8/8/2019 Phys1b AQA Revision Aid

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All EM waves travel through space at speed oflight (300 million m/s).

Wave speed= Frequency X Wavelength(m/s) (Hz) (m)

X-rays and gamma rays are absorbedby dense material such as bone andmetal but pass through soft tissue

X-rays and gammarays damage livingtissue when theypass through it.

Large doses can killcells, small dosescan cause cancer

Gamma raysHave the shortestwavelengths used to killbacteria in food,sterilise surgicalequipment and killcancer cells.

Ultraviolet-UVFound naturally in sunlight.UV harms the skin andeyes, causes a sun tan, usedin security markers

Radio waves arereflected by the

IONOSPHERE.Stronger insummer

Analogue signals varycontinuously in amplitude orfrequencyDigital signals are on or off.Digital signal free ofinterference and carry moreinformation.Carrier waves (radio,microwaves etc) carriesdigital/analogue signal

Infrared-IRAll objects emit IR. The hotterthe object the more IR it emitsIR heat objects.Uses: heaters, IR scanners, IRcameras, remote controls, opticalfibres and communications

Optical FibresVisible light and IR carrysignalsCarry more info than wiresMore secure, signal stays in

wire

MicrowavesShort wavesCan pass throughatmosphere for satellitecommunicationsUsed in cooking, microwaveovens - heat water molecules

Radio wavesHave the longest wavelengthsUsed in communicationsRadio waves - smallest long waves -300,000Hz+Carry radio, TV, mobile phone signals

Alternating voltage ariel receiverFrequency of radio wave = alternatingvoltage of carrier waveHigh frequency radio waves-

Carry more informationHave a shorter rangeLess diffraction

X-rays are usedin hospitals totake radiographs.

The use ofradio wavesdepends onthe frequency

of the waves

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8/8/2019 Phys1b AQA Revision Aid

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Marie Curie-DiscoveredRadioactivity.Worked withuranium. Died ofcancer becauseof her work.

Unstable radioactive elements decayrandomly and give off particlesIsotope atoms of an element havedifferent numbers of neutrons

Detect radiation with Geiger MullerTube (GM tube)

Alpha Radiation- Stopped by paper or a

few cm of airBeta Radiation Stopped by thin aluminiumor about 1m of airGamma radiation- Stopped by thick lead orconcrete and has an unlimited range in air

Alpha particlePositive charge, deflected in magnetic andelectric fields, Helium nucleusBeta particleNegative charge, deflected in magneticand electric fields, electron emitted fromnucleusGamma particlesNo charge, not deflected in magnetic andelectric fields, EM wave

Ionisation- Alpha and beta particlesknock electrons out of atoms

Uses of radioactivityAutomatic thickness monitoring- uses betaRadioactive tracers- uses gammaRadioactive carbon/uranium datingCarbon- woodUranium- rocksSmoke detectors- uses alpha

Light from distant galaxy is red-shifted to longer wavelengthsEdwin Hubble discovered that lightfrom galaxies were red-shiftedDistant galaxies are moving awayfrom usSpeed of distant galaxy isproportional to distance from usThe universe is expanding

Big Bang (BB)TheoryMassive explosion from asmall pointBackground microwaveradiation is radiationcreated just after the BB.Created as high energygamma radiation after BBAs universe expanded, itstretched into longer and

longer wavelengths.

The Earths atmosphereabsorbs all electromagnetic

waves, except visible light,radio waves and some UVradiation.Satellite detectors are usedto make observations outsidethe visible and radio spectrum.Clear images are observedusing telescopes on satellitesdetecting visible light.

Half lifeTime it takes for number ofradioactive nuclei of the isotope todecay to half its initial value.

P1b Physics

A radioactive substancecontains unstable nuclei.An unstable nucleusbecomes stable byemitting radiation.

The most distant galaxies areabout 13 million light years away.

Space, time and matter createdby the Big Bang

BIG BANG happened 13,000million years ago

IsotopesDifferenttypes ofatoms ofthe samechemicalelement,each having

a differentnumber ofneutrons