Physics 1

HideShow resource information
• Physics 1
• heat and temperature
• heat- is a measure of energy and is measured in Joules
• temperature - is a measure of how hot or cold an object is and is measured in degrees c
• particles stop vibrating at absolute zero or -273 degrees c
• the difference in temperature between an object and its surroundings affects the rate at which energy is transferred. when temperature difference is greater, the rate of energy transfer is higher.
• thermogram show temperature with colours. red is hot, blue is cold. thermogramsare usually used for: security, night vision and studying the earth.
• specific heat capacity
• specific heat capacity is the energy needed to raise the temperature of 1kg of a substance by 1 degree c
• the energy needed to change the temperature of a body depends on
• the material its made from
• the mass (or amount) of the material
• the temperature change of the body
• energy= mass x specific heat capacity x temp change
• specific latent heat
• specific latent heat is the amount of energy (J) needed to change the state of 1kg of a substance
• energy= specific latent heat x mass
• the specific heat of fusion (melting) is not the same value as the specific latent heat of vaporisation (boiling)
• heat energy transfers
• conduction
• metals are good conductors. this is because metals are made of metal ions and free electrons. these ions vibrate constantly. the hotter the metal becomes, the more energy transferred meaning the more kinetic energy the particles have. this energy travels from the hotter parts of the metal to the cooler ones, via free electrons
• there is another way of transferring energy in a metal. metals have electrons that are free to move through. the free electrons gain more kinetic energy as the metal gets heated from collisions. they transfer the energy quickly as they travel through the metals.
• convection
• convection currents only happen in liquids and gasses (fluids). as the fluid is heated, the particles become less dense and rise, pushing the more dense, colder particles down. as the hot particles become cold they become more dense and sink, where they are heated again. this is called a convection current.
• every object emits and takes in infrared radiation. the hotter the objects the more infrared it emits. radiation is able to  work in a vacuum like space. this is why we feel the heat off the sun.
• analogue and digital communications
• an analogue signal values are always changing
• a digital signal is on or off. it only has 2 values represented by 0 and 1
• any interference can be easily removed, as it is easy to tell if its on or off
• many different digital signals can be sent at once. this is called multiplexing. this means more channels on your TV
• more stations available
• less chance of interference
• not all of the UK is covered
• sound quality is poor due to sound being compressed
• Infrared radiation is used in remotes because it can send information/ communicate over short distances. it flashes on/off, sending a sequence which the TV can use to change volume etc. only certain codes with certain devices.
• insulation
• examples of insulators
• air
• clothing
• plastic
• wood
• an insulator slows down the rate of energy transfer
• payback time= cost/ savings per year
• ways to reduce energy transfer in buildings
• loft insulation
• double glazing
• curtains
• draught  excluders
• carpets
• wall cavity insulation
• houses transfer energy to their surroundings. energy flows from hot to cold. from the heat source (house) to the cold sink (surroundings). by insulating a home you reduce energy loses through conduction, convection and radiation
• cavity wall insulation
• the outside walls of a house are two walls with a cavity between them.
• the air is a goof thermal insulator and a poor conductor. however the air inside the walls can move around and transfers heat from the inner wall to the outer via conduction
• the cavity is filled with an insulating material. this contains small pockets of trapped air. this makes use of air as a good conductor, but prevents loss of heat though convection as the air can't form a convection current.
• all objects emits some thermal radiation.
• some surfaces are better at emitting thermal radiation than others
• matt black surfaces are the best emitters of radiation, shine surfaces are the worst.
• matt black surfaces are the best absorbers of radiation. shine surfaces are the worst because they reflect most radiation.
• useful energy and efficiency
• efficiency= (useful energy output/ total energy input) x 100
• snaky diagrams show the energy used and wasted
• waves and our atmosphere
• suncream protects skin from UV radiation, by absorbing the UV rays, protecting the skin underneath
• higher SPFs means the more UV rays absorbed so you can stay out longer.
• the ozone layer protects us from UV radiation, by reflection the rays away from the earth, though some still get through.
• the ozone layer depleted due to chemicals released in the atmosphere from CFCs. it allowed ore radiation to enter the earths surface which could be dangerous.
