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28 Cards in this Set
- Front
- Back
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Energy flow
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Energy in the form of heat, flows from a warmer to a colder body. When energy flows away from a warm object, the temperature of that object decreases.
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Temperature
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Temperature is a measure of 'hotness' and allows one object to be compared to another.
Temperature is measured on a ARBITRARY scale: you don't need a thermometer. A thermogram uses colour to show temperature. Hot is YELLOW, cold is BLUE. Heat is a measurement of INTERNAL ENERGY and is measured on an ABSOLUTE scale. When an object is heated and it's temperature rises, energy is TRANSFERRED. |
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Specific heat capacity
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- SHC is the energy needed to raise the temperature of 1kg of a substance by 1°C.
- Measured in joule per kilogram degree celsius (j/kg°C) - It's different for different materials - The formula for SHC is: ENERGY TRANSFERRED= MASS X SHC X TEMPERATURE CHANGE |
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Specific latent heat
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- SLH is the energy needed to melt or boil 1kg of the material.
- Measured in joule per kilogram (J/kg) - Different for different materials and each of the changes of state. - The formula for SLH is: ENERGY TRANSFERRED= MASS X SLH When the object is heated and it changes state, energy is transferred. When a substance changes state, energy is needed to break the bonds that holds the molecules together. This explains why there is no change in temperature. |
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Energy
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Different types of insulation cost different amounts of money.
Most energy is lost from the walls of an uninsulated house. PAYBACK TIME= COST OF INSULATION/ ANNUAL SAVING Different energy sources each have their advantages and disadvantages. Cost can be compared by using a consistant unit- kWh. ENERGY EFFICIENCY= USEFUL ENERGY OUTPUT/ USEFUL ENERGY INPUT |
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Energy can be transferred by:
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- CONDUCTION through solids, e.g Brick
- CONVECTION by movement of air, e.g in a cavity wall - RADIATION across a space without the need for a material, e.g foil behind a radiator. (Radiation goes from a high temperature to a low temperature) |
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House insulation: Double glazing
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DOUBLE GLAZING reduces energy loss by CONDUCTION. the gap between the two pieces of glass is filled with a gas or contains a vacuum.
SOLIDS are good conductors because the particles are close together. They can transfer energy very easily. Particles in a gas are far apart, so it's very difficult to transfer energy. There are no particles in a vacuum so it's impossible to transfer energy by conduction. |
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House insulation: Loft insulation
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Reduces energy loss by CONDUCTION and CONVECTION.
- Warm air in home rises - Energy transferred through the ceiling by conduction - Air in the loft is warmed by the top of the ceiling - the warm air is trapped in the loft insulation - Both sides of the ceiling are at the same temperature so no energy is transferred. Without Loft insulation: - The warm air in the loft can move by convection and heat the roof tiles - Energy is transferred to the outside by conduction |
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House insulation: Cavity wall insulation
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Reduces energy loss by CONDUCTION and CONVECTION.
- The air in the foam is a good insulator. - The air cannot move by convection because it's trapped in the foam. INSULATION BLOCKS used to build new homes have shiny foil on both sides so: - Energy from the sun is reflected back to keep the home cool in summer - Energy from the home is reflected back to keep the home warm in winter. |
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Energy transfer
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CONDUCTION is due to the transfer of KINETIC ENERGY between particles.
A gas expands when it's heated. This makes it less dense so it rises. DENSITY= MASS/ VOLUME The unit of density is kg/m3 or g/cm3. Radiation doesn't need a material to transfer energy so energy can be transferred through a vacuum. |
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Radiation
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INFRARED RADIATION doesn't penetrate food easily but microwaves penetrate up to 1cm into food.
Microwaves can penetrate glass or plastic but are reflected by shiny metal surfaces. The door of a microwave is made from special reflective glass. MICROWAVE RADIATION is used to communicate over long distances. The transmitter and reciever must be in LINE OF SIGHT. Aerials are normally situated on the top of high buildings. Satellites are used for microwave communication. The signal from Earth is recieved, amplified and re-transmitted back to Earth. Satellites are in lone of sight because there are no abstacles in space. The large aerials can handle thousands of phone calls and television channels at once. |
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Electromagnetic Spectrum (USE DIAGRAM) pg 7
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Energy is transferred by waves.
- The amount of energy depends on the frequency or wavelength of the wave. - High frequency (Short wavelengths) waves transfer more energy. - GAMMA WAVES transfer the most and RADIO WAVES the least. NORMAL OVENS cook food by INFRARED radiation. Energy is absorbed by the surface of the food so the KINETIC ENERGY of the surface food particles increases. The rest of the food is cooked by CONDUCTION. Microwave ovens cook food by MICROWAVE radiation. the water molecules in the outer layers of food vibrate more. Energy is transferred to the rest of the food by CONDUCTION and CONVECTION. |
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Microwave properties
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Microwaves have wavelengths between 1mm and 30cm.
Mobile phones use longer wavelengths than microwave ovens. This means less energy is transferred by mobile phones. Microwaves don't show much DIFFRACTION around natural objects such as hills. Therefore the signal strength for mobile phones can change a lot over a short distance. Mobile phones can interfere with sensitive equipment so they are banned on planes and in many hospitals. |
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Signals
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DIGITAL signals have two values- ON and OFF.
