Gases do not conduct heat
A vacuum cannot conduct heat
The best conductors are non-metals
Conduction currents occur only in liquids
- The kinetic energy is the energy of any matter in motion. The small particles that make up matter are constantly moving. They have kinetic energy. The kinetic energy of particles in matter is called thermal energy. When thermal energy is transferred, it is known as heat. The word thermal means ‘heat’.
- Heat is the thermal energy that flows from an object. Heat flows from an object at higher temperature to an object at lower temperature.
- The transfer of heat through matter without the actual movement of particles from their position is called conduction. Conduction occurs in solids, liquids and gases, but solids usually conduct heat better than liquids or gases.
- In solids, the particles are held very close to each other. They vibrate constantly. When we heat one part of a solid, the particles gain heat energy and start vibrating faster. During their vibration they bump into nearby particles and also cause them to vibrate fast. In this way, the particles of hot part of a solid transfer heat to those in the colder parts.
- Different materials conduct heat at different rates. Materials which allow heat to flow through them easily are called good conductors of heat. Solids such as metals are good conductors of heat. Materials which do not allow heat to flow through them easily are called bad conductors of heat or heat insulators. Solids such as wood, glass, plastic, styrofoam, etc. are bad conductors of heat. All liquids (except mercury which is a liquid metal) and gases are also bad conductors of heat.
- The process of conduction in liquids and gases is very slow as compared to solids (metals). The particles in liquids and gases are not held closely together. The particles have less chances to bump into other particles in liquids and even lesser in gases. That is why, the transfer of heat energy from fast-moving particles to neighbouring particles is slow. Water and air are bad conductors of heat.
- Although most non-metals are poor conductors, Graphite (an allotrpoe of carbon) is the only non-metal which is a good conductor of electricity.
- Radiation is the transfer of heat energy from a region of high temperature to a region of low temperature by infrared radiation. Unlike conduction and convection, radiation takes place without the need of any particles. Because no particles are involved, radiation can work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth.
- In a vacuum, heat transfer primarily occurs through radiation, as there is no medium for conduction or convection.
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