Thermal measurements and particle models
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| specific heat capacity/spəˈsɪfɪk hiːt kəˈpæsɪti/ | Nhiệt dung riêng |
| latent heat/ˈleɪtənt hiːt/ | Nhiệt ẩn |
What would explain this observation?
- Two equal masses receive the same energy but show different temperature rises. Material properties determine how energy transfer changes temperature.
Build the model
- Specific heat capacity 比热容 is energy needed to raise the temperature of unit mass by one degree.
- Specific latent heat 潜热 relates energy to change of state without temperature change for the idealized process.
- specific heat capacity: Energy per mass per temperature rise.
- latent heat: Energy associated with a change of state.
Why can temperature stay constant while a pure substance melts?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
During melting the incoming energy does work separating particles against their attractions - the latent heat - rather than raising kinetic energy, so temperature stays constant. Energy is still entering; it changes arrangement, not temperature.
Match each technical term to its precise meaning.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Temperature relates to particle motion in a model; internal energy includes kinetic and potential contributions.
- During a change of state, energy can change particle arrangements rather than temperature.
In the lab: Measure mass, electrical input and temperature change for an insulated block. Ensure the temperature sensor has good contact, allow time for equilibration, and consider energy transferred to the surroundings.
Which two habits make the investigation or model in this case more defensible?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a 0.50 kg block gains 2,000 J and rises 10 °C.
- Use E = mcΔT.
- Rearranging gives c = E/(mΔT). c = 2,000/(0.50×10) = 400 J per kilogram per degree.
- Heat loss would make the value inferred from electrical input too large.
Your turn: A 2 kg sample with c=500 J per kilogram per degree warms by 3 °C. Find energy gain.
A 2 kg sample with c=500 J per kilogram per degree warms by 3 °C. Find energy gain.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The result is 3000 J. Known: mass 2 kg; c = 500 J per kilogram per degree; temperature rise 3 degrees C. Use E = mc x temperature change. E = 2 x 500 x 3 = 3,000 J. This is the energy gained by the sample, ignoring losses.
Check the conclusion and its limits
- A flat section of a heating curve can show a phase change, not absence of energy transfer.
- Do not substitute temperature for a temperature difference in E = mcΔT.
Not true: A temperature plateau always means zero energy transfer. A plateau on a heating curve marks a phase change, where energy goes into changing particle arrangement as latent heat. Energy transfer continues; only the temperature pauses.
- Specific heat capacity is energy needed to raise the temperature of unit mass by one degree.
- Temperature relates to particle motion in a model; internal energy includes kinetic and potential contributions.
- Watch for: A flat section of a heating curve can show a phase change, not absence of energy transfer.
Write from an energy gain of 4000 J
- A 0.40 kg sample with specific heat capacity 2000 J per kilogram per degree warms by 5 degrees.
- Find the energy gain. A temperature plateau can still transfer energy.
A temperature plateau always means zero energy transfer.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
A plateau on a heating curve marks a phase change, where energy goes into changing particle arrangement as latent heat. Energy transfer continues; only the temperature pauses.
Energy per mass per temperature rise: write the technical term.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
specific heat capacity means Energy per mass per temperature rise.
A 0.40 kg sample with specific heat capacity 2000 J per kilogram per degree warms by 5 degrees. What energy does it gain, and why can a temperature plateau still mean energy transfer?
Heating energy is mass times specific heat capacity times temperature change, when the state does not change. A plateau is a different energy transfer.
What is the energy gain?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
0.40 times 2000 times 5 is 4000 J. Other options — 3000 J (the lesson sample of 2 kg warming by 3 degrees); 5 degrees (the temperature change).