Edexcel IGCSE Physics Thermal Energy Notes PDF

# EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 4-2 # Thermal Energy Edexcel IGCSE Physics pages 133 to 141 June 17th 2012 All content applies for Triple & Double Science ## Edexcel Specification Section 4: Energy resources and energy transfer b) **Energy transfer** describe how energy transfer may take p...

# EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 4-2 # Thermal Energy Edexcel IGCSE Physics pages 133 to 141 June 17th 2012 All content applies for Triple & Double Science ## Edexcel Specification Section 4: Energy resources and energy transfer b) **Energy transfer** describe how energy transfer may take place by conduction, convection and radiation explain the role of convection in everyday phenomena explain how insulation is used to reduce energy transfers from buildings and the human body. ## Thermal energy Thermal or heat energy is the energy that flows from a hot region to a cold region by one or more of the processes of: CONDUCTION CONVECTION and RADIATION The image shows a red cube titled "Hot Object" surrounded by "Cool Surroundings" Arrows indicate the direction of convection and radiation of Heat leaving the Hot Object. ## Thermal Conduction Thermal conduction is how thermal energy flows through a substance without the substance itself moving. Solids and metals are the best conductors, gases are the worst. A vacuum does not allow conduction. A poor conductor is called an insulator. The image shows a diagram with Heat Flow from LEFT to RIGHT The left side is labeled HOT and shows vigorous molecule movment The right side is labeled COLD and shows little molecule movment ## Conduction through metals Metals have an additional method of conduction. They have electrons that can move from one atom to another. These electrons can pass energy through the metal very quickly. The image shows a diagram with Heat carried in metals by the free electrons from LEFT to RIGHT The left side is labeled HOT and shows vigorous electron movment The right side is labeled COLD and shows less electron movment Most of the best conductors are metals. However, diamond, a non-metal, is an excellent conductor because it has very strong intermolecular bonds. ## Keeping warm with clothing Air is a good insulator. Clothes keep us warm by trapping air around our bodies. The more air layers are trapped the greater is the insulating effect of the clothing. Animals keep warm in a similar way by using fur or feathers to trap insulating layers of air around their bodies. The image shows an example of a man wearing a long sleeve sweater and vest and the text explains this article if clothing helps keep users warm. ## Rate of thermal transfer Heat transfer by conduction can increased by: - using a better conducting substance - decreasing the thickness of the substance - increasing the area of the substance - increasing the temperature difference across the substance ## Finding the best conductor - All the rods have the same length and cross-sectional area. - They are all heated equally at one end with the bunsen burner. - When the other end of a rod reaches a certain temperature the paraffin wax melts and the match stick falls off. - A match stick will fall off the best conductor first. - This should be the rod made of copper. Image shows a diagram to find the best conductor of material, including copper rod, iron rod, aluminium rod, brass rod, matchstick, paraffin wax. ## Comparing brass & wood - The gummed paper singes and burns first on the wooden side of the rod. - This is because the brass removes the heat away from the paper more quickly than the wood. - Brass is therefore the better conductor. Image shows a diagram showing the different rates of burning between wood vs brass materials. ## Water - a poor conductor - A boiling tube of water is heated near the top of the water. - Water boils at the top. - The bottom of the tube remains cool enough to hold. - This shows that water (and glass) only conduct heat relatively slowly. Image shows a diagram of test tube being heated at top with flame to show that the water will boil from the top. ## Air – a good insulator Image shows a collage of photos showing that air keeps things warm. There is an image of a bird with puffy feather, followed by people insulating a building with batting, followed by an image of a sick man in bed covered with blankets, and lastly an image of a person insulated in warm clothes in the cold. ## Question I Choose appropriate words to fill the gaps below: - Conduction is the main form of **heat** transfer in solids. This is because the molecules are relatively **close** together. - Extra heat energy makes the molecules **move** more. They pass on their extra vibrational energy to neighbouringles good. - Metals are **electrons** conductors of heat energy because they containtmany free which can move through the solid and **collide** energy. - The electrons give up their energy when they **collide** with other molecules. ## Question 2 Complete the table below: | substance | Conductor ir insulator| use | |-----------|------------------------|------------------------| | copper | conductor | cooking pan bases | | feathers | insulator | keeping birds warm | | water | conductor | cooling hot substances | | fibre glass | insulator | roof insulation | | steel | conductor | radiators | | air | insulator | clothing | ## Question 3 Explain why - newspaper wrapping keeps hot things hot, e.g. fish and chips, and cold things cold, e.g. ice cream, - fur coats would keep their owners warmer if they were worn inside out, - a string vest keeps a person warm even though it is a collection of holes bounded by string, - a concrete floor feels colder than a carpeted one even though they are at the same temperature. ## Convection Convection is the transfer of heat through fluids (liquids and gases) by the upward movement of warmer, less dense regions of fluid. Convection does not occur in solids. A vacuum does not allow convection. ## Convection currents - When molecules are heated they move more quickly and occupy more space. - Hotter fluids are therefore less dense than colder fluids. - Hotter fluids rise up to float on top of colder fluids. - A convection current is the path taken by rising hot fluids and sinking cold fluids. Image shows a diagram of convection current in a room with a person standing in the center. ## Convection in water - Potassium permanganate crystals are used to dye water purple. - When the bottom of the flask of water is heated warm less dense water rises. - The potassium permanganate dye rises with the warmed water. - When the water cools it becomes denser and sinks down to the bottom of the flask. Image shows a diagram of flask with potassium permanganate crystals being heated with a flame in order to illustrate how dye gets circulated in fluid due to heat. ## Heating a room by convection The image shows a diagram illustrating how a room is heated through convection. Starting from the radiator the hot air tends to rise towards the ceiling before cooling down by the Cold Window Lastly the cold air drop toward the floor towards the radiator, and hence the Convection cycle continues. ## Simple house water heating system - The boiler heats the water. - Hot water rises to the top of the boiler and up to the top of the storage tank. - Colder water in the tank falls to the bottom of the boiler to be heater. - A hot water tap draws water from the top of the storage tank. - The cold water supply replenishes the hot water drawn off. Image shows a diagram of a water based radiator system. Included is the expansion pipe, hot tap, storage tank, and boiler. ## Engine water cooling system - Water heated by the engine rises to the top of the engine. - This water is pumped into the top of the radiator. - The fan cools the water in the radiator. - Cooled water falls from the radiator into the engine. Image shows a diagram of an engine cooling system, using a fan to cool the water coming from the engine. ## Thermals - Heated air provides lift for a hot air balloon. - Heated land causes rising air currents called thermals. - Thermals can be used by gliders to provide lift. - Many birds also use thermals for lift. The image shows a collection of photos showing a Hot air balloon and a hang glider, which both uses thermals for lift. ## Sea and land breezes - During a hot day heated air rises up from land that is warmer than the sea. - A sea breeze consists of cooler air that moves in from the sea to replace the heated air. - At night the sea is often warmer than the land. - Air now flows to the sea. This is called a land breeze. The image shows two diagrams showing "Sea and land breezes". In day: The hot air rises. In night: The land cooler, land breeze form. ## Simple mine ventilation The fire causes hot air to rise up the shaft above it. Cooler, fresher air is drawn down the other shaft. Image show diagram illustration of concept mine ventilation shaft where fire pushes out the old air and fresh air comes down. ## Question I Choose appropriate words to fill in the gaps below: Convection is a method of heat transfer that only occurs **fluids** (liquids and **gases**). When part of a fluid is heated the **molecules** in that region move **quickly** and take up more space. The heated fluid expands and **becomes** less **dense** than the surrounding cooler fluid. The **rises** heated fluid. The upward path of the heated fluid is called a **convection** current. ## Question 2 Explain why - a hot drink will cool more slowly if a lid is put on the top of the drink, - clouds are often formed at the top of thermals, - top loading freezers are more efficient than those with side doors, - hot water radiators are best placed under a window. ## Thermal Radiation Thermal radiation is the transfer of energy by infra-red (IR) waves. Radiation is the only type of heat transfer that can travel through a vacuum through which it travels at the speed of light (300 000 km/s or 186 000 miles per second). Gases tend to allow radiation through better than liquids, liquids better than solids. ## Detecting thermal radiation Image shows a thermal image of two adults and one child, showing hotter areas in the colors red and yellow. - We can feel thermal radiation with our skin. - Special cameras can be used to take infra-red pictures. ## Thermal radiation & temperature All objects above absolute zero (-273°C) give off thermal radiation. The hotter an object the more radiation it gives off. The image shows a series of diagrams which illustrates that hot objects tends to give more