physics

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  • Created by: rkarokohe
  • Created on: 22-05-17 12:24
what type of radiations transmits heat energy ?
heat energy is transmitted by infra-red radiation
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complete this sentence
hotter objects emit more infrared radiation than cooler objects
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what type of surface are good absorb and good emitters of infrared radiation
dark,matt surfaces are good absorb and good emitters of infrared radioation
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What type of surfaces are poor absorbs and poor emitters of infrared radiation?
Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation
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What type of surfaces are good reflectors of infrared radiation?
Light, shiny surfaces are good reflectors of infrared radiation.
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What can we say about the arrangement of particles (and kinetic energy) in solids?
In solids, the particles are close together and arranged in a regular pattern. The particles are not moving from place to place but they are vibrating. Particles have a small amount of kinetic energy
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What can we say about the arrangement of particles (and kinetic energy) in liquids?
In liquids, the particles are close together and not arranged in any pattern. The particles are moving from place to place. Particles have a large amount of kinetic energy.
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What can we say about the arrangement of particles (and kinetic energy) in gases?
In gases, the particles are far apart. The particles are moving very rapidly from place to place. Particles have a very large amount of kinetic energy.
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Describe how heat energy can be transferred by conduction.
Conduction takes place best in solids because the particles are close together. If we heat the solid, the particles gain kinetic energy and vibrate more. This vibration is passed onto nearby particles causing them to vibrate, spreading the heat energ
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Why are metals very good conductors of heat?
Metals are very good conductors of heat because they have free electrons which can move and transfer the heat energy.
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Describe how heat energy can be transferred by convection
Convection takes place in liquids and gases. When they are heated, the particles move further apart. This causes the liquid/gas to become less dense and move up. Cooler regions sink to take their place. This is a convection current.
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How is heat lost by evaporation and gained by condensation?
When a liquid turns to a gas (evaporation) the particles gain kinetic energy. This energy is transferred from the surface, which cools down. When a gas turns to a liquid (condensation) the particles lose kinetic energy. This energy is transferred to
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Describe the factors that increase the rate of evaporation
These conditions make evaporation faster: • Warmer conditions • Dry conditions (not humid) • Windy conditions
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Explain why animals in hot conditions usually have large ears and animals in cold conditions usually have small ears
Heat is lost faster from objects with a large surface area. Animals in hot conditions have to lose body heat so they often have larger ears which increases their surface area helping to lose heat. Animals in cold conditions have to retain their body
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What is meant by an insulator? Describe in terms of particles how these work.
Insulators reduce heat transfer. They have large gaps between particles so vibrations cannot easily pass between the
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What does the U-value tell us about an insulator?
The U-value tells us the amount of heat energy that can pass through an insulator. Good insulators have a low U-value.
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What is meant by the specific heat capacity of a substance?
The specific heat (also called specific heat capacity) is the amount of heat required to change a unit mass (or unit quantity, such as mole) of a substance by one degree in temperature.
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Complete this sentence: Energy can neither be ……….. nor ………….. but it can be transferred.
The specific heat capacity of a substance tells us the amount of energy required to change the temperature of 1kg of the substance by 1oC
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When energy is transferred, some is often wasted. What happens to wasted energy?
Energy can neither be created nor destroyed but it can be transferred.
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How do we calculate the efficiency of a device?
Efficiency = useful energy out x 100 total energy in The unit of efficiency is %. Remember that efficiency cannot be greater than 100%
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State the energy transfers taking place in a food mixer. Which energy transfers are wasted?
Wasted energy is eventually transferred to heat, warming the surroundings. This energy is spread out and is less useful.
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How do we calculate the total amount of energy transferred by an appliance in a given time
E = P x t E = energy in Joules (or kilowatt-hours) P = power in Watts (or kilowatts) t = time in seconds (or hours)
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How many kilowatt-hours are used by a heater with a power of 2kW running for 2 hours.
Electrical energy is transferred to kinetic energy, heat energy (wasted) and sound energy (wasted)
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What is meant by the payback time for different methods of home insulation?
Different methods of home insulation save different amounts of money in reducing energy use. The payback time tells us how long it takes to save enough money to pay for the cost of installation.
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How do we calculate the payback time?
Payback time = cost of installation saving per year
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Loft insulation costs £200 to install and saves £100 each year. Calculate the payback time.
Payback time = 2 years.
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Complete: In some power stations, water is heated and turned to ……….. This drives a ……….. connected to a ……………….. generating electricity
In some power stations, water is heated and turned to steam. This drives a turbine connected to a generator generating electricity.
