Please enable JavaScript.

Coggle requires JavaScript to display documents.

heat by isabelle - Coggle Diagram

- - - - by movement of particles in medium
    - - requires movement of particles in medium
        
        particles in fluids able move freely
        
        transfer heat from one region to another by convection
        
        particle in solid not able move freely
        
        only vibrate at fixed positions, vacuum no particle in it
    - - in circulatory manner called convection current
        
        convection current set up due to change in density of fluid
    - - volume of region increases but mass of particles remain constant
        
        hence density decreases
    - - hot fluid rises, cold fluid sinks, convection current set up
    - - sample of blue crystal placed in water at bottom of beaker
        
        bottom of beaker then gently heated
        
        circulation of blue stream of water moving upwards, downwards
        
        aka convection current
      - water is heated, expands, density decreases. hence rises up
        
        cooler part of water, which is denser, sink replace heated water
        
        it is in turn heated, rises
        
        this cycle repeated set up convection current
    - - box with two chimneys used
        
        candle placed under one of chimneys
        
        smouldering paper placed above other chimney
        
        smoke flows down chimney, move towards lit candle, rises up from chimney
      - air above lit candle heated, expands
        
        hence density decreases, rises out of chimney
        
        cooler surrounding air denser at other chimney (represented by smoke
        
        sinks through chimney replace hot air
    - - electric kettle
        
        heating element place at bottom of kettle
        
        when electricity turned on, heating element heats up water at bottom
        
        hot water rises, cold water sinks. thus, convection current set up in kettle
        
        water in kettle heated up more uniformly, efficiently
      - hot water system
        
        boiler installed at lower part of hot water system
        
        water is heated up in boiler
        
        hot water rises to upper part of storage tank
        
        cold water in water supply tank sinks
        
        into boiler to replace hot water
      - air conditioner
        
        placed at the top of wall
        
        cold air from air conditioner sinks into room
        
        hot air rises, cooled by air conditioner, sinks down
        
        cycle repeated to set up convection currents in room
        
        hence, room is cooled efficiently
    - - sea breeze
        
        during day, land heated up faster than sea
        
        result, air above land warmer than above sea, it rises up
        
        cooler, denser air from sea flows in, replace rising hot air
        
        movement of air from sea to land = sea breeze
      - land breeze
        
        during night, land loses heat much faster then sea
        
        result, air above sea warmer than above land, it rises up
        
        cooler, denser air from land flows towards sea
        
        replace rising hot air
        
        movement of air from land to sea = land breeze
  - - - mode does not require medium, so can happen in vacuum
    - - heat energy fro infrared radiation = radiant heat
    - - term
        
        absorber
        
        any objects that take in heat in form of radiation
        
        reflector
        
        any objects that bounce off radiation
        
        radiator / emitter
        
        any objects that give off heat in form of radiation
    - - when object absorbs radiant heat, its temperature increases
    - - surface temperature of object
        
        if surface of object has higher temperature, radiate heat at higher rate
      - colour and texture of object
        
        black, dull, rough surfaces are best absorbers & emitters of radiant heat
        
        poor reflectors of heat
        
        white, shiny, smooth surfaces are poor absorbers & emitters of heat
        
        good reflectors of heat
      - surface area of object
        
        if object has larger surface area, rate of heat transfer by radiation faster
    - - white clothes
        
        white colour > poor absorber of heat
        
        when person walks under sun, not feel overheated if put white clothing
      - hot water containers
        
        hot water containers shiny appearance
        
        reduce heat loss by radiation from inside of containers to surroundings
        
        this way, water stay warmer for longer period of time
      - refrigerator
        
        cooling coils of refrigerator painted black, ensure heat lost quickly
        
        black colour radiate heat faster to surroundings
  - - - vibration of particles
        
        all matter is made up of particles
        
        solids, closely packed together, vibrate at their fixed positions
        
        conduct heat better than liquids and gases
        
        particles in solid closely packed together than in liquids, gases
        
        hence, easier for particles, cause neighbouring particles to vibrate vigorously
        
        when heated, particles gain heat, vibrate more vigorously
        
        cause neighbouring particles to vibrate vigorously too
        
        slow process of heat transfer
      - motion of free electrons
        
        in metals, free electrons that can move about freely
        
        during heating, free electrons help
        
        transfer heat energy from heated region to cooler region quickly
        
        make metals much better heat conductors than non-metals
        
        different metals conduct heat at different speeds
        
        fast process of heat transfer
    - - e.g. metal
    - - e.g. non metals : glass, wood, plastics
    - - good conductors
        
        cooking utensils - conduct heat quickly to cook food
        
        radiators - conduct heat from hot water to surroundings quickly
        
        heating element in electric kettles - conduct heat quickly heat up water
      - poor conductors (insulators)
        
        handles - protected from scorching when holding them during cooking
        
        woollen jacket, trap air - prevent heat loss from body to cold surroundings
- - - - region of higher temperature called heat source
      - region of lower temperature called heat sink
    - - temperature of the object increases
      - the object changes in size or physical state
    - - not a form of energy
- - - - contraction
        
        size : decrease
      - expansion
        
        size : increase
      - how? particles in object gain more kinetic energy, push each other further apart through their vigorous motion
        
        hence volume occupied by particles in object increases
        
        while mass remains unchanged
    - - gases expand and contract faster than liquids and solids
      - e.g. brass, iron metals. brass expands + contracts faster than iron during heating/cooling
    - - expansion
        
        density : decrease
        
        reason
        
        vigorous motion push one another further apart, increase space occupy
        
        mass remains unchanged, ratio of mass/volume decreases, density decreases
        
        density = mass/volume
        
        particles in substance gain heat energy during heating, motion increases
        
        causes : mass remains the same, volume increases
        
        experiments
        
        liquids
        
        gases
        
        solids
        
        metal ball cannot pass metal ring
      - contraction
        
        density : increase
        
        causes : mass remains the same, volume decreases
        
        less vigorous motion make closer, decrease space occupy
        
        particles in substance lose heat energy during cooling, motion decreases
        
        mass remains unchanged, ratio mass/volume increase, density ^