transfer of heat energy and its effects Flashcards
what is temperature?
temperature is the measure of how hot an object is
si unit of temperature
K (Kelvin)
what effect does the transfer of energy have on objects /substances?
when a substance is heated, it gains heat and expands. when a substance is cooled , it releases heat and contracts.
what happens when two objects are in contact?
heat energy is transferred from the hotter object to the colder object. the temperature of the colder object increases, while the temperature of the hotter object decreases. the temperature change continues until both objects reach the same temperature
what happens when oceans get overheated?
climate change includes global warming, which results in oceans absorbing more heat energy. this causes the oceans to expand and sea levels to rise.the rise in the sea level causes coastlines to be washed away. thus, coastal erosion increases.
examples of expansion and contraction in solids + ways to manage them
e.g. 1: in hot weather, railway tracks gains heat and expands. the railway track could buckle if it is made in one continuous piece. this may cause trains to derail.
way to manage : expansion gaps between railway tracks provide space for expansion.
e.g. 2: in hot weather, a concrete bridge expands. in cool weather, the bridge contracts. this may damage the bridge.
ways to manage: expansion joints between concrete slabs provide space for expansion. rollers under bridges allow expansion and contraction to take place safely
(application of expansion and contraction irl) opening a jar [explain]
it can be difficult to unscrew the tight lid of a jar. placing the lid in hot water can make it easier to unscrew the lid. the metal lid expands more than the glass jar. this makes the lid less tight and hence easier to unscrew.
(application of expansion and contraction irl) bimetallic strips [explain]
a bimetallic strip is made up of two metals that expand at different rates upon the same change in temperature. brass, which expands and contracts more than steel, can be joined together with steel to make a bimetallic strip. bimetallic strips can be found in thermostats and bimetallic thermometers. thermostats are used to keep the temperature of an appliance constant.
bimetallic strip in an electric iron: turning the knob lowers or raises the contacts and sets the temperature of the electric iron, at which it switches off. the bimetallic strip in the iron is straight and the contacts touch each other. the circuit is complete and electricity flows through it. the bimetallic strip expand when heated. the brass strip expand more than the steel strip which causes the bimetallic strip to bend downwards. the circuit becomes open, switching off the iron. when the bimetallic strip cools down, it becomes straight and the contacts touch each other again.
bimetallic strip in food thermometer: food thermometers measure the temperature of food. in a food thermometer, the bimetallic strip is made into a coil. one end of the strip is attached to a pointer. as the temperature changes, the different expansion rates of the metals cause the coil to unwind (when temp increases) or tighten (when temp decreases). thus, the pointer moves over the scale.
(application of expansion and contraction irl) liquid-in-glass thermometer [explain]
a liquid-in-glass thermometer is a narrow glass tube sealed at both ends, with a bulb at one end. the bulb is partially filled with a liquid such as mercury or alcohol. when the temperature around the bulb increases, the liquid in the bulb heats up, expands and rises up the narrow glass tube. when the temperature decreases, the liquid in the bulb cools down, contracts and falls back into the bulb.
(application of expansion and contraction irl) hot air balloon [explain]
when air in a hot air balloon is heated, its volume increases. the mass of air remains constant as the number of air particles does not change. since the mass of air in the balloon does not change while its volume increases, the density of the air decreases. the hotter and less dense air rises, which causes the hot air balloon to float.
what is conduction? +example
conduction is the transfer of heat energy without the physical movement of the medium
a can feels colder than the carton when taken out from a refrigerator. the can is made of metal while the carton is made of paper. since metal is a better conductor of heat than paper, it conducts heat energy away from our hands more quickly. hence, the can feels colder than the carton.
conduction in solids vs in liquids and gases
solids are generally better conductors of heat than fluids. the particles in solids are arranged more closely to one another then the particles in liquids and gases. the close arrangement of particles in solids enables transfer of heat energy occur more quickly
what is convection?
convection is the transfer of heat energy from one place to another with the physical movement of a medium.
