P2 - Energy transfer by heating
- Created by: 17i.shivji
- Created on: 29-02-20 19:44
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- P2 - Energy transfer by heating
- Conduction
- Particles that are very close together can transfer heat energy as they vibrate.
- 1. When a metal is heated, the free electrons gain kinetic energy
- 2. This means that the free electrons move faster and transfer the energy through the metal
- 3. This makes heat transfer in metals very efficient
- 4. Insulators do not have free electrons and so they do not conduct heat as well as metals
- Occurs in solids only
- Why metals are good conductors?
- They have free electrons
- The outer electrons of metal atoms are not attached to any particular atom
- They are free to move between the atoms
- Insulating matters
- Energy transfer per second through a layer of insulating material depends on
- Temperature
- Thickness
- Thermal conductivity of material
- Reduce the energy transfer
- Low thermal conductivity
- Thickness of insulating material
- Energy transfer per second through a layer of insulating material depends on
- Infrared radiation
- All bodies no matter what their temperature is, emit and absorb infrared radiation
- A body at constant temperature emits and absorbs radiation at the same rate across a continuous range of wavelengths
- Radiation transmission - An object will let that radiation pass through it
- Black body radiation - Radiation emitted by a body that absorbs all radiation incident to it
- Hotter an object, the more infrared radiation it emits
- Temperature of an object increase if it absorbs more radiation than it emits
- Infrared radiation effects
- Greenhouse gases in the atmosphere absorb longer wavelength infrared radiation from the Earth
- Prevent it escaping into space
- These gases absorb radiation and emit it back to the surface
- This process makes the Earth warmer
- Greenhouse gases in the atmosphere absorb longer wavelength infrared radiation from the Earth
- Temperature and Heat
- Temperature - A measure of how hot something is
- Heat - A measure of the thermal energy contained in an object
- Specific Heat Capacity
- When heat energy is transferred to an object its temperature increase depends on
- Mass
- Material
- Amount of energy transferred
- The amount of energy needed to change the temperature of 1kg of the substance by 1 degree
- Different substances have different SHC
- When heat energy is transferred to an object its temperature increase depends on
- Insulating buildings
- Loft insulation
- Roof
- Fibreglass
- The air between the fibres helps reduce the rate of energy transfer by conduction
- Greater number of layers, thicker the insulation, the rate of energy transfer is less
- Fibreglass
- Roof
- Cavity wall insulation
- Walls
- Cavity of an outer wall - the space between the two layers of brick that make up the wall
- Insulation pumped into the cavity
- Traps the air in small pockets
- Reduces the rate of energy transfer by conduction
- Traps the air in small pockets
- Insulation pumped into the cavity
- Cavity of an outer wall - the space between the two layers of brick that make up the wall
- Walls
- Aluminium foil between radiator panel and the wall
- Reflects radiation away from the wall
- Reduces the rate of energy transfer by radiation
- Reflects radiation away from the wall
- Double-glazed windows
- Two panes with dry air or vacuum between them
- Thicker the glass, lower the thermal conductivity, slower the rate of transfer through it
- Reduces the rate of energy transfer by conduction
- Vacuum prevents energy transfer by convection
- Thicker the glass, lower the thermal conductivity, slower the rate of transfer through it
- Two panes with dry air or vacuum between them
- External walls
- Thicker bricks, lower thermal conductivity
- Rate of energy transfer of energy from inside the building - lower - cost of heating - less
- Thicker bricks, lower thermal conductivity
- Loft insulation
- Convection
- Occurs in liquids and gases
- 1. Heating a room with a radiator relies on creating convection currents in the air of the room
- 2. Energy is transferred from the radiator to the nearby air particles by conduction
- 3. The air by the radiator becomes warmer + less dense
- 4. This warm air rises and is replaced by cooler air. The cooler air is then heated by the radiator
- 5. At the same time, the previously heated air transfer energy to the surroundings. It cools becomes less dense + sinks
- 6. This cycle repeats, causing a flow of air to circulate around the room - convection current
- Conduction
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