Electromagnetic radiations - electric and magnetic disturbances, travel as waves, move energy from place to place
Electromagnetic spectrum - grouped by wavelength and frequency
Gamma rays - shortest wavelength, highest frequency, higher frequency = more energy transferred
Spectrum is continous and boundaries are approximate
Different wavelengths are reflected, absorbed or transmitted differently by different substances and types of surface
All have the same wavespeed through a vacuum = 300million m/s
Link waves to wavelength and frequency - v= f x λ
v - wavespeed - 300000000 m/s
f - frequency - Hz
λ - wavelength - m
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P1.6.2 - Light, Infrared, Microwaves and Radio Wav
Visible light - part of the electromagnetic spectrum, detectable by our eyes - different wavelengths = different colours, used for photography
Wavelength increases across spectrum from violet to red - white light = mixture
Infrared (IR) radiation given out by all objects, hotter = more emitted, remote controls use IR
Microwaves - used in communications, transmitters produce wavelengths able to pass through atmosphere, send signals to/from satellites and within mobile phone networks
Radiowaves - transmit radio/TV signals and carry mobile phone signals
Microwaves radiation and radio waves penetrate skin and absorbed by body tissue - heats internal organs - may cause damage
Infrared radiation absorbed by skin - too much will burn skin
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P1.6.3 - Communications
Alternating voltage applied, radio waves emitted from aerial, fr of radio waves = fr of alternating voltage, when pass over receiver aerial, alternating voltage caused - fr of alternating voltage = fr of radio waves
Radio and microwave spectrum divided into bands - each used differently
Shorter wavelength = more information carried = shorter range = less spread out
Mobile phones - communicate with local mobile phone mast - wavelengths on border between radio and microwaves
Some think radiation of mobile phones may affect the brain
Optical fibres - thin glass fibres used to transmit signals carried by visible light or infrared radiation - signal travels by repeated total internal reflection - useful: carry more information and more secure
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P1.6.4 - The Expanding Universe
Frequency of an object changes as it moves towards a point - Doppler effect
Moves away: wavelength increases, frequency decreases - moves towards: wavelength decreases, frequency increases
Galaxies - large collection of stars
Red shift - light observed from galaxies is shifted towards red end of the spectrum - wavelength increased, frequency decreased - moving away
Blue shift - light shifted to bue end of the spectrum - moving towards us - able to see these effects by observing dark lines in the spectra from galaxies
Further away galaxy = bigger red shift - most distant moving the fastest - true of all galaxies
All distant galaxies moving away from each other: universe is expanding
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P1.6.5 - The Big Bang
Big Bang theory - if the universe is expanding, it must have started with a massive explosion from a very small intial point
If universe began with the Big Bang - high energy gamma radiation was produced - as universe expands, it becomes lower-energy radiation
Cosmic Microwave Background Radiation (CMBR) - scientist found microwaves from every direction in space - the radiation produced by the Big Bang - Big Bang theory is the only theory to explain the exsistance of CMBR
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