convection in liquids [example]
as the heated water expands, its volume increases. since the mass of the water remains constant. the increase in its volume results in a decrease in its density. the hotter and less dense water rises to the top of the beaker. the cooler and denser water in turn sinks to the bottom of the beaker. the hotter and less dense water rises and the cooler and denser water sinks continuously. convection currents are formed in the water. heat energy is transferred throughout the water. after some time, heat energy is evenly distributed in the water.
convection in gases [example]
the air above the candle heats up and expands. it becomes less dense and rises up chimney A. cooler air, which includes the smoke from the smouldering paper, moves down chimney B to take the place of the hotter air that has risen. the cooler air is heated by the candle, becomes less dense and rises up chimney A. this forms a cycle of convection currents.
what is radiation?
radiation is the transfer of heat from a hotter body to a cooler body without the need for a medium. e.g. the space between the sun and earth is a vacuum. heat energy is transferred from the sun to the earth by radiation. the only way heat energy can be transferred from a hotter object to a cooler object in a vacuum is by radiation.
heat energy that is transferred by radiation may be absorbed or reflected.
what is the greenhouse effect?
the greenhouse effect is the warming of the surface of the earth. this happens when heat is prevented from leaving earth’s atmosphere by radiation. greenhouse gases, such as carbon dioxide, trap heat within the atmosphere and keep earth warm to support life. greenhouse gases are produced when we burn fossil fuels such as coal, crude oil and natural gas. our heavy reliance on fossil fuels increases the amount of greenhouse gases in the atmosphere. as a result, there is an increased greenhouse effect, which increases the earth’s temperature. this is known as global warming.
what are some effects of global warming?
melting polar ice caps and shrinking glaciers. the melting of large volumes of ice can cause the sea level to rise. increased absorption of heat energy by the oceans can cause water bodies to expand, resulting in rising sea levels. rising sea levels can lead to floods along coastal areas.
what are some factors that affect the rate of conduction?
- different materials conduct heat at different rates. for example, metal conducts heat better than wood.
- water is a poor conductor of heat. a test tube is filled with water and ice at the bottom. the water at the top of the test tube is heated. the water near the top of the test tube boils, while the ice at the bottom of the test tube does not melt easily. this is because the water does not readily transfer heat energy from the top of the test tube to the bottom of the test tube.
what are factors that affect the rate of radiation?
- [the temperature of an object. the hotter the body of an object, the higher the rate of radiation from the object.]
- [surface area of the object. an object with a larger surface area has a higher rate of radiation. ] for example, electronic appliances such as computers contain a heat sink. the heat sink has a large surface area, which allow heat to be radiated from the appliance quickly
- type (texture and colour) of surface.
- absorption of radiation: two identical objects are painted black and white respectively. they are then filled with water of the same temperature and placed under the sun. after some time, the water in the black container has a higher temperature than the water in the white container. [this shows that black surfaces are better absorbers of radiation than white surfaces. rough and dull surfaces are also better absorbers or radiation than shiny, smooth surfaces.]
- emission of radiation: hot water at 100 degrees is poured into both white and black containers. after a while the water in the black container has a lower temperature than the water in the white container. [this shows that black surfaces are better emitters of radiation than white surfaces. dull, rough surfaces are also better emitters of radiation than shiny, smooth surfaces.]
how is conduction applied in a frying pan?
the metal base of the frying pan is a good conductor of heat. it allows heat energy to be transferred quickly from the heat source to the food. the wooden handle of the frying pan is a poor conductor of heat. our hands do not get burnt as heat energy is not easily conducted through the handle to our hands.
how is conduction applied in woollen clothing?
air is a poor conductor of heat and is thus a good insulator of heat. porous materials, such as wool, trap pockets of air, making them excellent heat insulators. clothes that are made from wool keep us warm as heat from out body is not readily conducted through the air that is trapped by the wool.
how is conduction applied in double-glazed windows?
double-glazed windows are used to reduce heat loss through the windows. a layer of air trapped between the glass panels forms an insulating layer.
how is convection applied in air conditioners?
air conditioners are usually placed near the top of the room. warm air, which is less dense, rises and collects under the ceiling. the air conditioner cools the warm air, which becomes denser and sinks to the bottom of the room.
