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Flashcards by ella stokes, updated more than 1 year ago
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| Question | Answer |
| What type of heat transfer occurs in solids? | Conduction |
| What type of heat transfer occurs in fluids (liquids and gases)? | Convection |
| What is Infra-Red Radiation? | Electromagnetic waves carrying heat energy. |
| What is conduction? | Heated particles gain kinetic energy, bump into each other and pass on kinetic energy. |
| What is convection? | Fluids expand, become warm and less dense, so rise above its colder denser surroundings. Cooler fluids take its place. This makes a circulation of fluids, convection currents. |
| How is conduction stopped? | Gases (like air) - as particles are further apart. |
| How is convection stopped? | Solids - as no solid can flow |
| How is infra-red radiation stopped? | Shiny surfaces usually, but sometimes thick solids or liquids. |
| What does infra-red radiation happen in? | Mainly gases and vacuums. Dark, matte colours are best emitters and absorbers of IR. |
| Which surfaces best emit radiation? | Black, rough surfaces. |
| Which surfaces best reflect radiation? | Shiny, smooth surfaces. |
| Is air a good, or poor conductor? | Air is a poor conductor - it stops conduction as particles are far apart. |
| How does double glazing stop conduction? | Traps a layer of air in between two layers of glass, the air making the particles further apart. |
| How does cavity wall insulation stop conduction and convection? | It has foam between two walls. The foam bubbles stop convection and the air pockets in the foam reduce conduction. |
| What does a vacuum do in terms of heat transfer? | Stops both conduction and convection as there are no particles at all in a vacuum. |
| What is Specific Heat Capacity (SHC)? | The energy needed to heat 1kg of a material by 1°C. |
| What does a low specific heat capacity mean for a material? | - It heats up quickly -It cools down quickly -It stores less energy |
| What is Specific Latent Heat? | The energy that 1kg of material needs to change state. |
| What unit is heat measured in? | Joules (J) |
| What is heat? | Heat is a measure of energy on an absolute scale (J). |
| How is temperature measured? | °C, °F or K |
| What is temperature? | A measure of hotness on a chosen scale. |
| On heating graphs, what do flat areas of constant temperature show? | -A change of state -Bonds between molecules are breaking |
| Describe heat flow. | Heat energy flows from a high temperature to a low temperature. |
| Describe what happens in ovens. | -Heat travels to food by convection and infra-red radiation -Surface particles on food vibrate -Vibration heats up solid food by conduction (or food liquid by convection) |
| Describe what happens in microwave ovens. | -Heat travels to food by microwaves which can penetrate about 1cm under the surface. -Upper layer water molecules absorb microwaves and vibrate. -Vibration heats up rest of solid food by conduction (or liquid by convection). |
| What are thermograms? | Images where different colours represent different temperatures: -White = hot -Purple/Blue = Cold |
| Name the parts of a transverse wave: | 1 - Wavelength 2 - Amplitude 3 - Crest/Peak 4 - Trough |
| What does frequency mean? | The number of waves in 1 second. |
| What is the electromagnetic spectrum going from: High frequency/low wavelength TO Low frequency/high wavelenth | Gamma X-rays Ultraviolet Visible Infra-red Microwaves Radio |
| What are the uses of Gamma waves? | Killing bacteria and treating cancer. |
| What are the uses of X-rays? | Seeing bones. |
| What are the uses of Ultraviolet? | Sun-beds and fluorescent lights. |
| What are the uses of visible waves? | Optical fibers and light bulbs. |
| What are the uses of infra-red? | Cooking, TV remotes and optical fibers. |
| What are the uses of microwaves? | Cooking, satellites and mobile phones. |
| What are the uses of radio waves? | Radios and TV signals. |
| What is total internal reflection (TIR)? | Where light is completely reflected back from a boundary between two materials - because the incident angle is greater than the critical angle. |
| How do optical fibers use TIR? | Thin rods of high-quality glass transmit signals using visible light or infra-red waves. They 'bounce' along the rod by TIR. |
| What is the connection between frequency and energy in waves? | A high frequency wave is a high energy wave - they are usually more dangerous to the human body. |
| What is the connection between darker skin and UV rays? | Darker skins absorb more UV, stopping it reaching the lower layers of tissue and doing damage. |
| Is a higher or lower factor sun cream better for protection against UV rays? | A higher factor is better? |
| What does the factor on sun cream mean? | It tells you how much time longer than normal you can spend in the sun, e.g. factor 10 gives you 10x as long in the sun as usual. |
| What is the connection between UV rays and the Ozone Layer? | The Ozone layer protects the earth from dangerous UV, but CFCs are depleting the layer. |
| What is an analogue signal? Describe its shape. | A continuously variable signal. |
| What is a digital signal? Describe its shape. | A signal with only two states: 'on' (1) or 'off' (0). |
