P1 - Energy Transfer By Heating Flashcards
How does temp. effect the amount of infrared radiation an object emits?
The hotter the object, the more infrared radiation it emits.
What type of object emits infrared radiation?
All objects emit infrared radiation.
What are radio, micro and infrared radiation waves?
They are electromagnetic waves.
Give three more examples of electromagnetic waves.
Visible light, X-Rays, ultraviolet rays
How fast to electromagnetic waves travel?
300,000,000 metres per second (ms^-1)
What blocks UV rays from the Sun?
The Earth’s ozone layer.
What electromagnetic wave doesn’t Earth’s atmosphere block?
Infrared Radiation
Explain the Greenhouse Effect
- Short wavelength IR passes through the glass and warms the objects within.
- Longer wavelengths are emitted by the objects trapping the IR inside the greenhouse.
Name three gases that trap IR.
Water vapour, carbon dioxide and methane.
Give one effect of the planet warming
Polar ice caps will melt causing the sea level to rise.
Define infrared radiation
Energy transfer by electromagnetic waves
How does a PIR sensor work?
They work by detecting infrared radiation.
What is the best reflector of IR?
Light, shiny, smooth surfaces
What surface is best at absorbing and emitting IR?
Dark, Matt surfaces
Give the four main properties of a solid.
- It doesn’t flow.
- It has a fixed shape.
- It has a fixed volume.
- It has a high density.
Give the four main properties of a liquid.
- It flows.
- It fits the container shape.
- It has a fixed volume.
- It is more dense than gas.
Give the four main properties of a gas.
- It flows.
- It fits the container.
- Its volume can be changed.
- It has a low density.
Give the process of a liquid to a gas.
Vaporisation
Give the process of a liquid to a solid.
Solidification/Freezing
Give the process of a gas to a solid.
Condensation
Give the process of gas to liquid.
Condensation
Give the process of solid to gas.
Sublimation
Give the process of solid to liquid.
Melting
Give an example of sublimation.
Solid carbon dioxide i.e dry ice
How are the atoms in a solid arranged?
They are in uniform fixed positions and vibrate about their position.
How are the atoms in a liquid arranged?
The particles are in contact with each other but can move randomly.
How are the particles in gas arranged?
Particles move at random very fast and very far apart. The density is very low.
What state’s particles have the most kinetic energy?
Gas particles have the most kinetic energy then liquid particles.
What type of material is the best conductor of energy?
Metals are the best conductors.
What materials are the best insulators?
Wool and fibreglass are good insulators.
Why does metal conduct energy?
Metals have free electrons which diffuse and collide with other electrons and ions transferring kinetic energy.
How do electrons move in a metal?
They move randomly.
Why don’t non-metals conduct energy well?
Non-metals don’t contain free electrons to transfer kinetic energy.
How does energy transfer take place in non-metals?
The atoms vibrate and shake each other which is less effective than free electrons.
Why are wool and fibreglass good insulators?
Air gets trapped in the fibres and air is a good insulator.
What states does convection occur in?
Liquids and gases.
How does an old boiler use convection?
Hot water rises to the top of the tank which is connected to a hot water tap.
Define convection
The circulation of a fluid caused by heating it.
Why do hot fluids rise?
Heating a fluid makes it less dense causing it to rise above the more dense fluid and causes circulation in a sealed unit.
Why does the fluid become less dense?
The particles in the fluid gain kinetic energy and move more so it occupies a bigger volume
What are the advantages of using data logging software?
The risk of human error is reduced.
Why do matt surfaces absorb radiation?
A matt surface is rough meaning the IR is scattered and absorbed at multiple points.
Why don’t smooth surfaces emit much radiation?
They have a smaller surface area.
What is evaporation?
This is the change of state from liquid to gas.
How does cooling by evaporation work?
Faster moving molecules i.e with more kinetic energy, escape from the liquid reducing the temperature.
Give three ways of increasing the speed of evaporation.
- Increasing the surface area of the liquid.
- Increasing the liquid’s temperature.
- Creating a draught of air across the surface.
Explain what happens to the liquid molecules during evaporation.
- As the temp. increases the molecules gain more kinetic energy.
- The intermolecular forces weaken.
- Fast moving molecules escape into gas.
What factors affect the rate of condensation?
- Increasing the surface area.
- Reducing the surface temperature.
What properties does a car radiator have?
- Large surface area.
- Gaps to allow convection and radiation.
How does a flask keep a drink warm or cool?
- Contains a vacuum to stop conduction and convection.
- Has silver surfaces to stop radiation.
- Plastic shell and supports which are good insulators.
- Plastic cap stops cooling by evaporation.
Why does the liquid in a flask eventually cool?
The preventative measures do not entirely stop heat transfer.
How is a radiator used in a computer?
A metal heat sink sits on top of some components and has a large surface area. Some are also accompanied by a fan to improve ventilation.
How does the temp. difference between an object and it’s surroundings effect the rate of energy transfer?
The bigger the temp. difference the faster rate of energy transfer.
What design factors affect the energy transfer of an object?
- The materials the object is in contact with.
- The object’s shape.
- The object’s surface area.
How is a desert fox adapted to its habitat?
A desert fox has big ears so there is a larger surface area for energy transfer to take place from the blood.
What factors affect how a substance increases in temperature.
- The amount of energy supplied to it.
- The mass of the substance.
- What the substance is.
Define specific heat capacity.
The amount of energy needed to heat a substance by 1 Kelvin.
What is the unit of specific heat capacity?
Joules per kilogram
What is the equation for specific heat capacity?
c=E/m*θ
Whereby: c=specific heat capacity
E=energy transferred
m=mass
θ=temperature changeHow does a storage heater work?
The heater uses electricity to heat bricks at night.
The bricks have a high SHC so they store lots of energy.
Energy transfer from the bricks keeps the room warm.
How does the mass of an object affect the speed of temperature increase.
The greater the mass, the longer it takes the temperature to increase.
Give five examples of reducing the rate of energy transfer at home.
- Loft insulation
- Cavity wall insulation
- Aluminium behind radiators
- Triple-glazed windows
Explain how loft insulation reduces the transfer of energy.
Fibreglass insulation is a good insulator and air between the fibres stops energy transfer by conduction.
Explain how cavity wall insulation works.
The insulation that is pumped into the cavity is a better insulator than the air it replaces. It traps air in pockets which reduces convection currents.
Explain how aluminium foil reduces the transfer of energy.
The foil is shiny which means it reflects the radiation back inside the house.
Explain how triple-glazing reduce the transfer of energy.
The windows have three glass panes with a vacuum between them preventing convection and conduction. The glass is also a good insulator.
What is used to compare insulative materials?
U-values
What does a u-value represent?
Energy per second that passes through when the temperature diff. is 1*C.
What is the better U-value?
The lower the U-Level, the better insulator a material is.
Explain the properties of a solar panel.
The panel contains liquid filled copper pipes. Copper is used because it is a good conductor. It has a matt black back plate because black is a good absorber and emitter of heat. The liquid is heated on hot days.
How do electrons transfer energy.
When they collide with each other and other atoms
What is infrared radiation?
Energy transfer by electromagnetic waves.
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