P1 Energy and Heat Transfer
- Created by: Hollie Wickens
- Created on: 30-03-14 10:05
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- Energy and Heat transfer
- Heat radiation
- Heat energy flows away from a hotter object to its cooler surroundings
- Heat is transferred in three different ways - radiation, conduction or convection
- Heat radiation is the transfer of heat energy by infrared radiation
- Infrared radiation can be emitted by solids, liquids and gases
- Any object can both emit and absorb infrared radiation, whether or not conduction and convection are also taking place
- Heat radiation is the transfer of heat energy by infrared radiation
- Infrared radiation can be emitted by solids, liquids and gases
- Any object can both emit and absorb infrared radiation, whether or not conduction and convection are also taking place
- Any object can both emit and absorb infrared radiation, whether or not conduction and convection are also taking place
- All objects are continually emitting and absorbing infrared radiation
- Infrared radiation is emitted from the surface of an object
- An object that's hotter than its surroundings emits more radiation than it absorbs (as it cools down)
- An object that's cooler than its surroundings absorbs more radiation than it emits (as it warms up)
- Radiation depends on surface colour and texture
- Dark, matt surfaces absorb infrared radiation falling on them much better than light, shiny surfaces, such as gloss white or silver
- They also emit much more infrared radiation (at any given temperature)
- Light, shiny surfaces reflect a lot of the infrared radiation falling on them
- Solar hot water panels contain water pipes under a black surface
- Radiation from the Sun is absorbed by the black surface to heat the water in the pipes
- This water can be used for washing or pumped to radiators to heat the building
- Radiation from the Sun is absorbed by the black surface to heat the water in the pipes
- Dark, matt surfaces absorb infrared radiation falling on them much better than light, shiny surfaces, such as gloss white or silver
- The hotter an object is, the more radiation it radiates in a given time
- Infrared radiation is emitted from the surface of an object
- Infrared radiation can be emitted by solids, liquids and gases
- Heat radiation is the transfer of heat energy by infrared radiation
- Any object can both emit and absorb infrared radiation, whether or not conduction and convection are also taking place
- All objects are continually emitting and absorbing infrared radiation
- Infrared radiation is emitted from the surface of an object
- An object that's hotter than its surroundings emits more radiation than it absorbs (as it cools down)
- An object that's cooler than its surroundings absorbs more radiation than it emits (as it warms up)
- Radiation depends on surface colour and texture
- Dark, matt surfaces absorb infrared radiation falling on them much better than light, shiny surfaces, such as gloss white or silver
- They also emit much more infrared radiation (at any given temperature)
- Light, shiny surfaces reflect a lot of the infrared radiation falling on them
- Solar hot water panels contain water pipes under a black surface
- Radiation from the Sun is absorbed by the black surface to heat the water in the pipes
- This water can be used for washing or pumped to radiators to heat the building
- Radiation from the Sun is absorbed by the black surface to heat the water in the pipes
- Dark, matt surfaces absorb infrared radiation falling on them much better than light, shiny surfaces, such as gloss white or silver
- The hotter an object is, the more radiation it radiates in a given time
- Infrared radiation is emitted from the surface of an object
- Infrared radiation can be emitted by solids, liquids and gases
- Conduction and convection involve the transfer of energy by particles
- 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
- This process continues throughout the solid and gradually some of the extra kinetic energy (or heat) is passed all the way through the solid, causing a rise in temperature at the other side of the solid
- Usually conduction is faster in denser solids, because the particles are closer together and so will collide more often and pass energy between them
- Materials that have larger spaces between their particles conduct heat energy much more slowly - these materials are insulators
- Metals are good conductors because of their free electrons
- At the hot end the electrons move faster and collide with other free electrons, transferring energy. These other electrons then pass on their extra energy to other electrons, etc.
