# As Science OCR Unit 1 Module 1

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What is diffraction
A process in which waves spread out after they pass an obstacle or gap in a barrier
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What is reflection
A process in which light bounces back office smooth surface
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What is refraction
A process in which the direction of light changes when it crosses a boundary between two surfaces which have different densities
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Evidence that light is a wave
Light refracts, diffracted, polarises
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what is white light made of
range of wavelengths of visible light
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what is a rod cell
They respond to the whole frequency range of visible radiation, this only allows a black-and-white image to be perceived
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What is it Cone cell
Responds more strongly to particular frequency ranges, e.g green can be seen when green cells stimulated strongly and red and blue weakly
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what is Wavelength
Length of a complete waveform, measured in metres (m)
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What is frequency
The number of complete wavelengths passing a point in one second, measured in hertz (Hz)
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What is speed
how fast something is traveling, measured in metres per second (ms )
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what is equation for speed inc. units
C=fλ speed(ms )= frequency(Hz) x wavelength (m)
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transfer of energy from the sun to the earth through a vacuum
some solar radiation passes through atmosphere, some reflected, earth transmits IR, so temp of earth stable at around 290K
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transfer of energy by Absorption by pigment
absorb some wavelengths of visible light more strongly but reflects others like chlorophyll reflects green so looks green
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transfer of energy between radiant heaters and surrounding area
Radiant heaters rely on the fact hot objects emit IR which is easily absorbed by surfaces of the room
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Transfer of energy by the human body
Naked human body emits IR at 500 W, in enclosed space body absorb energy at rate of 400w, clothes worn to reduce energy losses by 100w and to keep balance between absorption and emission
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how image is formed
1)light reflected off where you want to take picture, 2) light refracted by lens onto sensor 3) sensor absorbs light and transfers into electrical energy
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limitations of image
light not perfectly refracted by lens, small aperture may diffract some light
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Effect of gamma and x rays on human body
high frequency= highest energy, can ionise cells and cause cancer
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Effect of UV radiation on human body
when absorbed by skin can cause chemical bonds to break, can cause cancer
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Effect of Microwaves on human body
causes rapid heating of water molecules
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Effect of radio waves on human body
believed to cause no or little harm to the human body
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Use of microwaves
signal for mobile phones
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use of IR
in remote controlled devices to turn electronic equipment on and off
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use of UV
in optical fibres
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How do Thermal IR images show temp?
detects how much thermal IR is emitted by the object, white=high relative temp
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How do NIR show vegetation and water
Vegetation reflects NIR very well and Water absorbs NIR really well
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How does radar show roughness of an object
measures amount scattered
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How does absorption by the atmosphere limit RS images
UV absorbed by ozone and IR by CO2 and water vapour
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How does scattering by the atmosphere limit RS images
blue light scattered by Nitrogen, Drops of dust and rain can scatter green and red light
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How does reflection limit RS images
clouds prevent Visible and IR reaching satellite because are reflected back to surface of earth
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How does pixel density limit RS images
resolution determines but area represented by a single pixel, so small objects may be to small and blurred to identify
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how does the eye limit sensitivity of image
rod cells 1000 times more sensitive than cones. brain produces image in low light, e.g moonlight. but rods are more sensitive to green e.g. so lawn is lighter than red and blue objects on the dark
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how is CCD different to photographic film
CCD can respond to any frequency of light. Filters can be used on CCDs to remove certain wavelengths of light, e.g a yellow filter to remove yellow light.
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## Other cards in this set

### Card 2

#### Front

What is reflection

#### Back

A process in which light bounces back office smooth surface

### Card 3

#### Front

What is refraction

### Card 4

#### Front

Evidence that light is a wave

### Card 5

#### Front

what is white light made of