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What is meant by geothermal energy?
Geothermal energy is available in volcanic areas. Hot water and steam rise to the surface. The steam is used to drive turbines, generating electricity.
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When can small-scale electrical production be useful (eg solar cells).
Small-scale electrical production can be useful when it is not economical to connect to the National Grid, for example roadside signs.
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What is meant by carboncapture and storage?
Carbon dioxide (eg from power stations) is trapped and stored so it does not enter the atmosphere. This can be done in old oil and gas fields e.g. under the North Sea.
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State the advantages and disadvantages of generating electricity by burning fossil fuels.
Advantages • Very reliable, generating lots of electricity when we need it. • Relatively cheap Disadvantages • Non-renewable. Fossil fuels are running out. • Produces carbon dioxide which leads to global warming.
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State three examples of fossil fuels?
Fossil fuels include: • Coal • Oil • Gas
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Which elements are used to generate electricity in nuclear power stations?
Nuclear power stations use uranium or plutonium.
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State the advantages and disadvantages of generating electricity by nuclear power.
Advantages • Very reliable, generating lots of electricity when we need it. • Does not produce carbon dioxide and does not contribute to global warming. Disadvantages • Expensive to build and decommission • Potentially dangerous. If an accident occur
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State the advantages and disadvantages of generating electricity by solar power.
Advantages • Does not produce carbon dioxide and does not contribute to global warming. • Renewable. Will not run out. Disadvantages • Unreliable. Will not generate electricity on very cloudy days or at night.
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State the advantages and disadvantages of generating electricity by wind power
Advantages • Does not produce carbon dioxide and does not contribute to global warming. • Renewable. Will not run out. Disadvantages • Unreliable. Will not generate electricity on days when there is little wind. • Wind turbines contribute to visual p
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What is meant by the startup time for a power station? Which fossil fuel power stations have the shortest startup time?
The startup time is the time taken to produce electricity when a power station is switched on. Gas-fired power stations have the shortest startup time, followed by oil. Coal has the longest startup time.
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Why are nuclear power stations so expensive?
Nuclear power stations are very expensive to build and decommission (dismantle at the end of their useful life).
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State the advantages and disadvantages of generating electricity by hydroelectric power.
Advantages • Does not produce carbon dioxide and does not contribute to global warming. • Renewable. Will not run out. Disadvantages • Only useful in certain countries (those with lots of fast-flowing rivers). • Dams destroy habitats by flooding.
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State the advantages and disadvantages of generating electricity by wave and tidal power.
Advantages • Does not produce carbon dioxide and does not contribute to global warming. • Renewable. Will not run out. Disadvantages • Only useful in certain countries (for example the UK). • Tidal power destroys habitats e.g. birds.
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How can we match the supply of electricity to the demand for electricity?
Electricity demand changes during the day (for example very low at night). Power stations cannot easily be turned on and off and electricity cannot easily be stored. We need large power stations (eg nuclear) to provide the base-load and then gas-fire
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How does a pumped-storage system help us to manage the changing demand for electricity?
In pumped storage, when electricity demand is low (eg at night), electricity is used to pump water uphill into a reservoir. This stores energy as gravitational potential energy. When demand is higher, the water is allowed to flow downhill through tur
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How does a pumped-storage system help us to manage the changing demand for electricity?
Overhead power lines are cheaper to install and easier to maintain/repair. However, they can be affected by weather and can be a hazard e.g. to low-flying aircraft. They also cause visual pollution (pylons are unattractive). Underground power cables
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State the advantages and disadvantages of generating electricity by burning biofuels
Biofuels include wood-chippings from the timber industry and methane gas from landfills. These are renewable and relatively cheap. Although carbon dioxide is released, in some cases (eg wood), this was taken in by the growing plants.
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What is meant by the National Grid?
The National Grid is a system of transformers and power cables.
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What does a step-up transformer do in the National Grid?
A step-up transformer increases the voltage of the electricity supply from the power station before it is transmitted through power cables.
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What does a step-down transformer do in the National Grid?
A step-down transformer decreases the voltage of the electricity supply from the power cables before passing to peoples’ homes.
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Why is electricity transmitted at extremely high voltages through power cables from power stations?
Increasing the voltage means that we can transmit electricity at a lower current. A lower current reduces the energy lost as heat as the electricity passes through the cables
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Card 2

Front

complete this sentence

Back

hotter objects emit more infrared radiation than cooler objects

Card 3

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what type of surface are good absorb and good emitters of infrared radiation

Back

Preview of the front of card 3

Card 4

Front

What type of surfaces are poor absorbs and poor emitters of infrared radiation?

Back

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Card 5

Front

What type of surfaces are good reflectors of infrared radiation?

Back

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