Physics P1 - Energy (1)

Physics P1 - Energy (1)

1. Infrared radiation

   • All objects absorb and emit infrared radiation
   • Shiny light coloured surfaces absorb infrared radiation slower than black matt surfaces, and reflect the radiation well
   • Hotter surfaces emit radiation faster than cooler surfaces. Also, objects warm up if they absorb more radiation than they emit.

2. Kinetic theory

   • The bonds between particles are strongest in solids and weakest in gasses
   • In SOLIDS: Particles vibrate and are held together by strong bonds
   • When a solid is heated, the particles vibrate more vigorously and so the bonds between the particles break and reform, so the particles can change place
   • In LIQUIDS: Particles move around each other but cannot escape due to weak bonds
   • In GASSES: Particles move randomly due to very weak bonds
   • Particles do not change as they change state, they just behave differently

3. The amount of energy stored is measured is Joules

4. Energy is transferred - it cannot appear or disappear

5. Evaporation, condensation, and pressure

   • Evaporation is when a liquid changes to gas at temperatures lower than boiling point
   • Evaporation is quickest when when it is either warm (as more particles have enough energy to break the bonds linking them) or if the liquid has a large surface area, or if it is windy (so the vapour above the liquid's surface does not become saturated)
   • The water cycle
     • Water evaporates from the Earth's surface and cools, forming clouds. Water vapour condenses into liquid rain, and when it rains the water is once again on the Earth's surface, and so the cycle repeats.
   • At high altitudes, wind speeds are high and air pressure is low, so it is easier for particles to evaporate
   • Evaporation occurs at the surface at low temperatures, but boiling occurs throughout the liquid at boiling point

6. Conduction, convection, and rate of energy transfer

   • If one end of a 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 more, taking up more space. The warm region expands, becoming less dense and rising above cooler denser regions. This is CONVECTION
   • Convection currents spread heat through liquids or gasses that are heated from the base or cooled from the top.
   • EXTRA: Metals are good conductors because the electrons are free to move rapidly from hotter to cooler regions, transferring energy
   • When hot objects cool, energy is transferred TO the surface by conduction and FROM the surface by convection. Hotter objects lose energy more quickly than hotter objects.
   • The surface area to volume ratio affects the rate of heat loss. If the surface area is larger, energy is transferred quicker from the object.

7. We detect energy in different ways, but it cannot exist in different forms