ANALOGUE signals can have any value and are continuously variable. The analogue signal changes both it's amplitude and wavelength. Before an analogue signal is transmitted, it's added to a CARRIER WAVE. The frequency of the carrier wave is usually higher and the combined wave is transmitted. INTERFERENCE from another wave can also be added and transmitted. if the wave is amplified, the interference is also amplified. Interference also occurs on digital signals but isn't apparent because it only has two values. MULTIPLEXING allows a large number of digital signals to be transmitted at the same time. |
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Total internal reflection and Critical angle (DIAGRAM) pg 8
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When light travels from one material to another, it's refracted.
If light passing from a more dense material into a less dense material, the ANGLE OF REFRACTION is larger than the ANGLE OF INCIDENCE. |
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Total internal reflection and Critical angle 2 (DIAGRAM)
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When the angle of refraction is 90 degrees, the angle of incidence is called the CRITICAL ANGLE.
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Total internal reflection and Critical angle 3 (DIAGRAM)
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If the angle of incidence is BIGGER than the critical angle, the light is reflected. This is TOTAL INTERNAL REFLECTION.
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Optical fibres
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telepohone conversations and computer data are transmitted long distances along optical fibres. Some fibres are coated to improve reflection.
An endoscope allow doctors to see inside the body without the need for surgery. Light passes along one set of optical fibres to illuminate the inside of the body. The light is reflected and passes up another set of fibres to an eye piece or camera. |
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Radio refraction
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Radio waves are refracted in the upper atmosphere.
The amount of REFRACTION depends on the frequency of the waves. There's less refraction at higher frequencies. |
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Diffraction
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When waves pass through a gap they DIFFRACT. The amount of diffraction depends on the width od the gapcompared to the wavelength. MOST DIFFRACTION occurs when the GAP width is SIMILAR to the wavelength.
Radio waves diffract around such things as mountains. The longer the wavelength, the more the diffraction. LONG WAVE SIGNALS DIFFRACT BUT SHORT WAVE AND MICROWAVE SIGNALS DON'T. |
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Reflection
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Radio waves are reflected from the IONOSPHERE. Water reflects radio waves but land mass doesn't.
Continued reflection by the ionosphere and the oceans allows radio waves to be recieved from an aerial that isn't in the line of sight. MICROWAVES pass through the ionosphere. They're recieved by orbiting satellites, amplified and re-transmitted back to Earth. Communication satellites orbit above the equator and take 24 hours to orbit Earth. |
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Communication Problems
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Radio stations broadcast signals with a particular frequency. The same frequency can be used by more than one radio station because the distance between the stations means thatn only one will be recieved. However in unusual weather conditions, the radio waves can travel further and the broadcasts INTERFERE.
Refraction in the atmosphere needs to be taken into account when sending a signal to a communications satellite. The transmitting aerial needs to send a FOCUSED BEAM to the satellite because it's aerial is very small. The transmitted beam is slghtly deivergent. Some energy is lost from the edge of the transmitting aerial because of DIFFRACTIOn. |
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Light (USE DIAGRAM) pg 10
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The FREQUENCY of a wave is the NUMBER OF COMPLETE WAVES passing a point in one second.
The formula for wave speed is: WAVE SPEED= FREQUENCY X WAVELENGTH |
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Sending messages
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MORSE CODE uses dots and dashes, or flashes of light.
When a signal is sent by light (3x 10^8m/s), electricity, microwaves or radio, it's almost instantaneous. Each method of transmission has dis/advantages: - Can it be seen by others? - How far does it travel? - Can wires be cut? WHITE LIGHT is made up of different colours of different frequencies OUT OF PHASE. LASER LIGHT is at one frequency and IN PHASE. |
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Earthquake waves
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The FOCUS is where the earthquake happens below the surface. The EPICENTRE is the point on the surface above the focus.
L WAVES travel around the surface of Earth. |
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P waves
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P WAVES are LONGITUDINAL pressure waves:
- P waves travel through the Earth at between 5km/s and 8km/s - P waves can pass through solids and liquids P waves travel through the Earth and are refracted by the core. The paths taken by P waves mean that scientists can work out the size of the Earth's core. |
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S waves
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S WAVES are TRANSVERSE waves:
- S waves travel through the Earth at between 3km/s and 5.5km/s - S waves can only pass through solids. S waves aren't detected on the opposite side of Earth because they won't travel through liquid. This tells scientists that the Earth's core contains liquid. A SEISMOGRAPH shows the different types of Earthquake wave. |
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Weather Effects
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NATURAL EVENTS and HUMAN ACTIVITY affect our weather.
- Dust from volcanoes reflects energy from the sun back into the atmosphere making it cooler on Earth. - Dust from factories reflects radiation from towns back to Earth making it warmer on Earth. ULTRAVIOLET LIGHT on the skin causes the cells to make MELANIN, a pigment that produces a tan. People with dark skin don't tan easily because the ultraviolet is filtered out. Use sunscreen with a high SPF (Sun Protection Factor). The formula for the safe length of time to spend in the sun is: SAFE LENGTH OF TIME= PUBLISHED NORM BURN TIME X SPF OZONE is found in the STRATOSPHERE. Ozone helps to filter out ultraviolet radiation. CFC GASES from aerosols and fridges destroy ozone and reduce the thickness of the ozone layer. |
