Physics unit 1

Heat-

Heat energy is transferred via conduction, convection and radiation.

Infrared radiation is the emission of electromagnetic waves and all objects continually emit and absorb it. Hotter objects emit more radiation and cooler ones absorb more. Dark, matte surfaces absorb and emit more radiation whilst shiny and light surfaces reflect them 

Conduction of heat energy is the process where vibrating particles pass extra kinetic energy to neighbouring particles. Conduction occurs faster in dense solids and solids with spaces in-between make better insulators. Metals are good conductors due to the delocalised electrons which transfer energy to other electrons.

Convection occurs when the more energetic particles move from the hotter region to the cooler one. 

The immersion heater: heat energy is transferred from the heater coils to the water via conduction and the water near the coils gain energy causing them to spread and making the water here less dense. The hotter water rises above the cooler water pushing the cooler water down and the process repeats creating a convection current that circulates the heat energy through water. -- Convection currents are basically all about changes in density.

Condensation is when gasses cool causing particles to loose kinetic energy pulling them close together until it reaches a liquid state. The rate of condensation will be faster if the:

·         temperature of gas is lower

·         surface that the gas touches is lower

·         density is higher as few particles with have the energy to break their bonds to remain a gas

·         airflow is less as concentration of particles will be higher increasing the rate of condensation

Evaporation is facilitated if particles are travelling in the right direction and fast enough to overcome attractive forces of the other particles in the liquid. The particles with the most energy evaporate from the liquid causing the average speed and kinetic energy of the liquid to decrease, and this decrease in energy means the remaining liquid particles become cooler. The rate of evaporation will be faster if the:

·         temperature is higher as the particles with have more energy

·         density is lower as it takes less energy to break the bonds

·         surface area is larger as enough particles will be near the surface of the liquid

·         airflow is greater as the concentration will be lower

The rate of heat energy transfer is affected by:

·         since energy is radiated from the surface, the larger the surface area the more infrared waves can be emitted so the quicker the transfer of heat

·         if two objects have the same surface area but different volumes the object with the smaller volume will cool quickest as it has a higher proportion of the object in contact with the surroundings

·         the material, good conductors transfer heat quicker than insulators

Energy efficiency-

Payback time = initial cost/annual saving

Cavity wall insulation= foam in wall stopping convection currents being made in the gaps between walls and…