P2 Energy Transfer By Heating Flashcards
Heat transfers-Kinetic theory explain 3 states of matter
Solids- strong forces of attraction hold the particles close together in a fixed, regular arrangement. The particles don’t have much energy so they can only vibrate about their fixed position.
Liquids- there are weaker forces of attraction between the particles. The particles are close together, but can move past each other, and form irregular arrangements. They have more energy than the particles in a solid-move in random direvtions.
Gases-there are almost no forces of attraction between the particles. The particles have more energy than those in liquids and solids-free to move and travel in random directions at high speeds
Conduction of heat
Conduction of heat is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
In solid, the particles are tightly packed together un a fixed position. The particles are close together in a fixed position vibrating. As the solid is heated,thermal energy is transferred into kinetic energy in the particles. The particles vibrate faster. The energy/vibrations are passed on from particle to another. Heat spreads through solid.
Metals are good conductors-why?
Metals conduct so well because the electrons are free to move inside the metal. At the hot end the electrons move faster and collide with other free electrons,transferring energy. Because the electrons can move freely this is obviously a much faster way of transferring the energy through the metal than slowly passing it between jostling neighbouring atoms.
Convection
Convection occurs when the more energetic particles move from the hotter region to the vooler region and take their heat energy with them.
1)heat energy is transferred from the heater coils to the water by conduction (particle collisions)
2) the particles near the coils get more energy,so they start moving around faster
3) this means there’s more distance between them i.e the water expands and becomes less dense
4) this reduction in density means that the hotter water tends to rise above the denser,cooler water
5) as the hot water rises it displaces the colder water out of the way,making it sink towards the heater coils
6) this cold water is then heated by the coils and rises-and so it goes on.
Conduction of heat-notes
Thermal conduction is the process where kinetic energy is transferred by vibrating particles in a substance
-the vibrating particles transfer energy from the kinetic store to kinetic store of neighbouring particles
-the direction of energy transfers is always from hot to cold
-the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material
-materials with high thermal conductivity heat up faster than materials with low thermal condcutivity
Defenition of thermal conductivity
The ability of material to allow the flow of heat
Examples of substances with high and low thermal condcutivity
High:
-diamond
-aluminium
-graphite
Low:
-air
-steel
-bronze
Factors affecting conduction-notes
- an insulator is a substance that is an poor thermal conductor
E.g wool,plastic,wood
-insulators are used to reduce energy transfers,for example, to keep a house warm or build a soundproof room
the energy transfer through a layer of insulating depends on:
-the temperature across the material-the greater the temperature difference the more conduction
-thickness of material-thicker the material, less energy will be transferred by condcution
-thermal conductivity of material- higher thermal conductivity, more energy will be transferred by conduction
therefore good insulators which keep the energy transfer through them as low as possible have:
-a low thermal conductivity
-layers that are as thick as possible
Specific heat capacity notes
The specific heat capacity of a substance is the energy needed to raise the temperature of 1kg of the substance by 1 degrees.
-if a substance has a low specific heat capacity, it heats up and cools down quickly as it takes less energy to change its temperature.
-if a substance has a high specific heat capacity,it heats up and cools down slowly so it takes more energy to change its temperature
Low v high heat capacity
Specific heat capacity is mainly used for solid and liquids.
- good electrical conductors, such as copper and lead, are excellent thermal conductors due to their low specific heat capacity.
-water has a very high specific heat capacity,making it ideal for heating homes as the water remains hot in a radiator for a long time
Formula for specific heat capacity
Energy= mass x specific heat capacity x temperature change
^E=mc^ø
E= joules
M= kilograms
C= j/kg*c
Ø= degrees celsius
Heating and insulating buildings
-electric or gas heaters and gas or oil-fired central heating or solid-fuel stoves are used to heat houses
-loft insulation such as fibreglass reduces the rate of energy transfer through the roof. Fibreglass is a good insulator. The air between the fibres also helps reduce the rate of energy transfer by conduction. The greater number of layers insulation,the thicker the insulation will be. So the rate of energy transfer through the roof will be less
-cavity wall insulation- foam squirted into the gap between the bricks stops convection currents being set up in the gap and radiation across the gap. The insulating foam and the air pockets trapped in it also helps reduce heat loss by conduction
Aluminium foil between the radiator panel and the wall reflects radiation away from the wall and so reduces the rate of energy transfer by radiation.
Double-glazed windows have 2 glass panes with dry air or vacuum between the panes. The thicker the glass and the lower its thermal conductivity is, the slower the rate if transfer of energy through it by conduction will be. Dry air is a good insulator, so it reduces the rate of energy transfer by conduction. A vacuum also prevents energy transfer by convection
