Physics 1

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  • Created by: jxsskeene
  • Created on: 22-05-14 09:51
What three ways is heat transferred?
conduction, convection and radiation
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What's the saying about heat transferring?
The bigger the temperature difference between a body and its surroundings, the faster energy is transferred by heating.
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How do objects use infrared radiation?
All objects are continually emitting and absorbing infrared radiation from the surface of the object.
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What is are the two key points about infrared radiation?
An object that's hotter than its surroundings emits more radiation than it absorbs(as it cools down). An object that's cooler than its surroundings absorbs more radiation than it emits(as it warms up)
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What surfaces absorb and emit more radiation?
black, matt surfaces
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What surfaces reflect more radiation?
silver, shiny surfaces
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How does solar hot water panels work?
They contain water pipes under a black surface which absorbs the sun's radiation to heat the water in the pipes.
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What is the structure of a solid?
strong forces of attraction holding the particles in a fixed, regular arrangement. The particles don't have much energy so they only vibrate about their fixed positions.
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What is the structure of a liquid?
weak forces of attraction between the particles that are close together but can move past each other and form irregular arrangements, more energy than solid particles- move in random directions at low speeds.
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What is the structure of a gas?
Almost no forces of attraction between the particles that have more energy than liquids and solids and are free to move in random directions at high speeds.
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What is conduction?
(main form of heat transfer in solids) conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles. This causes a rise in temperature in the solid.
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Where is conduction faster?
In denser solids because the particles are closer together and so will collide more often passing on energy quicker.
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What are good conductors?
metals because the electrons are free to move inside the metal passing on the energy quicker.
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What is a name for materials that conduct heat a lot slower?
insulators- materials that have larger spaces between their particles
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What is convection?
(in liquids and gases) Occurs when the energetic particles move from the hotter region to the cooler region taking their heat energy with them
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What happens in convection?
The heated particles gain more energy, expand, become less dense so they rise, the heavier cooler particles are pushed down where they are heated. The cycle continues.
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What uses convection?
Immersion heaters, heat from radiator, kettles...
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What is condensation?
When a gas cools the particles slow down and lose kinetic energy, the attractive forces between the particles pull them together and then the gas becomes a liquid.
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What is evaporation?
Particles near the surface of the liquid can escape if the particles are travelling in the right direction and fast enough to overcome the attractive forces.
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What happens when a particle evaporates from a liquid?
The fastest particles are most likely to evaporate decreasing the average speed and kinetic energy of the remaining particles meaning the temperature of the remaining liquid falls- this is what happens when you sweat.
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What affects the rate of evaporation(4 points)?
temperature is higher(average particle energy will be higher), density is lower(forces between particles weaker), surface area is larger(more at the surface of the liquid to escape), airflow over the liquid is greater.
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What affects the rate of condensation(4 points)?
temperature is lower(average particle energy is lower), temperature of the surface the gas touches is lower, density is higher(forces between the particles will be stronger), airflow is less.
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What affects the rate of heat energy transfer?
the bigger the surface area the more infrared waves that can be emitted or absorbed by the surface, the object with a smaller the volume of two objects with the same surface area would have a faster heat energy transfer(more of the object is in
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carry on above q.
contact with the surroundings).
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What are the features of the vacuum flask(4)?
1.the glass bottle is double walled with a vacuum in between to stop conduction and convection. 2.The walls either side of the vacuum are silvered to prevent radiation. 3.the bottle is supported by an insulating foam to minimise heat conduction from
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carry on above q.
outside the bottle. 4.the stopper is made of plastic and filled with cork or foam to reduce conduction.
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How do people and animals in the cold control heat transfer?
the hairs on your skin stand up to trap a thicker layer of insulating air around the body limiting heat loss through convection(animals have fur)
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How do people and animals in the warm control heat transfer?
Your body diverts more blood to the surface of your skin so more heat can be lost through radiation
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How do you work out payback time?
initial cost/annual saving
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What is cavity wall insulation?
foam squirted into the gaps between the bricks stopping convection currents in the gap and radiation across the gap. The insulating foam and air pockets trap in it also helps reduce heat loss by conduction.
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What is loft insulation?
a thick layer of fibreglass wool laid out across the whole loft floor reduces conduction and radiation into the roof space from the ceiling.
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What is draught proofing?
strips of foam and plastic around doors and windows stop draught of cold air coming in and reduce heat loss by convection
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What does a hot water tank jacket do?
fibreglass wall reduces conduction and radiation
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What do thick curtains do?
reduce heat loss by conduction and radiation
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What is the u-value of a substance?
.
