Kinetic theory explains the movement of particles in comparison with each state of matter.
In a solid, liquid and gas each contain the same particles; however these particles are arranged differently depending of their energy levels. The more energy a particle has the weaker the forces of attraction between the particles: a gas' particles have more energy than solids' thus they can move freely at a fast pace.
Solids - strong electromagnetic forces, close and fixed/regular arrangement of particles so the particles have such little energy that they can only vibrate in their fixed positions.
Liquids - weaker intermolecular forces between particles than in a solid, more energy, irregular arrangement, particles moving over each other at low speeds.
Gases - almost no forces of attraction, high energy levels, free to move in random diretions at high speeds.
Radiation is one of the three ways in which heat can be transfered.
Infrared radiation is the emmision of electromagnetic waves.
All objects are emitting and absorbing infrared radiation. If an object is cooler than its surroundings then it will absorb more radiation than it emits to warm up. Whereas an object thats hotter than its surrounding then it wil emit more radiation than it absobs to cool down.
The cooler/hotter an object is the more radiation that is absobed/emitted.
An example of heat radiation is the heat emitted by a fire which can be felt in the air around it.
Dark, matt surfaces absorb infrared radiation better than light, shiny surfaces; as well as emitting more infrared radiation. This is because light, shiny surfaces reflect a lot of the infrared radiation falling on them.
Example: Solar pannels have black pipes under the glass to absorb more of the sun's radiation for a higher energy intake.
Conduction of heat energy is when vibrating particles pass on their extra energy to neighbouring particles.
Conduction occurs better in dense solids as the particles are more tightly packed so they will collide more often - so more energy is transfered. Materials with wide spaces between the paticles conduct poorly: these are called insulators.
Metals are good conductors due to their free electrons. So electrons at the hot end of the metal move quicker and collide with other free electrons, which transfers energy. Thus metals are good conductors as they can transfer heat energy rapidly with their free electrons colliding in comparison to transfering energy slowly via neighbouring particles.
Efficiency of conduction is better in short, fat rods than long, thin rods as the electrons have a smaller distance to travel.
Convection occurs in gases and liquids, when particles with more energy move from the hotter region to the cooler region and take their heat energy with them.
- Heat is transfered from the source of thermal energy by conduction
- The particles surrounding the heat source conduct more energy and begin to move faster
- They gain a larger distance between them so they become less dense
- The less dense (hotter) water/air rises above the more dense cooler water/air
- The warmer risen particles displaces the colder particles causing them to sink
- This displaced water/air is then heated by the energy source and rises
- Convection currents are caused by this cycle, circulating heat energy through water/air
Convection currents are most efficient in round/ square containers are they allow the current to flow better than shallow/ tall containers
Radiators heating the air in a room and immersion heaters heating water in the tank are both examples of practicle use of convection currents. Additionally the mantle below the earth's crust has convection currents in it from the heat of the earth's core; causing the tectonic plates to move.