Distinguish temperature from heat transfer and classify transfer mechanisms.
Method and worked examples
Temperature relates to average particle kinetic energy; internal energy also depends on the amount and type of matter. Heat is energy transferred from hotter to colder systems because of their temperature difference. Thermal equilibrium means equal temperature and no net heat transfer. Convert T(K)=θ(∘C)+273.15 and θ(∘F)=1.8θ(∘C)+32. Absolute zero is 0K.
Conduction transfers energy microscopically without bulk flow; convection transports it with fluid motion; radiation is electromagnetic and needs no medium. Most materials expand when heated. Expansion gaps accommodate bridge movement and liquid expansion can indicate temperature. A temperature change has equal numerical size in kelvin and degrees Celsius, unlike their absolute readings.
Example 1
Convert 25.0∘C to kelvin.
T=25.0+273.15=298.15K, or 298.2K to one decimal place.
Example 2
A solid spoon warms along its length while in hot water. Classify that transfer along the spoon.
Conduction: microscopic interactions transfer energy through the solid without the spoon material flowing along its length.
Watch out:An object has internal energy. Heat describes energy crossing a system boundary due to a temperature difference.
13. Temperature, thermal energy and transfer | Year 11 Physics | Ascent Arcade