• using light
• lacers have a straight beam of light, so they are used for surgery, guiding weapons, CDs, DVDs, cutting materials.
• light from lacers all have the same frequency so they are in sync. the light is in phase. this is why lasers are a source of coherent monochromatic light. l;acer light does not speed out so has a low divergence.
• we used lacers to read CDs. there are billions of pits on CDs, as the disc spins a lacer reflects off the surface. when the lacer enters a pit, there is no reflection. the detector reads a series of light pulses, like its morse code.
• electromagnetic waves and wave experiments
• electromagnetic waves all travel at the speed of light in a vacuum.
• the law of reflection states that the angle of incidence is always equal to the angle of reflection.
• as waves go from ne medium to another they can be refracted. as they enter a different medium their speed changes, and causes them to change direction. if the wave slows down, it bends towards the normal if it speeds up it bends away from the normal. this is called refraction.
• diffraction occurs when a wave passes through a gap or past an obstacle. the size of the gap relative to the wave length affects how much diffraction takes place. in general, the longer the wave length or the smaller the gap, the greater the diffraction. the strongest diffraction occurs when the gap is the same size as the wavelength.
• diffraction causes problems when using optical instruments like microscopes and telescopes. when the light enters the instrument it passes through a small gap and diffracts a little. this can lead to a blurred image or a loss of detail.
• wave properties
• total internal reflection. if light hits the boundary between the glass and the air at a big enough angle of incidence, all light stays within the glass; its reflected internally.
• refraction doesn't happen after you pass the critical angle
• when you pass the critical angle, the light is only totally internally reflected, when the angle of icidene is larger than the critical angle.
• optical fibres.
• are used in communications, to carry signals
• are used in medicine to look inside the body.
• an endoscope is made of a bunch of optical fibres to carry light into and out of the body. waves travel along the fibre by total internal reflection. they enter the fibre and hit the edge of the angle greater than theocratical angle,. they reflect to the other end.
• wireless communication
• no wires are needed, so devices can be portable
• radio waves are refracted by different layers in the earths atmosphere. this leads to reduction in the signal, making it difficult for them to be revived over long distances
• microwaves are not refracted, so they are used for sat alit communications
• wireless signals can be reflected off buildings and other large objects. this means that signals can be received even if the receiver is not in direct sight of the transmitter. but it can cause ghosting on television pictures
• diffraction allows low frequency radio waves to be received being hills.
• the lowest frequency radio waves are also from an electrically charged upper layer of the atmosphere, called the ionosphere. meaning they cab reach receivers that are out of sight.
• infrared
• infrared sensors can detect body heat. this means they can be used as burglar alarms.
• infrared is used in remotes. the light flashes on and off, sending a digital signal sent from the remote in a code. a special sequence changes the tv channel. only certain codes work for certain objects.
• the minimum size of a receiver depends on the wavelength of the wave.
• long wave length = large receiver
• this is due to diffraction, when a wave enters a receiver it passes through a gap, if the wave is diffracted it speeds out and you lose detail.
• the amount of diffraction is affected by the size of the gap compared to the wavelength.
• the bigger the receiver compared with the wavelength of wave being received, the less diffraction.
• different telescopes are used to collect different EM waves
• bigger telescopes have less diffraction.
• telescopes that are small have limited resolving power so they are diffraction-limmitted.
• radio telescopes are often linked together so their signals are combined to get more detailed information. a bigger receiver can also collect more EM waves, giving a more intense image.
• humans and the environment
• UV rays can damage the DNA in your cells (cancer)
• darker skin is more protected because it absorbs more UV rays, preventing damage to venerable tissue deep in the body.
• An SPF of 15 means you can spend 15 times as long as you can with out sun cream.
• the ozone layer absorbs some UV rays, however the layer is thinning due to the use of CFCs, that react with oxygen . there is a whole over antartica sure to CFCs so an international an has been placed.
• seismic waves
• p-waves are longitudinal
• p-waves travel through solids and liquids, they are faster than s-waves
• s-waves are transverse
• only travel through solids, and are slower than p-waves
• what do waves tell us?
• half way  through the earth p-waves change direction, suggesting theres a change of properties as you go from mantle to core.
• s-waves can't be detected as they only trade through solids.