CHapter 10

• Conduction is the transfer of heat energy without physical movement of the medium
• Context: The object is hotter than the environment and you want it to cool down faster. Material should be used: Metal 'Metal' is a good conductor of heat. This increases the rate of thermal energy transfer loss by conduction
• Context: The object is hotter than the environment and you want it to cool down slower. The material should be used: Plastic/Air Plastic/Air is a poor conductor of heat. This decreases the rate of thermal energy transfer loss by conduction
• Context: The object is colder than the environment and you want it to heat up slower. The material should be used: Plastic/Air Plastic/Air is a poor conductor of heat. This decreases the rate of thermal energy transfer gain by conduction
• Context: The object is colder than the environment and you want it to heat up faster. The material should be used: Metals Metal is a good conductor of heat. This increase the rate of thermal energy transfer gain by conduction
• Radiation is the transfer of heat energy from a hotter body to a cooler body without the need for a medium
• Context: The object is hotter than the environment and you want it to cool down slower. Surface properties used: Silver, shiny, and smooth surface. The silver, shiny, and smooth surface is a poor emitter of radiation. This decreases the rate of thermal energy transfer lost by radiation
• Context: The object is colder than the environment and you want it to heat up faster. Surface properties used: black and dull surface. Black and dull surfaces are good absorbers of radiation. This increases the rate of thermal energy transfer gained by radiation.
• Context: The object is colder than the environment and you want it to heat up slower. Surface properties used: Shiny, silver, and smooth surface. Shiny, silver, and smooth surfaces are poor absorbers of radiation. This decreases the thermal energy transfer gain by radiation
• Convection is the transfer of heat energy from one place to another by the physical movement of the medium.
• Context: Heating up a room or container. Arrangement: The heating source should be at the bottom. The air/water around the heat source is heated, expands, becomes less dense, and rises. The cooler air/water at the top being denser, sinks. This process repeats and the convection current is set up
• Context: Cooling down a room or container. Arrangement: cold source at the top. The air/water around the cold source is cooled, contracts, becomes denser and sinks. Warmer air/water at the bottom, being less dense, rises. The process repeats and a convection current is set up
• The fins of the heat increase the surface area. Hence thermal energy lost by radiation and conduction is increased.
• Temperature is a measure of how hot an object is. The SI unit is (K).
• Heat always transfers from a region of higher temperature to a region of lower temperature
• When an object of higher temperature is in contact with an object of lower temperature, the heat energy will flow from the object of higher temperature to the object of lower temperature until both object acquire the same temperature
• Useful application of heat energy: Cooking food, which kills germs and makes our food safe to eat. Keeping us warm through a campfire by burning wood at a campsite Drying wet laundry when we place it under the sun.
• Harmful effect of heat energy: Heat injuries when we exercise in the sun for a long time. - Damage to electronic and electrical components due to overheating. - Damage to physical structures such as railway tracks due to expansion.
• After heating, the metal ball gains heat and expands. The particles of the metal ball continue to vibrate randomly about their fixed position, but more vigorously than before. The particles move further apart to cause the volume of the ball to increase. The increase in the volume of the metal ball causes it not to pass through the ring
• The mass of an object does not changed after expanding or contracting
• By the density formula, the density of the metal ball will also decrease as the same amount of particles are packed into a larger volume.
• A thermostat maintain the temperature of appliances within a desired range
• Electric Oven and iron are appliances that use thermostats which contain a bimetallic strip that uses expansion and contraction of solid for the thermostat to function.
• When the temperature of the appliance is within the desired range. The bimetallic strip is straight. The electrical contacts touch and the circuit is closed. The cooling unit of the fridge is switched on
• A bimetallic strip is made of two strips of metal that expands at different rates upon the same changes in temperature. It can be used to control the temperature of appliances
• As the temperature within the fridge decreases, both the bimetallic strip will contract. However, the metal at the top contracts more than the metal at the bottom when both lose the same amount of heat energy. Hence the bimetallic strip bends upwards when the temperature of the fridge is too cold. The electrical contacts no longer touch and the circuit is opened. The cooling unit of the fridge is switched off to prevent it from cooling further.
• Making the bimetallic strip bend upwards can be done by placing the metal which expands by a larger amount below a metal which expands by a smaller amount, for the same amount of heat gain
• A substance that expands more for the same amount of heat gain will also contract more when cooled for the same amount of heat loss.
• Making the bimetallic strip bend downwards can be done by placing the metal which expands by a larger amount above a metal which expands by a smaller amount for the same amount of heat gain or loss
• Negative effect by expansion: Buckling of railway tracks occurs either there is insufficient or no gap between the consecutive pieces of metal used to lay the tracks. - To solve this, a sufficient gap between the consecutive pieces of metal is needed to allow for expansion
• What is likely to happen if both ends of the metal bridge are fixed? Why is the bridge placed on rollers? What function does the expansion gap serve?

  If both ends of the bridge are fixed, expansion of the bridge on hot days would cause the bridge to buckle and deform, damaging the bridge in the process. Hence one end of the bridge rests on rollers so that the bridge can expand and move freely into the expansion gap provided to prevent damage from expansion
• Cables are given extra length and allowed to sag from vertical poles. This extra length aims to solve the contraction of the overhead cable which causes it to become shorter and increases the likelihood of it snapping, on cold days. By providing extra length, the cables will still contract to become shorter but less likely to snap.
• Conduction is the process of transferring heat between neighboring particles in a medium without a net movement of the particles
• Heat transfer by conduction can occur in liquid, solid and gas but not in a vacuum
• Heat transfer by conduction occurs when more energetic particles of the medium collide into less energetic, neighboring particles to transfer them energy
• Since solids, liquid and gases are made of particles, it is possible to conduct heat in them
• A vacuum does not have particles for colliding. Hence, conduction is not possible in a vacuum and can stop heat transfer by conduction totally as conduction needs particles of medium to take place but there aren't any particles in a vacuum.
• Conduction is most effective in solids which means heat transfer by conduction is fastest in solids as the particles of the solid are very closely packed. Therefore, the transfer of energy by colliding or knocking into neighboring particles from more energetic to less energetic particles is fastest and most efficient in solids