conduction convection evaporation

• what are the four ways in which thermal energy can be transferred

  convection, conduction, radiation, evaporation
• explain conduction


  the heat source will cause the particles nearest to it to gain kinetic energy. these particles will vibrate more and collide with their neighbours, causing their neighbours to vibrate, the process continues until all particles are vibrating more, creating thermal equillibrium with the heat source.
• what make the best conductors

  metals make the best free conductors because there are free electrons with kinetic energy. conduction is very unlikely in gas and liquid.
• explain convection


  method of heat transfer for liquids and gases, as the particles are able to move and flow past eachother. heated partiles vibrate more vigorously and move around, spreading apart and causing the liwuid to expand. the fluid is now less dense and is able to rise upwards.
• explain convection currents


  after the process of convection, the heated particles displace the colder particles at the top of the container. cooler particles have less energy and they vibrate less so the particles get closer together making the fluid more dense and therefore sinking. the denser fluid then gets heated and the process repeats.
• explain evaporation


  when a substance evaporates, only the particles at the top turn into vapour. it may be achieved at any temp if another source of energy is present (when particles boil, all the particles are boiling not just the ones at the top, happening at boiling point.) . it causes cooling and then the particles with most kinetic energy escape the surface, therefore the kinetic energy of the particles that remain (total internal energy) increases.
• definition of absorb


  take in or soak up (energy or a liquid or other substance) by chemical or physical action.
• definition of boiling


  near or at boiling point. the action of bringing a liquid to the temperature at which it bubbles and turns to vapour.
• change of state


  the process of the change from one state (solid, liquid, gas) to another (solid, liquid, gas).
• condensing


  The change of state from a gas to a liquid
• conduction definition


  the process by which heat or electricity is directly transmitted through the material of a substance when there is a difference of temperature
• Conductor definition


  A material that allows heat and electricity to pass through it.
• Convection definition


  the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
• Emit definition


  produce and discharge (something, especially gas or radiation).
• Free electron definition


  electron within a conducting substance (as a metal) but not permanently attached to any atom.
• Heating food in a saucepan over a gas flame is inefficient. Suggest why.

  some of the energy is wasted on the surrounding and some energy is used to heat the pan so not all the energy i being used on the food.
• A new saucepan has been designed that heats up food much faster than a traditional saucepan. The diagram below shows the two saucepans. one has a black matte surface + fins and one has a shiny silver surface.Describe how the features of the new saucepan cause the food to heat up faster than when the food is heated in the traditional saucepan.

  the fins create more surface area of the pan in contact with the food therefore the heat energy is transferred to the food quicker. the black matte surfaces absorbs infrared radiation more efficiently than a shiny surface does.therefore heat is absorbed by the pan quicker than a shiny pan.
• State the relationship between the temperature of the saucepan and the rate at which the saucepan emits infrared radiation.

  the higher the temperature, the most infrared radiation is emitted.
• A new design for a kettle has also been suggested. It is made from two layers of plastic separated by a vacuum. After the water in the kettle has boiled, the water stays hot for at least 2 hours.

  Here is a diagram of the design.

  vacuum,water, two layers of plastic.


  no particles in a vacuum so it was reducing possibility for conduction and convection to occur from the water to the air.