Unit 18: Temperature and Heat
Temperature scales, thermal expansion, specific heat, and the latent heat hiding inside a phase change.
6 topics · 19 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Temperature and Thermal Equilibrium
- How it worksHow does the zeroth law of thermodynamics let a thermometer measure temperature at all?
- Worked exampleFind the equilibrium temperature when 1 kg of water at 80 degrees C is mixed with 1 kg of water at 20 degrees C.
- Common mistakeWhy doesn't a material feeling colder to the touch always mean it actually has a lower temperature?
- Going furtherWhat happens to two objects at different temperatures placed in contact and left alone long enough?
Your turn1 of 2
2.24 kg of water at 79 degrees C is mixed with 2.24 kg of water at 38 degrees C. What is the equilibrium temperature, in degrees C?Temperature Scales and Thermometers
- How it worksHow does a thermometer's physical property, like the expansion of mercury, get calibrated into a temperature reading?
- Worked exampleFind the Kelvin and Fahrenheit equivalents of a temperature of 37 degrees Celsius.
- Common mistakeWhy doesn't a negative Celsius temperature mean an object has negative thermal energy?
Your turn1 of 2
Convert 64 degrees Celsius to Kelvin.Thermal Expansion
- How it worksHow does heating a material increase the average spacing between its vibrating atoms?
- Worked exampleFind the increase in length of a 10 m steel beam heated by 40 degrees C, given a linear expansion coefficient of 1.2e-5 per degree C.
- Common mistakeWhy doesn't every material expand by the same amount for the same rise in temperature?
Your turn1 of 2
A steel beam of length L is heated by a temperature change dT, with a linear expansion coefficient alpha. Write an expression, in terms of alpha, L, and dT, for the increase in its length.Heat, Specific Heat, and Calorimetry
- How it worksHow does specific heat determine how much a given mass's temperature rises for each joule of heat added?
- Worked exampleFind the heat needed to raise the temperature of 2 kg of water by 15 degrees C, using specific heat 4186 J/(kg C).
- Common mistakeWhy isn't heat the same thing as temperature, even though adding heat usually raises an object's temperature?
Your turn1 of 2
Write an expression, in terms of m, c, and dT, for the heat needed to raise the temperature of a mass m of a substance with specific heat c by an amount dT.Phase Changes and Latent Heat
- How it worksHow does latent heat go entirely into breaking molecular bonds during a phase change instead of raising temperature?
- Worked exampleFind the heat needed to melt 0.5 kg of ice at 0 degrees C, using a latent heat of fusion of 334000 J/kg.
- Common mistakeWhy doesn't boiling water get any hotter no matter how high you turn up the stove underneath it?
Your turn1 of 2
Write an expression, in terms of m and Lf, for the heat needed to melt a mass m of ice with latent heat of fusion Lf.Mechanisms of Heat Transfer
- How it worksHow do conduction, convection, and radiation each move heat by a completely different physical process?
- Worked exampleFind the rate of heat conduction through a 2 m2 window 0.005 m thick with thermal conductivity 0.8 W/(m C) across a 20 degree C difference.
- Ties togetherHow does radiative heat transfer let the Sun warm the Earth across the vacuum of space where conduction and convection can't work?
Your turn1 of 2
A window has area 3 square meters and thickness 8 mm, with thermal conductivity 0.8 W/(m C). What is the rate of heat conduction through it, in watts, across a temperature difference of 28 degrees C?