the different ______ of the two materials.
A. emissivity
B. thermal conductivity
C. specific heat
D. latent heat of fusion

sj6 20.13
If a 6.00 m2 solar heater collects 550 W/m2, how much time to heat 0.189 m3 (50 gal) of water from 20°C to 60°C?
A. 3.10 min
B. 9.17 min
C. 2.66 h
D. 2.5 days

klm
You stir some juice with a force of 20 N for a total distance of 30 m. How much heat have you transferred?
A. 143 cal
B. 300 cal
C. 600 cal
D. 2510 cal

klm
If the mass of the juice is 2 kg, what is the temperature change of the juice? Use the specific heat of water.
A. 0.014°C
B. 14°C
C. 0.072°C
D. 71.7 °C

gc6 14.q27
A piece of wood lying in the Sun absorbs more heat than a piece of shiny steel. Why doesn't the wood feel hotter than the steel?
A. The wood has a smaller specific heat.
B. The wood has a lower temperature.
C. The wood has a smaller thermal conductivity.
D. The wood is less dense than steel.

gc6 14.37
Two rooms share an 16.0 m², 12 cm thick brick wall. How many 100 W light bulbs are required to maintain a 20°C temperature difference across the wall?
A. 69
B. 46
C. 23
D. 12

gc6 14.q19
The temperature of land changes quicker than nearby water. Therefore convective "sea breezes" blow ____ during the day and _____ during the night.
A. onshore ... onshore
B. onshore ... offshore
C. offshore ... onshore
D. offshore ... offshore

gc6 14.q28
Why does the Earth cool more quickly on clear nights than on cloudy nights?
A. Clouds reradiate energy back to Earth.
B. Clouds prevent thermal conduction like a blanket.
C. Clouds promote thermal convection.
D. Clouds contain latent heat energy.

sj6 20.49
If a 0.250 mm2 filament with e = 0.950 radiates 2.00 W of light, what is its temperature?
A. 2000 K
B. 2850 K
C. 3490 K
D. 3683 K

D. specific heat

Aluminum has a specific heat that is seven times greater than that of lead. This means the aluminum stores more thermal energy, energy that is available to melt a larger quantity of paraffin wax.

C. 2.66 h

A. 143 cal

C. 0.072°C

C. The wood has a smaller thermal conductivity.

Although it has the about the same temperature, or even higher than the steel, it feels cooler because heat flows less quickly from the wood to your skin.

C. 23

B. onshore ... offshore

A. Clouds reradiate energy back to Earth.

The Earth cools primarily by radiation. The clouds absorb energy from the radiating Earth, and reradiate some of it back to the Earth, reducing the net amount of radiant energy loss.

C. 3490 K