Physics 1a

Physics 1a

1. Radiation

   • IR Raditation
     • Absorbed and emitted by every object.
       • Affected by its temperature gradient.
         • If an object is warmer than its surroundings, it will emit more IR radiation and absorb less.
         • If an object is cooler than its surroundings, it will absorb more IR radiation and emit less.
     • A large surface area to volume ratio
       • More IR radiation is emitted
   • The amount of IR radiation absorbed and emitted depends on the surfaces's colour and texture.
     • Matt, black surfaces are the best absorber and emitter of IR radiation.
     • Shiny, silver surfaces are the worst absorber and emitter of IR radiation.
       • Shiny silver surfaces can reflect IR radiation.

2. Conduction

   • Mainly in Solids
     • Vibrating particles collide into each other and pass on their extra kinetic energy.
     • Quicker in denser solids
   • Metals are good conductors
     • Free Electrons which can move easily.
       • A faster and more efficient way of passing on the energy.
     • Even better in short, wide rods
   • Direction of heat transfer = Hot to Cold
     • Temperature Increase

3. Convection

   • Mainly in Fluids (Liquids and Gases)
     • Involves particles with a lot of kinetic energy.
       • Particles move from the hotter to cooler area.
         • The energy is carried along.
           • To form a Convection Current
             • Density Change
               • Particles that are less dense, rise.
                 • Less dense particles displace the denser ones.
                   • More dense Particles, sink.
               • Constant circulation of heat
   • An example is a radiator in a room.

4. Kinetic Theory

   • Heating a substance, provides it with more kinetic energy, allowing it to change state.
     • Solids
       • Strong bonds between particles, holding them together.
       • Particles vibrate in the fixed, regular shape
       • Contain little amounts of kinetic energy
     • Liquids
       • Weak bonds between particles, keeping them close together.
       • Contain quite a lot of kinetic energy
       • Particles can slide past each other in random directions to form an irregular shape.
       • Evaporation
         • Particles must be in the right direction and have high amounts of kinetic energy
           • If they are then they can escape from a liquid at temperatures below the boiling point
             • The amount of kinetic energy within the particles reduces
               • As a result the overall temperature in the liquid reduces too, as the particles with the most kinetic energy are removed.
             • Factors which speed up this process:
               • The surface area being larger
                 • More space to evaporate off
                   • Greater Airflow
                     • Evaporating particles are taken away
               • Liquids with high temperatures
                 • Particles have more kinetic energy
               • Liquids with lower densities
                 • Weaker bonds between particles so they are easier to break
     • Gases
       • No bonds in between particles
       • Contain high amounts of Kinetic Energy
       • Particles are free to move in random directions.
       • Condensation
         • As a gas cools it loses its Kinetic Energy
           • The bonds strengthen and bring the particles closer together
             • A liquid forms when the gas particles bond closer together
               • Factors which speed up this process:
                 • A contacting surface with a lower temperature
                 • A gas with a lower temperature
                   • Less Kinetic Energy
                 • A gas with a higher density
                   • Stronger bonds
                 • Lower Airflow
                   • Particles are less likely to be taken away before they hit the surface.

5. Energy Efficiency

   • Pay Back Time = Cost of Investment / Saving Per Year
   • Cost Effectiveness = Saving Per Year / Cost of Insulation
   • Different Types of Insulation
     • Cavity Wall Insulation involves foam being pumped into a wall
       • Prevents heat loss by convection and radiation
     • Loft Insulation involves fibreglass wool being laid across the floor
       • Prevents heat loss by conduction and radiation
     • Draught Excluders are strips of foam and plastic that are stuck on doors and windows
       • Prevents heat loss by convection
     • Hot Water Tank Jackets are pieces of fibreglass wool that cover the tank
       • Prevents heat loss by conduction and radiation
     • Thick Curtains
       • Prevent heat loss by conduction and radiation
     • U-Values show how good a material is at being an insulator
       • The lower the U-Value, the better the insulator
         • The slower the rate of heat transfer

6. Conservation of Energy

   • Energy can be transferred or transformed but it cannot be created or destroyed.
     • Different forms of Energy
       • Electrical, Light, Sound, Kinetic, Nuclear, Thermal, Gravitational Potential, Elastic and Chemical
         • Forms of Potential Energy (Stores of Energy): Chemical, GPE, Kinetic, Elastic
         • Energy is only useful when it is changed into a different form
           • Efficiency = Useful Energy Output / Total Energy Input
             • In all devices some of the output energy is wasted energy
               • This wasted energy is normally thermal energy
                 • Sankey Diagrams are a visual display of this
             • Comparing Different Appliances
               • The amount of energy transferred depends on its power and the time the appliance is on.
                 • Energy = Power x Time
                 • Units of Measurements: Energy = Joules (J) / Kilowatt-Hours (kWh) Power = Watts (W) / Kilowatts (KW)
                   • Cost of Electricity
                     • Units (kWh) = KW X Hours
                       • Cost = Units (kWh) x Price

7. Specific Heat Capacity

   • energy stored (J) = mass (kg) x specific heat capacity (J/kg°C) x temperature change °C
     • Calculating a substance's Specific Heat Capacity
       • specific heat capacity (J/kg°C) = energy stored (J) / mass (kg) x temperature change °C
   • The amount of energy needed to raise 1kg of a substance by 1°C
     • Water has a Specific Heat Capacity of 4200 J/kg°C
   • The amount of energy a substance can store