The flashcards below were created by user
ghoran
on FreezingBlue Flashcards.
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why are copper or aluminium pans better than iron ones
beacuse copper and aluminium are better conductors of heat than iron
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why do duvets feel warmer than blankets
because duvest contain trapped air which is a good insulator , whereas in ablanket there is little or no trapped air
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what design features of outdoor clothes helps you keep warm
- clothes that are black on the outside and silver on the inside (with the silver facing you)
- tight cuffs
- trapped air in the material of the clothes
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why is the element at the bottom in an electric kettle
because hot water rises due to convection currents , so the whole of the water in the kettle will benifit from the element , whereas if the element was at the top only the surface of the water in the kettle would get heated
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why is the cooling element at the top of the refrigerator
because cool a2ir sinks due to convection currents also the warmer air will be at the top of the refrigerator , so the cooling element will cool the warm air which will then sink
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if pieces of black paper and white paper are laid pn snow insunchine , what is likely to happen
- the snow under the black paper will melt because black surfaces are good absorbers of radiation
- the snow under the white paper will stay the same because white surfaces are good reflectors of radiation
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why are cups from a take-away food oulet made of polystrene and not thin plastic
because polystrene contains trapped air which is a good insulator so it will reuce heat loss by conduction , however although plastic is an insulator it isnt as effective as polystrene
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many people use a sleeping bag when they sleep in a tent . sleeping bags designed to keep a person warme have a fibre filling
a) complete the following sentence : the fibre is designed to reduce heat transfer by ..... and ....
b) explain why the fibre is good at reducing heat loss from a person in the sleeping bag
- a) the fibre is designed to reduce heat trasnfer by conduction and convection
- b) the sleeping bag is sealed so most of the air is trapped and little air can escape , air is a good isnulator , also there is trapped air actually inside the material of the sleeping bag
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calculate the payback time and answer the questions
e) which method of insulation would you install first
f) which is most effective
g) which is the most cost effective
- a) 2 years
- b) 4 years
- c) 22.5 years
- d) 1/15 years
- e) foam filled cavity because most of the heat is lost through the walls and it gives you the biggest annual saving per year and the payback time is relatively short and it is relatively cheap to install
- f) foam filled cavity , double glazing
- g) draught proofing
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the double glazed window consists of two 6mm panes of glass , 10mm apart in a sealed plastic frame . the space between the glass panes is a vacuum . the double-glazed window cuts heat down heat loss because : glass is a .... conductor and the panes are ..... times thick as a single pane . plastic is a .... insulator and so it ....very little heat . there is no ..... or ...... through the vaccum because a vacuum is an empty space with no particles
- poor
- 1.5
- good
- conducts
- conduction
- convection
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the U value measures :
how well a building componenet , e.g. a wall , roof or a window , keeps heat inside a building .For those living in a warm climate the U-value is also relevant as i is an indicator of how long the inside of a building can be kept cold
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the higher the U value the :
more heat flows through so a good U-value is a low one as ypu want to keep heat inside the building or outside the depending on the climate you live in
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U-values measure how effective a material is as an ..........
insulator
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the ..... the U-value , the better the material is as an insulator
lower
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different substances at the same temperature store different amounts of heat (thermal energy) for the same mass of material . this is called
specific heat capacity
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materials which need to gain lots of energy to warm up also :
release loads of enrgy when they cool down again , they can store a lot of heat
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the specific heat capacity of a substance is the :
amount of heat energy required to raise the temperature of 1kg of the substance by 1°C
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water has a specifc heat capacity of
4200 J/kg°C
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the formula for specific heat capacity is as followed
heat transfered = mass*specific heat capacity*temperature change
what are the units
- heat transfered is measured in joules (J)
- mass is measured in kilograms (kg) note make sure that the mass in your equation is in kilograms , if it isnt convert it
- specific heat capacity is measured in joules per kilogram per degress celsius (J/kg/°C)
- temperature cahnge is meausred in degress celsius (°C)
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substances which have a very high specific heat capacity such as ...... , and ..... can be used in ... .... ... examples are : car radiators , oil filled radiators and electric storage heater containg concrete
- water
- oil
- concrete
- heat strorage devices
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generally , liquids have a .... specific heat capacity than solids . This means that liquids need .... .... ....than solids for the same rise in temperature
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the materials used in heaters usually have a ....... specific heat capacity so they can .... ....... .... of heat energy
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water has a reallly high specific heat capacity , it is also a ..... so it can easily be ..... ... in .... - ideal for .... .... systems in buildings
- liquid
- pumped around
- pipes
- central heating
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electric storage heaters are designed to :
store heat energy at night (when the when electricity is cheaper and then release it during the day . they store heat using concrete or bricks which have a high specific heat capacity
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