Physics term 1 year 10

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    • How is heat transferred?Give 3 ways.
      • 1)Radiation, (infrared)
        • All objects continually emit (from the surface of the object) & absorb infrared radiation. The hotter an object is the more radiation it radiates in a given time.
          • An object that's hotter than its surroundings emits more radiation than it absorbs as it cools down. This is the opposite for An object that's hotter than its surroundings emits more radiation than an object that's cooler than its surroundings. We can feel infrared radiation if we stand next to something hot.
        • Which is the emission of electromagnetic waves as it doesn't need particles to transfer heat.
        • Dark, matt surfaces absorb the radiation falling on them much better than light, shiny surfaces like silver because silver reflects, that is why vacuum flasks have silver inner surfaces( to reflect the heat and trap it). Dark colours also emit much more than light.
      • 2)Conduction
        • These need particles to pass on heat which is why in vacuum flasks there is a vacuum to stop the transfer of conduction and convection.
        • It occurs mainly in solids and is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles. This process continues all the way through the solid which makes it increase in temperature. The surface also warms up.
        • Conduction is faster in denser solids as the particles are closer together & so will collide more often to pass energy on. Materials that have larger spaces between their particles conduct heat energy much more slowly these are known as insulators.
        • Metals are good conductors because of their free electrons. At the hot end the electrons move faster & collide with other free electrons transferring energy. As they move freely it's a faster way of transferring energy through the metal rather than slowly passing it between jostling neighbouring atoms. This is why heat energy travels faster in metals.
      • 3)Convection
        • These need particles to pass on heat which is why in vacuum flasks there is a vacuum to stop the transfer of conduction and convection.
        • Convection happens in fluids(liquids & gases). It occurs when the more energetic particles move from the hotter region to the cooler region & take their heat energy with them.
        • E.G water particles when heated at one end gets more energy and they move faster so there's more distance between the particles & the water expands becoming less dense. The reduction in density means that the hotter water will rise above the cooler water & displaces the colder water out of the way. So that it sinks towards the bottom where the source of heat is.
        • The process goes on in a circular way as due to the hot water cooling & becoming denser it drifts towards the bottom where it's pushed back to the source of heat. Convection current is what we call this.
    • What is kinetic theory & the 3 states of matter?
      • Liquid
        • Weaker force of attraction between particles & are still close together but can move past each other( as they have more energy). They form an irregular arrangement. Move in random directions at a slow speed.
      • Solid
        • Strong forces of attraction keep the particles close together, vibrating(as they don't have much energy) in a fixed/regular position.
      • Gas
        • Have almost no force of attraction and have more energy. They are free to move/travel in random directions at high speeds.
      • Kinetic theory- when you heat a substance you give its particles more kinetic energy. They vibrate/move faster. It causes solids to melt & liquids to boil.

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