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What is specific heat capacity?
the amount of energy needed to raise the temperature of 1kg of a substance by 1degree celsius
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How do you work out the specific heat capacity?
energy(j)=mass(kg)*specific heat capacity(j/kgdegrees celcius)*temperature change(degrees celcius)
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What have high heat capacities?
heaters
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What are the 9 types of energy?
electrical, light, sound, kinetic, nuclear, thermal, (gravitational potential, elastic potential, chemical- these three are stored energy)
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What is the conservation of energy principle?
energy can be transferred usefully from one form to another, stored or dissipated but it can never be created or destroyed.
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What does it mean if an object is efficient?
The less energy that is wasted the more efficient the device is said to be
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How do you work out efficiency?
useful energy/power out divided by useful energy/power in
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What is the fact about device's and efficiency?
no device is 100% efficient and the wasted energy is usually spread out as heat
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What does dissipate mean?
spreading out into the surroundings
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How can waste energy be useful?
heat exchangers pump a cool fluid through the escaping heat rising the temperature of the fluid as it gains energy, the heat energy in the fluid can be converted to a useful form of energy.
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How do you work out energy?
energy=power * time
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how do you work out the no. of units(kwh)?
power(kw)*time9h)
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How do you work out the cost of a unit?
no. of units * price per unit
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What are the non renewable resources?
coal, oil, natural gas, nuclear fuels
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what are renewable resources?
wind, waves, solar, tides, hydroelectric, biofuels, geothermal, food
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What happens in power stations?
the fossil fuel is burned to heat water that turns to steam, the steam turns a turbine that turns a generator that creates electrical energy
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What are the energy processes at power stations?
chemical energy-heat energy-kinetic energy-electrical energy
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What is a nuclear power station?
Instead of fossil fuels nuclear fission of uranium or plutonium releases heat energy that heats water etc...
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How do wind turbines work?
Windmills on the coast have generators inside that are spun by the wind generating electrical energy.
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What are the pro's of wind turbines?
No pollution, no fuel costs, minimal running costs, no permanent damage to landscape
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What are the con's of wind turbines?
the wind is unreliable, expensive to set up, spoil the views, noisy
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How do solar cells work?
solar cells generate electric currents directly from the sunlight (used on a small scale-individual homes)
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What are the pro's of solar cells?
no pollution, energy is free, running costs very minimal
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What are the con's of solar cells?
sun isn't reliable and at night there is little energy, initial costs are high, expensive and not practical to connect to the national grid,
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How does hydroelectric power work?
requires the flooding of a valley by building a big dam, rainwater is caught and allowed out of the dam and allowed out through turbines.
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What are the pro's of hydroelectric power?
No pollution, provides an immediate response to a big increase in electricity, no fuel costs, minimal running costs, generates electricity on a small scale in small areas
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What are the con's of hydroelectric power?
Big impact on the environment due to the flooding of valley by rotting vegetation releasing methane and co2 and loss of habitat, unsightly, drought
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What is pumped storage?
most large power stations have huge boilers which have to be kept running all night even though demand is very low so there is a surplus of electricity at night this energy is stored in pumped storage. The spare energy is used to pump water up a
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carry on above question.
higher reservoir which can be released quickly in times of high demand such as at tea time, the water turns a turbine that turns a generator converting kinetic energy into electrical energy.
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How does wave power work?
Lots of small wave-powered turbines located around the coast and as waves come up in to the shore they provide an up and down motion which can be used to drive a generator
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What are the pro's of wave power?
No pollution, no fuel costs and minimal running costs, useful on small islands.
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What are the con's of wave power?
Initial costs are high, spoil view, hazard for boats, unreliable(waves die when wind drops)
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How do tidal barrages work?
Big dams built across river estuaries with turbines in them as the tide comes in it fills up the estuary and this water can be allowed through the turbine at a controlled speed, the source of the energy is the gravity of the sun and the moon.
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What are the pro's of tidal barrages?
No pollution, pretty reliable, no fuel costs and minimal running costs, has potential to generate a significant amount of energy.
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What are the con's of tidal barrages?
preventing free access by boats, spoils view, altering the habitat of wildlife, depending on the height of the tide the amount of energy created varies, don't work when the height is the same either side of the barrage, high initial costs
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How does geothermal energy work?
Only possible in volcanic area's where hot rocks lie near to the surface, the source of much of the heat is slow decay of various radioactive elements, steam and hot water rise to the surface and are used to drive a generator
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What are the pro's of geothermal energy?
free energy
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What are the con's of geothermal energy?
aren't many suitable area's, cost of building is very high, dangerous
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What are biofuels?
Used to generate electrical energy in the same way as fossil fuels, examples are straw, nutshells, woodchips, ethanol
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What is the point about biofuels?
Carbon neutral meaning the carbon dioxide absorbed as the plant or animal was alive is given off as it is burnt.
