Embedded Files
General Resources:
General Resources:
Kognity Textbook: Chapter 8 (Use your ACS Login)
IB Physics Site: Topic 8 - Comprehensive notes
IB Physics Site: Topic 8 - More notes
Topic 8 Flashcards - Vocab Devo.
Conduction:
Conduction:
Thermal energy (heat) will transfer from one place to another if there is a difference in temperature. Conduction can be visualised as the result of collisions of molecules. As one end of the object is heated, the molecules there move faster. As they collide with their slow moving neighbours they transfer some of their energy. So energy is transferred by molecular collisions along the object as shown in the gif to the left.
Using the highly technical 'Heat Conduction' device to the right we were able to see that the BRASS conducted heat the fastest.
Most people have convection heaters within their house/apartment. While the heater is placed near the wall the entire room is warmed the convection of heat by the mixing of molecules.
Convection is a process where heat is transferred by the mass movement of molecules from one place to another, and often over large distances.
Liquids and gases are typically warmed by the process of convection. As the substance is heated, its density decreases causing it to rise and then is replaced by colder more dense material.
Radiation:
Radiation:
Whereas conduction and convection require matter, heat can be transferred by radiation across empty space. Radiation consists of electromagnetic waves. Radiation from the Sun for example consists of visible light plus other wavelengths that the eye cannot see including infra red radiation which is responsible for heating the Earth.
The rate at which an object radiates energy (the power) is found using the following equation known as the Stefan-Boltzmann law.
A is the surface area of the object and T is the surface temperature. The Stefan-Boltzmann constant σ is 5.67 x 10-8 W m-2 K-4. Black surfaces emit radiation best while white and shiny surfaces emit radiation least. This is represented by the emissivity e in the equation. A perfect emitter of radiation (i.e. an ideal black body) has an emissivity of 1. A poor emitter of radiation has an emissivity closer to 0.
Calculations:
An ideal black body would radiate power with an emissivity of 1.0.
Based on the temperature of each side of the Leslie cube, determine the emissivity of each side.
2. Suppose the bottom of the Leslie Cube was painted in such a way that had an emissivity of 0.54, determine the temperature that would be expected.
e - emissivity (Black Body = 1) (unitless)
𝜎 - Stefan-Boltzmann Constant (W m-2 K-4)
A - Surface area of radiating body (m2)
T - Temperature (K)
The left side is painted white, where as the right side is unpainted copper.
The left side is a 'matte' black finish, where as the right side is a 'gloss' finish paint.
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