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waves (sound waves (eardrum vibrates (sound waves reach eardrum causing it…
waves
sound waves
caused by vibrating objects- vibrations are passed through the surrounding of the medium as a series of compressions and rarefactions
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eardrum vibrates
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human hearing is limited by size and shape of the eardrum as well as the structure of the parts of the ear that vibrate
reflect or rarefract
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sound waves refract when they enter a different medium, wl changes but frequency stays the same so speed also changes
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more uses of em waves
visible light
fibre optic cables contain thin optical wires (plastic) that carry data over long distance pulses of visible light
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ultraviolet
fluorescence is uv in some chemicals causing them to glow, radiation is absorbed, light is emitted
fluorescent lights generate uvr, absorbed and reemitted as visible light by a layer of phosphorus- energy efficent
security pens- under uv light the writing glows, otherwise invisible
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xrays
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xrays pass through felsh not bone, amount of radiation absorbed gives image
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gamma
medical tracers - gamma source is injected and its progress around body is followed, can pass out of body to be detected
experiments with waves
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waves on strings
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2) adjust frequency on signal generator until there is a clear wave on the string -frequency needed depends on masses used, length of string between pulley and deducer
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reflection
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specular or diffuse
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diffuse is caused by normal being different for each ray so angle of incidence and reflection are different for each ray
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dangers of em waves
harmful to people
low frequency waves do not have much energy, not absorbed
high frequency (uv) transfer lots of energy, cause damage
uv- damages surface cells (sunburn). xrays/ gamma (ionizing radiation)- gene mutation, cancer
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visible light
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colour filters
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filters that aren't for primary colours let through both wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour
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em waves and their uses
microwaves
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for satellite tv the signal from transmitter is transmitted into space where it is picked up by satellite receiving dish which then transmits the signal back to earth in a different direction. where it is recivfeved by a stalite dish on the ground - slight delay due to long distances
microwave ovens
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waves penetrate few cm of food before being absorbed and transferring energy to water molecules in food, causing it to heat up
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infrared radiation
given out by hot objects, hotter the object the more it gives out
infrared cameras monitor temp, camera turns IR into electrical signal which is displayed as a picture - hotter object, brighter it is on screen
electrical heaters
contains long piece of wire which heats up when current passes through it which emits IR - the IR is absorbed by objects whose heat energy stores increase
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black body radiation
ultimate emitters
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all objects emit em waves due to heat energy stores but perfect black body are the best possible emitters
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as temp of object increases, intensity of each wl emitted increases
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images and ray diagrams
real or virtual
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virtual= when rays are diverging so light from object appears to come from a completely different place (magnifying glass)
size, upright or inverted, real or virtual