| What are the advantages of digital signals? | -Interference has less effect on the received signal. -The signal is less susceptible to interference -Multiplexing - several signals can be sent at once. |
| What is Morse Code? | Messages consisting of digital signals of light or sound transmitted using 'dots' (.) and 'dashes' (-). |
| How do lasers read CDs? | They read the digital signals of 'bumps' and 'pits' on the bottom of CDs. A bump reflects more light and counts as '1', so the pit counts as '0'. |
| How does wireless technology work? | It uses electromagnetic waves to transmit signals without wires. |
| What is the ionosphere? | A layer of charged particles in the atmosphere. |
| What happens in microwave communication? | Microwaves travel in straight lines and can go through the ionosphere to communicate with satellites |
| How do microwaves lose signal strength? | They lose signal strength when transmitted as the signal spreads out (diffracts). |
| In microwave communication, what happens to signals of similar frequencies? | They can interfere with each other and cause signal loss. |
| What happens in Radio Communication? | Radio waves can reflect off the ionosphere ad can be made to bend (refract) over the horizon if they reach a different layer of the atmosphere |
| In radio communication, what happens to signals of similar frequencies? | They can interfere with each other and cause signal loss. |
| What are seismic waves? | The waves that earthquakes produce. |
| How many types of seismic waves are there? | 2 |
| What are the two types of seismic (shock) waves? | P waves and S waves. |
| Describe P waves. | -Faster than S waves -Longitudinal -Shake ground up and down -Travel through solids and liquids (all of Earth's layers) |
| Describe S waves. | -Slower than P waves -Transverse waves -Shake ground side to side -Travel only in solids (stopped by Earth's liquid outer core) |
| What happens when a substance is heated? | Its particles gain kinetic energy. This energy makes liquid and gas particles move around faster, in a solid, vibrate more rapidly. This is what causes a change in state. |
| What is an absolute scale? | Can't go lower than zero. |
| Why is energy measured on an absolute scale? | There is a limit as to how slow particles can move. |
| What happens if there is a difference in temperature between two places? | Energy will flow between them. |
| The greater the difference in temperature, what will happen to the rate of cooling? | It will get faster. E.g. Coffee cools down quicker in a cold room. |
| Do materials which need to gain lots of energy to warm release: a) lots of energy b) little energy | a) Lots of energy is released on cooling, they can 'store' a lot of heat. |
| What happens in boiling? | When particles have enough energy to overcome their attraction to each other, gas bubbles form in the liquid. |
| What happens in melting? | Heat energy makes particles vibrate quickly until the forces between them overcome and the particles start to move around. |
| What happens in condensing and freezing? | Bonds form between particles which releases energy, so the temperature doesn't go down until it has fully condensed or frozen. |
| What is condensing? | Going from a gas to a liquid. |
| When does convection occur? | When the more energetic particles move from the hotter to the cooler region, taking their heat energy with them. |
| How do immersion heaters work? | Through convection currents - hot on top cold water below heater. |
| Why can't convection happen in solids? | The particles can't move - they just vibrate on the spot. |
| What method of heat transfers do radiators use? | Convection: Warm air rises and displaces cooler air which falls to replace the gap left by rising heated air. |
| How do we get heat from the Sun? | Radiation |
| How is heat radiated? | Infrared waves |
| How is radiation different from conduction and convection? | -Doesn't need a medium to travel through -Can only occur through transparent substances -The amount emitted depends on surface colour and texture. |
| What is the connection between heat and amount of radiation emitted? | The hotter an object gets, the more heat radiation it emits. |
| Does everything emit and absorb heat radiation? | Yes All objects continually emit and absorb heat radiation. |
| What happens to cooler objects with heat radiation? | Cooler objects absorb heat radiation emitted by hotter things, so the temperature increases. You can feel it - e.g. when indoors and the sun shines through a window. |
| What happens to matt black surfaces with heat radiation? | Matt black surfaces are very good emitters and absorbers of radiation. |
| What happens to light-coloured, smooth and shiny objects with heat radiation? | They are poor absorbers and emitters of radiation - they effectively reflect heat radiation. E.g. Some put foil behind radiators to reflect heat back into the room. |
| Which surfaces are poor emitters and absorbers of radiation? | Shiny, light-coloured and smooth objects. |
| Which surfaces are very good absorbers and emitters of radiation? | Matt black surfaces. |
| How do grills and toasters work? | They heat food by infrared (heat) radiation. The heat radiated is absorbed by the surface particles of the food, increasing kinetic energy. The heat energy is then conducted or convected to more central parts. |
| Why do people line their grill pan with shiny foil? | It reflects the heat radiation onto the bottom of the food, so it is cooked more evenly. It also stops the pan getting dirty. |
