P1- Physics- P1.1 - 1.9 (Energy Transfer by Heating)

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  • Created by: Em_New99
  • Created on: 15-05-15 16:05

Infrared Radiation

Key points

  • Infrared radiation is energy transfer by electromagnetic waves
  • All objects emit infrared radiation.
  • The hotter an object is, the more infrared radiation it emits in a given time.

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The Electromagnetic Spectrum

Radiowaves, microwaves, infrared radiation, visiable light, ultraviolet rays and X-rays are parts of the electromagnetic spectrum.

Electromagnetic waves are electric and magnetic waves that travel through space.

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Energy From the Sun

The sun emits all types of electromagnetic radiation. Fortunatly for us the earths atmosphere blocks most of the radiation that would harm us. But it doesnt block infrared radiation.

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Infrared Radiation (Continued)

The Greenhouse Effect

The atmospher acts like a greenhouse. 

  • Gases in the atmosphere such as water vapour, methane and carbon dioxide, trap infrared radiation from the earth. This makes the earth warmer than it would be if it had no atmosphere

The earth is becoming too warm

  • If the polar ice caps melt- it will cause sea levels to rise. Reducing our uses of fossil fuels would help reduce the production of 'greenhouse gases'
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Surfaces and Radiation

Key Points

  • Dark matt surfaces emit more infrared radiation than light shiny surfaces
  • Dark matt surfaces absorb more infrared radiation than light shiny surfaces
  • Light, shiny surfaces reflect more infrared radiation than dark matt surfaces
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States of Matter

Key Points

  • Flow, shape, volume and density are the properties used to describe each state of matter
  • The particles in a solid are held next to each other in fixed positions
  • The particles in a liquid move about at random and are in contact with each other 
  • The particles in a gas move about randomly and are much further apart than particles in a sold or liquid

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Solid- Does not flow, Fixed shape, Fixed volume and higher density than a gas

Liquid- Does flow, Fixed volume, No Fixed volume and higher density than a gas

Gas- Does flow, No Fixed volume, No Fixed gas and low density compared with a solid or liquid

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Conduction

Key Points

  • Metals are the best conductors of energy
  • Only happens in solids
  • Materials such as wool and fibreglass are the best insulators
  • Conduction of energy in a metal is due to mainly free electrons transferring energy inside the metal
  • Non-metals are poor conductors because they do not contain free electrons

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Materials like wool and fibreglass are good insulators as they contain air trapped between the fibres. Trapped air is a good insulator. We use materials like fibreglass for loft insulation and for lagging water pipes.

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Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles

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Convection

Key Points

  • Convection is the circulation of a fluid (liquid or gas) caused by heating
  • Convection takes place only in liquids and gases
  • Heating a liquid or a gas makes it less dense so it rises and causes circulation
  • Covection occurs when the more energetic particles move from a hotter reigion to a cooler reigon and take their heat energy with them.
  • Convection currents are all about changes in density

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Why do fluids rise when heated?

Most fluids expand when heated. This is because the particles move about more, taking up more space. Therefore the density decreases because the same mass of fluid now occupies a bigger volume. So the heated part of the fluid makes that part less dense and therefore it rises.

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Exam Tip

When you explain convection, remember it is the hot fluid that rises, NOT 'heat'.

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Evaporation and Condensation

Key Points

  • Evaporation is when a liquid turns into a gas
  • Condensation is when a gas turns into a liquid
  • Cooling by evaporation of a liquid is due to the faster-moving molecules escaping from the liquid

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Factors that affect the rate of evaporation

  • Increasing the surface area of the liquid
  • Increasing the temprature of the liquid
  • Creating a draught of air across the liquid's surface

Factors that affect the rate of condensation

  • Increasing the surface area
  • Reducing the surface temperature
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Energy Transfer By Design

The Vacuum Flask

  • The Vacuum- An area with no particles which prevents conduction, convection and radiation
  • Silvered inside to prevent radiation
  • Stopper (Lid) prevents evaporation and convection
  • The Vacuum between the two walls of the container cuts out energy transfer by conduction and convection between the walls
  • Glass is a poor conductor so there is little energy transfer by condction through the glass
  • The spring supporting the double walled container is made of plastic which is a good insulator 

(http://qph.is.quoracdn.net/main-qimg-124344241b64fbfd283a28615b62e67b?convert_to_webp=true)

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Specific Heat Capacity

Key Points

  • The greater the mass of an object, the more slowly its temprature increases when its heated.
  • The rate of temprature change of a substance depends on: The energy supplied to it; its mass; its specific heat capacity.
  • Storage heaters use off-peak electricity to store energy in special bricks
  • Specific Heat Capcity tells you how much energy something can store

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The specific heat capacity of a substance is the energy needed or energy transferred to 1kg of the substance to raise its temprature by 1°C.

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The unit of specific heat capacity is the joule per kilogram per °C

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For a known change of temprature of a know mass of a substance

E= m x c x  θ

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Specific Heat Capacity (Continued)

E= m x c x θ

  • E is the energy transferred in Joules, J
  • M is the mass in kilograms, Kg
  • C is the specific heat capacity, J/Kg°C
  • θ is the temprature change in degrees celsius, °C

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To find the specific heat capacity you need to the above equation:

C= E / m x θ

Here are some of the SHC of some substances:

  • Water- 4200J/Kg°C
  • Oil- 2100J/Kg°C
  • Aluminium- 900J/Kg°C
  • Iron- 390J/Kg°C
  • Copper- 490J/Kg°C
  • Lead- 130J/Kg°C
  • Concrete- 850J/Kg°C
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Heating and Insulating Buildings

Key Points

  • Energy from our homes can be reudced by fitting- Loft insulation; Cavity wall insulation; Double glaszing windows; draught proofing; Aluminium foil behind radiators.
  • U-values tell us how much energy per second passes through different materials.
  • Solar heating panels do not use fuel to heat water but they are expensve to buy and install

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Ways of reducing energy transfer at home

Loft Insulation- Uses things such as fibreglass to reduce energy transfer through the roof. Fibreglass is a good insulator as the air between the fibres helps reduce conduction

Cavity Wall Insulation- Reduces energy loss through the outer walls of the house. The 'cavity' of an outer wall makes up the space between the two layers of brick that make up the wall. The insulation is pumped into the cavity. It traps air in small pockets reducing convection currents.

Aluminium Foil- Behind a radiator, reflecting the heat back into the room

Double-glazed windows- have two glass panes with dry air or a vacuum between the panes. Dry air reduces energy transfer by conduction. A vacuum cuts out convection too 

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Heating and Insulating Buildings (Continued)

U Values

The lower the U-value, the more effective the material is as an insulator.

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Payback Time

The time taken for something to produce savings to match how much it costs

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Energy Transfer

Nine Types of Energy

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  • Electrical energy- Whenever a current flows
  • Light energy- From the Sun, light bulbs, ect
  • Sound energy- From loudspeakers or anything nosy
  • Kinetic energy- From anything that moves
  • Nuclear energy-  released from nuclear reactions
  • Thermal energy- Flows from hot objects to colder ones
  • Gravitational potential- Possesed by anything which can fall
  • Elastic potential- Stretched springs, elastic, rubber bandss
  • Chemical energy- Possesed by food, batteries and fuels
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