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Doppler Effect

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Hari Tank

on 7 July 2011

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Transcript of Doppler Effect

The Doppler Effect and its application in the Hubble Telesope. Who? The revelation of the doppler effect relates to
galaxies, and presents us with a notion of what
is happening in the cosmic environment around us. In 1842 a physist by the name Christian Doppler
proposed this idea in Prague and hence the
"effect" is named after him. After proposing his hypothesis it
was confirmed by Buys Ballot
(a chemist and meteorologist) in 1845. In essence the Doppler effect is the change in frequency of a wave as its source moves. An example of this
is a police car passing you with
its siren ON. If the police car was stationary the waves emitted from the Siren would look like
this. However when the car begins to move/accelerate the waves would look like this... This is the Doppler effect in action. Therefore
when a police car passes by (with the siren on) you here the change in sound. NEEEEEEOWWWWWWW what? This is how it looks in action... However it might not work with this guy (and his police-mobile).
Any ideas why? It probably won't work with the him and his police-mobile
because, he would be moving to slow in his vehicle, meaning the
distortion in the frequency would be small - hence creating a
more subtle effect. This provides us with the knowledge that speed/acceleration
is an important factor relating to the intensity at which the frequency is altered/deformed. This is a graphical snapshot of the effect. Where is the peak(s) and trough(s) of the waves? The lines represent the peaks and the spaces inbetween represents the troughs. Cosmic
Relation However the doppler effect is not
just to do with frequencies changing with sound. In fact, it is mainly to do with light, and the way
it changes as the source it is coming from moves closer
or further from us. Similar to how sound changes due to its frequency light also
changes, this is indicated by colour. You might have noticed the two colours (red and blue) are the two extremes of the colour spectrum. When light is shifted down the spectrum
it is red, meaning it is moving away from us, "Red Shift". When light is shifted up the spectrum it is
blue, meaning it is moving towards us, "Blue shift". Our closest Spiral Galaxy is? Andromeda Blue, meaning it is moving towards us, and infact it is on a collision course with the milky way. Also commonly known as M31 it is ≈ 2.5 million light-years from earth

It can be spotted by the naked eye under the cassiopeia constellation Despite this, all terrestrial life
will have probably ended. However, this goes to show how significant this "effect" is.
It helps us understand what is happening to massive galaxies just by looking at the colour it appears. Edwin Hubble Edwin Hubble was an American
astronomer working in the early decades
the 20th Century. At this time many big telescopes
were being constructed, meaning
thousands of dim galaxys could be
observed. Hubble photographed
these and kept a catalogue of them. He was the first to measure a distance
to another galaxy, confirming there
were galaxies beyond our own and his
work helped establish our universe is
expanding. His great achievement was combining measurements of distance galaxies with their speeds of recession, deduced from their redshifts. He plotted a graph showing v, the recessional speed against x, the distance from us. The pattern was clear, the the distance
to a galaxy, X, the greater the speed of
recession, V. This relationship is known as Hubbles Law,
and we can write it: v = HoX, where the constant of
proportionality Ho is known as Hubbles constant. Hubbles contant also appears the equation 1/Ho, the equation for the approximate age of the universe The faster the source is
receeding, the greater the redshift.
The speed of recession,V, of a
galaxy can be deduced from the
factional change in wave length. We can show that:

Δλ v
__ = __
λ c
(where c = speed of light)

This is the Doppler equation and it can be
re-arranged to show the change in wavelength, as
well as the speed of a galaxy, however it can
only be applied to galaxys travelling slowly
compared to the speed of light (that is v >> c) Although the doppler effect relates
to distant galaxies and stars, one of
its main applications is in the form:
Doppler ultrasonography. It works because the doppler effect occurs
when waves are emitted, reflected or detected
by a moving object. In this case the iron-rich
blood cells are moving along. When a pulse
of ultrasound waves are sent they are partially
reflected back by the cells. The reflected waves
have a slightly different wavelength therefore
this is a useful application of the effect, and it
can be used to create medical scans. By: Hari Tank & Ali Abdulrahman,

Thanks for listening

Visit: physicsdoppler.blogspot.com What colour does Andromeda appear? Who What Cosmic Relation Edwin Hubble
Full transcript