P1b AQA Revision Notes

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P1b revision
Electromagnetic waves
Electromagnetic waves are electric or magnetic disturbances that transfer energy from one place to
another
The amount of energy transferred depends on the wave length
The wave length is the distance from one wave peak to the next wave peak along the waves
The frequency is the number of complete waves passing past a point per second
All electromagnetic waves travel at 300 million ms1 in a vacuumcan be substituted for wave speed
Wave speed (ms1) = frequency (Hz) x wavelength (m)
Gamma Radiation
o Can be used to kill harmful bacteria
o Sterilise surgical instruments
o Kill cancer cells
Narrow beam is directed at the tumour
Beam is aimed at it from different directions to kill the tumour and not the surrounding
tissue
Surrounded by thick lead container
o High doses kill living cells
o Low doses cause cell mutation and cancerous growths
o Film badge
Light
o Light from lamps and the sun is called white light because it has all the colours of the spectrum in
it
o Human eye doesn't detect ultraviolet or infrared
Ultraviolet radiation is electromagnetic radiation between violet light and xrays in
wavelength
o Ultraviolet light makes some chemicals emit light
o Ultraviolet light is harmful to the eye
o Electromagnetic waves directed at substances (incident waves)
The surface of the substance and wavelength can determine whether the waves are totally,
partially or not reflected at all
Light on glass are partially reflected
Xrays directed at plastic are not reflected at all
Some waves are absorbed by the substance ­ would increase the temperature ­ could
create alternating current
Waves that are not reflected or absorbed are transmitted ­ substance and wavelength
depend on whether a wave is transmitted or not
UV is mostly absorbed by glass
Xrays mostly pass through tissue but is absorbed by bone
Infrared
o All object emit infrared
o The hotter the object, the more infrared it emits
o Infrared is absorbed by the skin ­ kills/damages skin cells ­ heats up the cells
o Devices
Heaters
Infrared scanners/cameras
Optical fibres

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Remote control handsets
Microwaves
o Shorter in wavelength that radio waves
o Lies between radio waves and infrared radiation
o Used for
Communications ­ can pass through the atmosphere ­ don't spread out as much as radio
waves
Heating food in microwaves ­ unlike infrared, microwaves penetrate food
Radio Waves
o Range from 300 000 Hz to 3000 million Hz
o Longer in wavelength
o Lower frequency
o Used for
Radio waves emitted from an aerial when an alternating current is passed through it ­…read more

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Can carry much more
information
o More secure
Analogue and digital signals
o Digital Signals ­ sequence
of impulses ­ voltage level
is either high (1) or low (0)
­ mobile phone and
computer signals are digital
o Analogue signal ­ a wave
that varies in amplitude or
frequency between 0 and
its maximum value
o Waves used to carry waves
are called carrier waves
o To send a digital signal
Pulses are used to
switch the carrier
signal on and off
Digital radio
transmitters,…read more

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Alpha radiation (helium nucleus) is stopped by paper
Beta radiation (fastmoving electron) when through the paper
Gamma Radiation is more penetrating than beta
Most atoms have a stable nucleus that doesn't change
o Radioactive atoms have a nucleus that is unstable that emits alpha, beta or gamma radiation
o Unstable nuclei decay when they emit radiation
o Uncertain when a nucleus will decay ­ random event
Geiger counter used to find out how far radiation can travel through air
Radiation Absorber materials Range in air…read more

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Radioactive dating
Carbon dating
Used to find the age of ancient wood
Living wood has a tiny proportion of radioactive carbon ­ half life of 5600 years
Uranium dating
Used to find the age of igneous rocks
The rocks contain radioactive uranium ­ half life for 4500 million years
Uranium atom decays into lead
The origins of the universe
Red shift ­ light waves stretched if the star or galaxy is moving away from us ­ red end of spectrum
Blue shift ­ light waves…read more

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