Physics P1

Physics P1

1. Energy

   • Everything stores energy. The more more energy the things store, the more work they do, Energy has the unit Joules (J)
     • Energy is a not a physical substance. In a chemical reaction, the mass of chemicals before and after is the same, but the amount of energy stored in the chemicals change. Some energy may spread to the surroundings, or may be absorbed from the surroundings.

2. Infrared Radiation

   • All objects emit and abosrb infrared radiation. Shiny light coloured surfaces absorb infrared radiation slower than black matte surfaces. They reflect infrared radiation well. Hotter surfaces emit radiation faster than cooler surfaces.
     • Many things affect global warming. One theory is that the sea water is dark coloured and absorbs the infrared radiation from the sun faster than the ice does.

3. Kinetic Theory

   • Melting is when a solid changes to a liquid. When the solid is heated, the particles vibrate vigorously. Bonds between particles break and reform so that particles can change places.
     • Freezing is when a liquid cools and changes to a solid.
       • Boiling is when a liquid changes to a gas when the liquid is heated. The particles break their bonds and can move around randomly.
         • Condensing is when a gas cools and changes to a liquid.

4. Particles

   • In solids, particles vibrate and are held together by strong bonds.
     • In liquids, particles move around each other but cannot escape due to weak bonds.
       • In gases, particles move randomly and bonds are very weak.

5. Conduction and Convection

   • If one end of the solid is heated, particles vibrate more and shake their neighbours. Conduction transfers energy from one particle to another through the solid.
     • If one part of a liquid or gas is warmed, the particles vibrate and take up more space. The warm region of the gas or liquid expands, becoming less dense and rising above the cooler, denser region. This is called convection.
       • Convection currents spread heat through liquids and gases that are heated from the base or cooled from the top.

6. Evaporation and Condensation

   • Evaporation is when a liquid changes to a gas at temperatures lower than boiling point.
     • Evaporation is quickest if it is warm (more particles have enough energy to break bonds linking them.
       • Water Evaporates from the earths surface and cools forming clouds. Water Vapour condenses into liquid rain. This is the water cycle.

7. Rate of energy transfer

   • When hot objects cool, energy is transferred to the surface by conduction and from the surface by convection. Hotter objects lose energy more quikly than cooler objects.
     • The ratio of surface area o volume affects the rate of eat loss. If the surface area is larger, energy is transferred quicker form the object

8. Payback time (insulating buildings)

   • Payback time is the time taken to save as much money as it costs to install an energy saving measure.
     • Payback time = installation cost / annual saving

9. Specific Heat Capacity

   • Energy is transferred to an object that heats up, or from an object that cools down.
     • Energy transferred to or from a material = mass x specific heat capacity x temperature

10. Energy transfer and waste

    • The law of conservation of energy says energy cannot be created or destroyed when it is transferred. All energy is usefully transferred, dissipated or stored. The energy that spreads to the surroundings is called waste energy.
      • A Sankey diagram shows energy transfer in a device. The energy input is shown on the left side of the arrow. The arrow splits. Each section shows the energy output form. The width of each arrow shows the proportion of energy is represents.
      • Efficiency
        • Efficient devices do not waste as much energy. (Efficiency = useful energy out / total energy in). The answer is always a decimal lower than 1. Convert decimals to a percentage by multiplying by a 100

11. Alternatives to electricity

    • Electrical appliances transfer the energy supplied by electricity into something useful.
      • Mains electricity is convenient, safe and pollution free at the point of use. However, generating electricity in power stations causes pollution.

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