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Heating and cooling revision notes for science

Extracts from this document...

Introduction

Heat can be transferred from place to place by conduction, convection and radiation.   Dark matt surfaces are better at absorbing heat energy than light shiny surfaces, however light, shiny surfaces are good reflectors of infra-red radiation.  Heat energy can be lost from homes in many different ways and there are ways of reducing these heat losses.

Infra-red radiation:-

  • All objects emit and absorb thermal radiation (infra-red radiation). The hotter an object is, the more infra-red radiation it emits.
  • Infra-red radiation is a type of electromagnetic radiation, which involves waves rather than particles.
  • Unlike conduction and convection, radiation can pass through the vacuum of space. This is why we can still feel the heat of the Sun, even though its 150 million km away from the Earth.

Kinetic theory:-

The kinetic particle theory explains the properties of the different starts of matter.

  • The particles insolids, liquids and gases have different amounts of energy.
  • They are arranged differently and move in different ways.
...read more.

Middle

The particles cannot move from place to place

They cannot be compressed or squashed

The particles are close together and have nowhere to move into

Properties of Liquids

Why are they like this?

They flow and take the shape of their container

The particles can move around each other

They cannot be compressed or squashed

The particles are close together and have nowhere to move into

Properties of Gases

Why are they like this?

They flow and completely fill their container

The particles can move quickly in all directions

They can be compressed or squashed

The particles are far apart and have space to move into

Conduction:-

Heat energy can move through a substance by conduction.

  • Metals are good conductors of heat but non-metals and gases are usually poor conductors of heat.
  • Poor conductors of heat are called insulators.
  • Heat energy is conducted from the hot end of an object to the cold end.

Heat conduction in metals:-

  1. The electrons in piece of metal can leave their atoms and move about in the metal as free electrons.
  2. The parts of the metal atoms left behind are now charged metal ions.
...read more.

Conclusion

large surface area compared to their volume. They lose heat to their surroundings very quickly and must eat a lot of food to replace the energy lost.

Large animals like elephants have a different problem. They have a small surface area compared to their volume. They lose heat to their surroundings more slowly and may even have difficulty avoiding overheating.

Elephants have large ears with a large surface area compared to their volume. These allow heat to be transferred from the elephant to its surroundings, helping to keep the animal cool.

In general, similar animals have different ear sizes depending on the climate in which they live. The arctic fox has much smaller ears than the fennec fox, which lives in the desert. The arctic fox must conserve its heat energy in the cold climate, while the fennec fox must avoid overheating in the hot climate.

Engineering design:-

Engineers design heat transfer devices so that they gain or lose heat energy efficiently.

For example -

Car radiators are flat, with many small fins to provide a large surface area. Similarly, household radiators are thin and flat, and may have fins so that heat energy is transferred to the room quickly.

...read more.

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