heat. ## Surface and emission - Dark surfaces emit radiation better than bright surfaces. - Rough surfaces emit radiation better than polished surfaces. Image shows a diagram of a shiny copper sheet being measured for heat radiating off to a hand. ## Absorption & Reflection - Dark surfaces absorb radiation best. - Bright surfaces reflect radiation best. - Rough surfaces absorb radiation best. - Polished surfaces reflect radiation best. Image is a diagram that shows which dark surfaces are able to absorb radiation. ## Silvered surfaces This image contains three photos that demonstrate the way that silvered surface may used. These photos show Silvered Kettle, a marathon runner wrapped in reflective blanket, and a Firefighter. ## Question I Choose appropriate words to fill in the gaps below: Thermal radiation, also known as **heat** radiation, is how **heattraumelsnbijc** waves. Radiation travels equally in all **directions** and most quickly through a _vacuum_ where its speed is **300 000** km/s. All objects above absolute zero (**-273** °C) give off thermal radiation. Hot, **dark** and rough surfaces emit radiation best. Bright and **smooth** surfaces reflect radiation best. ## Question 2 Heat from the Sun can only reach us by thermal radiation. In hot countries houses are often painted white. Car radiators are black. Solar cells are black. Image is a collection of building in spain that are uniformly painted white. ## Heat losses from a house The image shows an illustration of a house with heat dissipating. Heat is lost through the roof (25%), the walls (35%), the window (10%) and through other cracks (15%, 15%). ## How heat losses are reduced | location | heat saving device(s) |-----|-----| |doors| |windows| |roof| |floors| |walls| ## Heating a room using a water radiator Hot water heats the metal radiator by conduction. The outer metal surface heats air in contact by conduction and radiation. Hot air circulates a room by convection. Image show a diagram radiator which pushes heat outward. ## Reducing heat transfer ### using a vacuum flask CONDUCTION - reduced by the vacuum, stopper, glass, cork and air spaces. CONVECTION - reduced by the vacuum, stopper and the trapped air spaces. RADIATION - reduced by the silvered glass walls. Diagram showing how to reduce heat using a vacuum flask. ## Question I is the form of energy **temperature** from a hot place to a cold one because of the **heatdiference** between these two places. Heat moves by conduction, **convection** and radiation. **thermal** energy is an alternative name for heat energy. ## Question 2 Write down the ways in which a vacuum flask reduces heat transfer |part of flask|processes reduced (eg'conduction') |---|---| |Outer cap/cup|conduction & convection |plastic cap|convection & conduction |shiny mirror surfaces|radiation |vacuum|conduction & conduction |sponge|conduction |air|conduction |plastic case|conduction ## Question 3 Write down six different ways in which heat flow from a house can be reduce in the table below |device or part of a house|processes reduced |---|---| |draught excluders|convection |double glazing|conduction & convection |reflecting strips behind radiator|radiation |loft insulation|conduction & convection |carpets|conduction |cavity wall insulation|conduction & convection ## Online Simulations - Conduction of heat in solids - eChalk - Relative conductivities of metal rods - eChalk - Convection currents in a room & fridge - eChalk - Sequential Puzzle on Heat Conductor order-by KT-Microsoft WORD - Energy House Simulation. For instructions click here. Worksheet for Energy House Simulation (KT) - Gas molecule simulation of convection falstad - Thermal Camera Pictures - falstad Black Body Spectrum-PHET-How does the blackbody spectrum of the sun compare to visible light? - Learn about the blackbody spectrum of the sun, a light bulb, an oven, and the earth. Adjust the temperature to see the wavelength and intensity of the spectrum change. View the color of the peak of the spectral curve - The Greenhouse Effect - PhET- Just how do greenhouse gases change the climate? Select the level of atmospheric greenhouse gases during an ice age, in the year 1750, today, or some time in the future and see how the Earth's temperature changes. Add clouds or panes of glass. - BBC KS3 Bitesize Revision: - Temperature and heat - Transfer of thermal energy-includes applet showing convection currents in a room - BBC Bitesize Revision: - Introduction Page on AQA Heat Transfer & Efficiency - Heat transfer by conduction & convection-includes applet showing convection currents in a room - Heat transfer by raidation - Reducing heat loss Test bite on Heat transfer, Energy transfers & Efficiency ## Thermal Energy Notes questions from pages 133 to 141 - Define what is meant by (a) thermal conduction, (b) convection and (c) thermal radiation. - Describe how the process of convection is involved in (a) heating a room using a convector heater, (b) a lava lamp. - Explain in terms of the methods of heat transfer how clothing keeps us warm. - Copy the pie chart on page 139 and explain how the heat loss from a house can be reduced from each of the five sections. - Answer the questions on page 141. - Verify that you can do all of the items listed in the end of chapter checklist on page 141.