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How do non-renewable resources affect the environment?
all three fossil fuels release co2 when burnt which adds to the greenhouse effect and contributes to global warming, coal and oil release sulfur dioxide which causes acid rain, nuclear power is clean but nuclear waste is dangerous
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What is carbon capture?
Carbon capture storage is used to reduce the amount of co2 building up in the atmosphere by collecting the co2 from power stations before it is released whcih can be pumped into gas and oil fields where is can be stored safely.
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How is sulfur dioxide reduced in the atmosphere?
Taking the sulfur out before the fuel is burned
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What are the 6 things that need to be looked at when setting up a power station?
1. set-up cost, 2.set-up/decommissioning time 3.reliability issues 4.running/fuel costs 5.environmental issues 6.location issues
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How is electricity distributed?
via the national grid which takes energy from power stations to where its needed in homes and industry around the UK
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How does the national grid work?
To transmit the huge mount of power you need either as high current or high voltage but a high current looses loads of energy through heat and its cheaper to boost the voltage high and keep the voltage low.
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What is needed in the national grid?
Step up transformers bring the voltage up and step down bring it down round homes.
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What is the height of the wave from rest to crest?
amplitude(how loud)
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What is wavelength?
Full cycle from crest to crest
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What is the frequency?
(higher the frequency the higher the pitch) number of complete waves passing through a certain point per second measured in Hertz (Hz)
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What is the definition of transverse waves?
the vibrations are perpendicular to the direction of energy transfer of the wave.
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What are transverse waves?
Electromagnetic waves, waves on string, ripples on water, slinky spring wiggled up and down
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What is the definition of longitudinal waves?
the vibrations are parallel to the direction of energy transfer of the wave
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What are longitudinal waves?
sound waves, shock waves,slinky spring pushed at the end
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How do you measure wave speed?
frequency*wave length
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What can all waves be?
reflected, refracted, diffracted
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Reflection point 1?
Light travelling in the same direction reflects from an uneven surface(paper) at different angles.
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Reflection point 2?
Light travelling in the same direction from an even surface(mirror) is reflected at the same angle(clear reflection)
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What is the law of reflection?
angle of incidence=angle of reflection
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ray diagram
.
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What is diffraction?
All waves spread out when they pass through a gap, the amount of diffraction depends on the size of the gap relative to the wavelength e.g the narrower the gap and the longer the wavelength the more the wave spreads out.
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Diffraction images.
.
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What is refraction?
When a wave crosses a boundary between two substances it changes direction
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how to remember refraction?
TAGAGA- towards air glass away glass air
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refraction image.
.
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What are the electromagnetic waves?
radio waves, micro waves, infra red, visible light, ultra violet, x rays, gamma rays
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wavelength of em waves?
big at radio waves and gets shorter towards gamma rays.
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What are radio waves used for?
They can diffract around the curved the curved surface of the earth making it possible for radio signals,
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What are the seven colours?
red, orange, yellow, green, blue, indigo, violet
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What are microwaves used for?
communication to and from satellites because they pass easily through the earth's watery atmosphere, mobile phones
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What are infra red waves used for?
wireless remote controllers, optical fibres
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What is visible light used for?
photography
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What does sound do?
travel as waves caused by vibrating objects they are mechanical waves travelling faster in solids than liquids and gases and they can't travel in space(vacuum)
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What can sound waves do?
reflect by hard flat surfaces(echoes are reflected sound waves prevented by objects to absorb the sound and carpet and curtains) and they refract
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How is frequency and pitch related?
the higher the frequency the higher the pitch, lower the frequency the lower the pitch
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how is amplitude and loudness related?
the bigger the amplitude the louder the sound
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What is the absorption spectrum?
White light is made up of the colours of the visible spectrum and each colour has a different wavelength. When this light is passed through a gas certain wavelength's are absorbed and the patterns produced are called the absorption spectrum.
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What is red shift?
If the light source is moving away from us we would find the absorption spectrum lines are shifted towards the red end of the spectrum (longer wave length) and the faster the light source is moving the further the pattern is shifted. this is red shif
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How does red shift relate to the universe?
Light from the edge of the universe shows this pattern so we assume the edges of the universe are moving away from a single point called the big bang theory.
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What is the doppler effect?
The frequency of a source moving towards you will seem higher and wavelength will seem shorter. The frequency of a source moving away from you will seem lower and its wavelength will seem longer.
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What is the big bang theory?
All the matter and energy was compressed into a very small space and exploded from a single point and started expanding
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what is the steady state theory?
the universe has always existed as it is now and always will do
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What else proves big band theory?
there are uniform microwave radiation coming from all parts of the universe
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