Energy Transfer by Heating - P1 Unit 1
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- Created on: 08-03-14 15:25
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- Energy Transfer by Heating - P1 Unit 1.1 - 1.6
- Infrared Radiation
- All objects emit infrared radiation
- The hotter the object the more it emits in a given time
- It is energy transfer by electromagnetic waves
- (It's part of the electromagnetic spectrum)
- We can detect it with our skin as heat
- It can travel through a vacuum
- How we get energy from the sun
- All objects emit infrared radiation
- Surfaces and Radiation
- Dark Matt surfaces
- Good absorbers of infrared radiation
- Will become hotter than a white shiny surface
- Good emitters of infrared radiation
- Will cool down quicker than a shiny white object
- Good absorbers of infrared radiation
- Light Shiny Surfaces
- Good reflectors of infrared radiation
- Dark Matt surfaces
- States of Matter
- Three states of matter
- Solid
- Particles vibrate in fixed positions, has a fixed shape
- Liquid
- Particles in contact with each other, move at random, no fixed shape and can flow
- Gas
- Particles far apart, move at random faster, no fixed shape and can flow
- Low density compared to solid or liquid
- Solid
- Properties used to describe state of matter are: Flow, shape and volume
- Three states of matter
- Conduction
- Conduction occurs mainly in solids
- When heated, particles gain kinetic energy and vibrate more.
- Metals are good conductors
- They have free electrons which gain kinetic energy and move through the metal, colliding with other particles and passing on the energy
- Opposite of conductor is insulator
- Examples are wool and fibreglass as they have trapped air
- Convection
- Convection occurs in fluids
- (liquids and gases)
- When fluids are heated they expand and become less dense.
- This causes them to rise, to where it is cooler
- It then falls again, forming a convection current
- This causes them to rise, to where it is cooler
- Convection occurs in fluids
- Evaporation and Condensation
- Evaporation is a liquid turning into a gas
- It is caused by the most energetic liquid molecule escaping the liquid's surface
- The average kinetic energy of the remaining is less
- This causes it to cool
- The average kinetic energy of the remaining is less
- The rate of evaporation can be increased by
- Increasing the surface area
- Increasing the temperature
- Creating a draught across the surface
- It is caused by the most energetic liquid molecule escaping the liquid's surface
- Condensation is a gas turning into a liquid
- This often takes place on cold surfaces
- The rate of condensation is increased by
- Increasing surface area
- Reducing the surface temperature
- The particles lose kinetic/heat energy so move slower
- The lack of resistance means the particles are pulled back together
- Evaporation is a liquid turning into a gas
- Infrared Radiation
- Energy Transfer by Heating P1 - Unit 1.7 - 1.9
- Energy Transfer by Design
- Examiners love asking questions on the vacuum flask
- This will have glass walls with silver surfaces to reduce radiation
- A vacuum pocket so that air cannot circulate so there is no convection and poor conduction.
- A plastic cap to prevent evaporation.
- The greater the temperature difference between an object and its surrounding the greater the rate energy is transferred.
- The rate at which energy is depends on:
- Materials object in contact with
- Objects shape
- Objects surface area
- We maximise energy transfer to keep things cool
- Good conductors
- Painted dull black
- Increased air flow around the object
- We minimise energy transfer to keep things warm
- We minimise conduction, convection and radiaiton
- Good insulators
- White and shiny
- Prevent convection currents by trapping air in small pockets or vacuums
- Examiners love asking questions on the vacuum flask
- Specific Heat Capapcity
- Definition
- The amount of energy required to raise the temperature of 1 kilogram of a substance by 1 degree celsius
- Equation
- E = m x c x delta
- E = Energy transferred
- M = mass (kg)
- c = specific heat capacity (J/kg degrees Celsius)
- Delta = temperature change (degrees c)
- E = m x c x delta
- The greater the mass of the substance being heated the more energy needed to raise it by 1 degree.
- Definition
- Heating and Insulating Buildings
- The rate of energy transfer in and out of our house can be reduced with various methods
- Lost insulation prevents conduction
- Cavity wall insulation prevents convection
- Double glazing reduce conduction
- Draught proofing reduce convection
- Aluminium foil behind radiators reflects infrared radiation
- The U-value of an object tells us how much energy per second passes through it.
- This allows us to compare different materials
- The lower the U-value the better the insulator
- Solar Heating Panels contain water that is heated by the sun
- This can provide domestic hot water or used to heat buildings
- The rate of energy transfer in and out of our house can be reduced with various methods
- Energy Transfer by Design
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