- Because the electrons can more freely, this is obviously a much faster way of transferring the energy through the metal than slowly passing it between jostling neighbouring atoms
- Conduction is more efficient through a short, fat rod than through a long, thin rod. It all comes down to how far the electrons have to transfer the energy
- Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles
- Convection is the main form of heat transfer in liquids and gases
- Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them
- This is how immersion heaters in kettles and hot water tanks and convection heaters work
- Immersion heaters
- Heat energy is transferred from the heater coils to the water by conduction
- The particles near the coils get more energy, so they start moving around faster
- This means there's more distance between them, i.e. the water expands and becomes less dense
- This reduction in density means that the hotter water tends to rise above the denser, cooler water
- As the hot water rises it displaces the colder water out of the way, making it sink towards the heater coils
- This cold water is then heated by the coils and rises - and so it goes on
- You end up with convection currents going up, round and down, circulating the heat energy through the water
- This cold water is then heated by the coils and rises - and so it goes on
- As the hot water rises it displaces the colder water out of the way, making it sink towards the heater coils
- This reduction in density means that the hotter water tends to rise above the denser, cooler water
- This means there's more distance between them, i.e. the water expands and becomes less dense
- The particles near the coils get more energy, so they start moving around faster
- Heat energy is transferred from the heater coils to the water by conduction
- Immersion heaters
- Convection currents are all about changes in density
- This is how immersion heaters in kettles and hot water tanks and convection heaters work
- Convection can't happen in solids because the particles can't move
- Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them
- This is how immersion heaters in kettles and hot water tanks and convection heaters work
- Immersion heaters
- Heat energy is transferred from the heater coils to the water by conduction
- The particles near the coils get more energy, so they start moving around faster
- This means there's more distance between them, i.e. the water expands and becomes less dense
- This reduction in density means that the hotter water tends to rise above the denser, cooler water
- As the hot water rises it displaces the colder water out of the way, making it sink towards the heater coils
- This cold water is then heated by the coils and rises - and so it goes on
- You end up with convection currents going up, round and down, circulating the heat energy through the water
- This cold water is then heated by the coils and rises - and so it goes on
- As the hot water rises it displaces the colder water out of the way, making it sink towards the heater coils
- This reduction in density means that the hotter water tends to rise above the denser, cooler water
- This means there's more distance between them, i.e. the water expands and becomes less dense
- The particles near the coils get more energy, so they start moving around faster
- Heat energy is transferred from the heater coils to the water by conduction
- Immersion heaters
- Convection currents are all about changes in density
- This is how immersion heaters in kettles and hot water tanks and convection heaters work
- Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them
- Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them
- Conduction is the main form of heat transfer in solids
- Heat radiation is the transfer of heat energy by infrared radiation
- Heat is transferred in three different ways - radiation, conduction or convection
- Heat energy flows away from a hotter object to its cooler surroundings
- Condensation and Evaporation
- Condensation is when gas turns to liquid
- When a gas cools, the particles in the gas 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
- The attractive forces between the particles pull them closer together
- Water vapour in the air condenses when it comes into contact with cold surfaces, e.g. drinks glasses
- The steam you see rising from a boiling kettle is actually invisible water vapour condensing to form tiny water droplets as it spreads into cooler air
- The rate of condensation will be faster if the:
- Temperature of the gas is lower
- The average particle energy in the gas is lower - so more particles will slow down enough to clump together and form liquid droplets
- Airflow is less
- The concentration of the substance in the air will be higher, and so the rate of condensation will be greater
- Density is higher
- The forces between the particles will be stronger
- Fewer particles will have enough energy to overcome these forces and will instead clump together and form a liquid
- The forces between the particles will be stronger
- Temperature of the surface the gas touches is lower
- Temperature of the gas is lower
- When a gas cools, the particles in the gas slow down and lose kinetic energy
- Evaporation is when liquid turns to gas
- Evaporation is when particles escape from a liquid
- Particles can evaporate from a liquid at temperatures that are much lower than the liquid's boiling point
- Particles near the surface of a liquid can escape and become gas particles if:
- The particles are travelling in the right direction to escape the liquid
- The particles are travelling fast enough (they have enough kinetic energy) to overcome the attractive forces of the other particles in the liquid
- The rate of evaporation will be faster if the:
- Temperature is higher
- At higher temperatures, the average particle energy will be higher, so more particles will have enough energy to escape
- Density is lower
- The forces between the particles will usually be weaker, so more particles will have enough energy to overcome these forces and escape the liquid
- Surface area is larger
- More particles will be near enough to the surface to escape the liquid
- Airflow over the liquid is greater
- The lower the concentration of an evaporating substance in the air it's evaporating into, the higher the rate of evaporation
- A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower
- Airflow over the liquid is greater
- The lower the concentration of an evaporating substance in the air it's evaporating into, the higher the rate of evaporation
- A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower
- A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower
- The lower the concentration of an evaporating substance in the air it's evaporating into, the higher the rate of evaporation
- Airflow over the liquid is greater
- A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower
- The lower the concentration of an evaporating substance in the air it's evaporating into, the higher the rate of evaporation
- Temperature is higher
- Evaporation is when particles escape from a liquid
- Condensation is when gas turns to liquid
- Factors that affect the rate of heat transfer
- Type of material
- Objects made from good conductors transfer heat away more quickly than insulating materials
- If an object is in contact with a conductor, the heat will be conducted away much faster than if it is in contact with an insulator
- Surface area and volume
- Heat energy is radiated from the surface of an object
- The bigger the surface area, the more infrared waves that can be emitted from (or absorbed by) the surface - so the quicker the transfer of heat
- For example, radiators have large surface areas to maximise the amount of heat they transfer
- This is why car and motorbike engines often have 'fins' - they increase the surface area so heat is radiated away quicker, meaning the engine cools quicker
- Heat sinks are devices designed to transfer heat away from objects they're in contact with, for example computer components
- They have fins and a large surface area so they can emit heat as quickly as possible
- The bigger the surface area, the more infrared waves that can be emitted from (or absorbed by) the surface - so the quicker the transfer of heat
- If two objects at the same temperature have the same surface area but different volumes, the object with the smaller volume will cool more quickly
- This is because a higher proportion of the object will be in contact with its surroundings
- Heat energy is radiated from the surface of an object
- Type of material
- Heat radiation
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