Physics: Electromagnetic Waves
The Electromagnetic Spectrum
-All of the waves together are called the electromagnetic spectrum. We group the waves according to their wavelength and frequency: -Gamma rays have the shortest wavelength and highest frequency. -Radio Waves have the longest wavelength and lowest frequency. The spectrum is continuous. The frequencies and wavelengths at the boundaries are approximate as the different parts of the spectrum are not precisely defined. -All electromagnetic waves travel through space at a wave speed of 300 million m/s.
The Electromagnetic Spectrum
-Electromagnetic radiations are electric and magnetic disturbances. They travel as eaves and move energy from place to place. -All electromagnetic waves travel through space (vacuum) at the same speed but they have different wavelengths and frequencies.
Red Shift vs Blue Shift
-Galaxies are large collections of stars. Light observed from distant galaxies has been 'shifted' towards the red end of the spectrum. This is known as red-shift and means that the frequency has decreased and the wave length has increased. -A blue-shift would indicate that a galaxy is moving towards us. We are able to see these effects by observing dark lines in the spectra from galaxies. -The further away the galaxy, the bigger the red-shift. This suggests that distant galaxies are moving the fastest. -All the distant galaxies are moving away from each other, so the whole universe is expanding.
The expanding universe
-Imagine a wave source is moving relative to an observer. The wavelength and frequency of the waves detected by the observer will have changed (shifted) from the original produced by the source. This is called the Doppler Effect. -When the source moves away from the observer, the observer wavelength increases and the frequency decreases. -When the source moves towards the observer, the observed wavelength decreases and the frequency increases. -The Doppler effect can be demonstrated with sound waves.For example, and ambulance siren will sound different depending on whether it is moving away from you (pitch lower) or towards you (pitch higher).
Infrared, microwaves and radio waves
-Infrared radiation is given out by all objects. The hotter the object, the more IR it emits. Remote controls for devices such as TVs and CD players use IR. -Microwaves are used in communication. Microwaves transmitters produce wavelengths that are able to pass through the atmosphere. They are used to send signals to and from satellites and within mobile phone networks. -Radio waves transmit radio and TV programmes and carry mobile phone signals. -Microwave radiation and radio waves penetrate your skin and are absorbed by body tissue. This can heat internal organs and may damage them. -Infrared radiation is absorbed by skin; too much will burn your skin.
Visible Light
-Visible light is the part of the electromagnetic spectrum that is detected by our eyes. We see the different wavelengths within it as different colours. -The wavelength increases across the spectrum from violet to red. We see a mixture of all colours as white light. -Visible light can be used for photography.
The Big Bang
Big Bang Theory (Hubble): -Universe started from a huge explosion from a tiny point. -Universe is expanding. -Predicts cosmic microwaves background radiation. Steady State (Hoile): -Universe has always existed. -Universe is expanding. -Cannot explain CMBR.