| What are microwaves? | Electromagnetic waves that have a different wave length to infrared. |
| Why don't you cover microwave food with foil? What is better? | -It reflects the microwaves so that they won't cook -It can cause dangerous sparks inside -Glass or plastic is fine as they can pass through |
| What is another term for wasted? | Transferred |
| What are things that emit energy called? | Sources |
| What are things that transfer/waste/lose energy called? | Sinks |
| What does insulation do? | Ensures that sinks 'drain' less energy. |
| How does insulation both cost AND save you money? | It cots money to buy and install insulation, or buy more efficient appliances, but it saves you money as your energy bills are lower. |
| What is payback time? | The time it takes for the money you've saved on energy bills to equal the initial cost. |
| What is loft insulation? What is it's average payback time? | Fibreglass 'wool' laid across the loft floor reduces conduction through the ceiling into the roof space. 2 years |
| What does a hot water tank jacket do? What is its average payback time? | It reduces conduction. 4 years |
| What is draught-proofing? What is its average payback time? | Strips of foam and plastic around doors and windows stop hot air going out - reducing convection. 7 years |
| How do thick curtains save energy? What are their average payback time? | Reduce conduction and radiation through the windows? 9 years |
| What is its average payback time for cavity walls & insulation? | 18 months |
| What is a cavity wall? | The layers of bricks with a gap between the, which reduce conduction as particles have further to go. |
| What does double glazing stop? What is its average payback time? | Conduction 30 years |
| How are thermograms taken? | With a thermal imaging camera |
| How do thermograms work? | Objects at different temperatures emit infrared rays of different wavelengths which are displayed as different colours. |
| Why are machines useful? | They convert energy from one form to another. E.g. chemical energy (petrol) is turned into KE in cars. |
| What happens to energy that is inputted into a machine? | Some input energy is always lost or wasted, often as heat. |
| What is the link between energy wastage and efficiency? | The less wastage, the more efficient a device is. |
| What is the symbol for wavelength? | λ |
| What do Sankey diagrams do? | Display how much input energy is being usefully employed, compared to how much is wasted. |
| What is a similarity between light and heat waves? | They are both electromagnetic waves. |
| What is the amplitude of a wave? | The length from the rest position to the crest. |
| What is the frequency on a wave? | The number of complete cycles/oscillations passing a certain point per second. |
| What is frequency measured in? | Hz - 1Hz is one wave per second |
| What is a wavelength? | The length of a full cycle of a wave, from crest to crest. |
| 1kHZ (kilohertz) is equivalent to how many Hz? | 1000 |
| 1MHZ (1 megahertz) is equivalent to how many Hz? | 1,000,000 Hz |
| How do waves travel? | Always in a straight line. |
| What happens when waves arrive at an obstacle? | Their direction can be changed - This can happen by reflection. |
| How do we see things? | Reflection of light. Light bounces off objects into our eyes. |
| What is the law of reflection? | Angle of INCIDENCE = Angle of REFLECTION |
| What happens when light reflects off an uneven surface? | The light reflects off at different angles. |
| What happens when light reflects off an even (smooth and shiny) surface? | Reflected at the same angle so you get a clear reflection. |
| What does TIR stand for? | Total Internal Reflection |
| What is TIR dependent on? | -The angle of incidence being bigger than the critical angle -If the ray is traveling through a dense object like glass to a less dense substance like air |
| In reflection... What happens if the angle of incidence is LESS than the critical angle? | Most of the light is refracted into the outer layer, but some of it is internally reflected. |
| In reflection... What happens if the angle of incidence is EQUAL to the critical angle? | The ray would go along the surface, with some internal reflection too. |
| In reflection... What happens if the angle of incidence is GREATER than the critical angle? | No light comes out, It is all internally reflected, i.e.W TIR. |
| When they pass through a gap or pass an object, what do all waves do? | They diffract (spread out) at the edges. |
| What is the amount of diffraction dependent on? | The size of gap relative to the wavelength The narrower the gap, or the longer the wavelength, the more the wave spreads out. |
| In relation to wavelength... How would a narrow gap be described? | One the same size as the wavelength, so whether it is narrow or not depends on the wave. |
| If a gap is much wider than the wavelength, how much diffraction will occur? | Little |
| If a gap is a bit than the wavelength, how much diffraction will occur? | Diffraction only at the edges |
| If a gap is the same size as the wavelength, how much diffraction will occur? | Maximum diffraction |
| Describe the wavelengths of light. Can it be diffracted? | Very small (about 0.0005mm) Yes, but with a very small gap. |
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