P1 Flashcards
Explain what conduction is
Conduction is the main form of heat transfer in solids, conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
Explain what radiation is
Heat radiation is the transfer of heat energy by infrared (IR) radiation. All objects are continually emitting and absorbing infrared radiation, it is emitted from the surface of an object. An object thats hotter than its surroundings emits more radiation than it absorbs (as it cools down). An object thats cooler than its surroundings absorbs more radiation than it emits (as it warms up).
Describe how and why different surfaces affect radiation
Dark, matt surfaces absorb infrared radiation much better than light, shiny surfaces, such as gloss white or silver. They also emit much more infrared radiation (at any given temprature) light shiny surfaces reflect radiation which is why they are used in the inside of flasks to keep hot/cool air in/out of it
Describe the structure of a solid
Solids have strong forces of attraction to hold the particles close together in a fixed, regular arrangement. The particles only have enough energy to vibrate in their fixed positions
Describe the structure of a liquid
Liquids have 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 of a solid so can move in random directions at low speed
Describe the structure of gases
There are almost no forces of attraction between the particles. The particles have more energy than those in liquids and solids, they are free to move and travel in random directions in high speed
Why are metals such good conductors?
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. These other electrons then pass on their energy to other electrons etc.Because the other electrons can move freely this is obviously a much faster way of transferring energy.
What is the radiator example of convection?
Heating a room with a radiator relies on convection currents too. Hot, less dense released by the radiator rises and denser, cooler air flows to replace it, it then gets hot and then rises and replaces the what was hot air which has cooled down
What is condensation?
When a gas cools the particles slow down and lose kinetic energy. The attractive forces between the particles pull them closer together. If the temperature gets cold enough and the gas particles get close enough together that condensation can take place, the gas becomes a liquid. Water vapour in the air condenses when it comes in contact with a cold surface, eg drinks glases
Explain what convection is
Convection is the main form of heat transfer in liquids and gases it occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.
Explain what evaporation is
Evaporation is when particles escape from a liquid. They can evaporate from a liquid at temperatures that are much higher than the liquids boiling point, the fastest particles with the most kinetic energy are most likely to evaporate from the liquid so when they do, the average speed and kinetic energy of the remaining particles decreases. This decrease in average particle energy means the temprature of the remaining liquid falls, this is called the cooling effect, it can be very useful when your sweating your sweat evaporates and cools you down.
What ways do humans have of controlling heat transfer?
In the cold hairs on your skin stand up to trap a thick layer of insulating air around the body. This limits the amount of heat loss by convection. Some animals do the same with fur. When your too warm, your body diverts more blood to flow near the surface of your skin so that more heat can be lost by radiation, this limits the amount of heat loss by convection.
What ways do animals have of controlling body temperature?
Generally in warmer climates, animals have larger ears than those in colder climates to help control heat transfer. For example, arctic foxes have evolves small ears, with a small surface area to minimise heat loss by radiation and conserve body heat. Desert foxes on the other hand have huge ears with a large surface area to allow them to lose heat by radiation and easily keep cool.
what is payback time
initial cost over annual savings
what is 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
what is loft insulation
a thick layer of fibreglass wool laid our across the whole loft floor, reduces conduction and radiation
what is fraught proofing
strips of foam and plastic around doors and windows stop draughts they reduce heat loss due to convection
what is hot Walter tank jacket
fibreglass wool, reduces conduction and radiation
what are thick curtains
big bits of cloth over the window to reduce heat loss by conduction and radiation
what is. a specific heat capacitors
it takes heat energy to increase the temperature of some materials than others. it tells you how much energy things can store. material which need to gain a lot of energy to warm up also release loads of energy when they cool down. they can store a lot of heat. it is the amount of energy needed to ease the temperature of 1 kg of a substance by 1oC
what is the formula for specific heat capacity
e energy transferred = m mass X c specific heat capacity X Greek o temperature change
triangle of specific heat capacity
e
mco
name some properties heaters have
the materials used in heaters usuailly have high specific heat. capacities so. to store a high amount of heat energy.
water has a very high SHC it is also a liquid so can be pumped easily around which is why it is ideal for central heating systems in buildings
some heaters are filled with oil which has a specific heat capacity of around 2000 j/kg oC this is. lower than waters but has a higher boiling point than water so can be safely heated to a higher point
tell me about the cheeky 9 types of energy
electrical energy, whenever a current flows
light energy, from the sun light bulbs etc
sound energy, from loudspeakers or anything noisy
kinetic energy, anything that’s moving has it
nuclear energy, released from only nuclear reactions
thermal energy, flows from hotter objects to cooler ones
gravitational potential energy, powered by anything which can fall
elastic potential, stretched springs rubber bands elastic etc
chemical energy, processed by foods fuels batteries etc
what is the conversion of energy principle
energy can be transferred usefully from one form to another. stored of dissipated but it can never be created or destroyed
what makes energy useful
if it’s able to be converted from one form to another
how do you calculate energy efficiency
useful NRG in over total NRG out
nandos
