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level: The expanding Universe

Questions and Answers List

level questions: The expanding Universe

QuestionAnswer
what is the doppler effectthe change in frequency observed when a source of sound (or light) waves moves relative to an observer
what happens to sound frequency when a source is moving towards the observerit increases
what is the formula for doppler effectwhere fo is observed frequency in hz fs is source frequency in Hz v is speed of sound waves in ms-1 vs is speed of source in ms-1 (the sign in the denominator is negative if source is moving towards the observer and positive when source is moving away from the observer)
what happens to frequency of sound source moving away from an observerit decreases
what is redshiftan example of the doppler effect in which light from stars or galaxies that are moving away from us is shifted to longer wavelengths
what is blueshiftwhen light from stars or galaxies moving towards us is shifted to shorter wavelengths
what is the formula for redshift when given wavelengthswhere z is red shift (no unit) lambda observed is the observed wavelength of light from the star in metres lambda rest is the wavelength of light emitted by the star measured in metres
what is a negative red shift equivalent toa blue shift
what is the formula for redshift for galaxies moving at non-relativistic speeds (less than ten percent of the speed of light)z=v/c where z is red shift v is the recessional velocity of the galaxy in ms-1 c is the speed of light in metres per second
what is hubbles lawthe further away a galaxy is, the faster it is moving away from us (the higher its recessional velocity) this suggests that the universe is expanding
what is the formula for hubbles lawv=H₀d where v is the recessional velocity of the galaxy in ms-1 Ho is hubbles constant in per seconds (s-1) d is the distance to the galaxy in metres
how do you calculate the age of the universe using hubble's constantt=1/Ho
how much is 1 light year in meters9.46x10^15 m
describe the movement of galaxiesgalaxies rotate around their cores stars within the galaxy rotate with varying orbital speeds stars on the outer arms of a galaxy should travel slower than those closer to the galactic core as they are further from the centre of the mass and therefore experience a smaller gravitational force of attraction
how can the mass of a galaxy be estimatedfrom the orbital speed of the stars within in this is done by measuring the red shift and blueshift of the light coming from the stars
what is unusual about the orbital speed of stars within galaxies?stars in the outer parts of galaxies are moving far faster than they should for the mass that is visible to us for the mass we can observe, the stars should escape the gravitational pull of the galaxy and fly into space, but something is preventing them from doing so astronomers concluded that there must be a considerable amount of matter in galaxies that we cannot see, called dark matter
what do recent observations of the redshift of distant galaxies show is happening to the rate of expansion of the universeit is increasing
what evidence is there that there is an unknown force acting against gravitational attraction?the rate of expansion of the universe is increasing which contradicts the idea that gravity should be an unbalanced force acting to slow down this expansion this source of energy capable of producing this force has not yet been determined and is simply called dark energy
what was the big banga rapid expansion of the universe from a singularity our universe is thought to have begun as an infinitesimally small infinitely hot infinitely dense singularity after its initial appearance the universe inflated , expanded and cooled, going from very small and very hot to the size and temperature of our current universe it continues to expand and cool to this day
what does the colour of a star tell usthe surface temperature of that star with red being the coolest and blue being the hottest
what type of radiation do stars emitelectromagnetic radiation over a wide range of wavelengths
what information can we see from a intensity of emitted radiation/wavelength graph for stellar objectsgraph has a blackbody curve stellar objects emit radiation over the complete electromagnetic spectrum each stellar object has a peak wavelength that depends on its temperature
what is the relationship between the temperature of a star and the radiation emittedas star temperature increases there is more radiation emitted per unit surface area per unit time area under curve on graph increases as star temperature decreases the peak wavelength shifts to a shorter wavelengths
how does redshift and hubbles law provide evidence for the big banghubbles law suggested that galaxies are moving away from us and each other and therefore the universe is expanding light from these distant galaxies would become more stretched out which mean light would shift towards red if we were to go back in time there must have been a moment where the universe was a single point
how does cosmic microwave background radiation provide evidence for the big bangbackground radiation comes from all directions in space originally this radiation was at a much shorter wavelength but the expansion of the universe caused the wavelengths to increase over time, and the peak wavelength is now in the microwave part of the spectrum
how does the temperature of the univeerse provide evidence for the expansion of the universeas the universe expanded it also cooled down and now has a temperature of 2.7K (almost absolute 0)
how does the relative abundance of hydrogen and helium provide evidence for the expansion of the universealthough the big bang produced helium and lithium, all elements heavier than lithium can only be made by thermonuclear reactions in stars the relative proportions of the elements that we observe today, helium, hydrogen, and other light elements, correspond to what is predicted if the universe started around 14 billion years ago.
light coming from galaxies is red shifted. explain why this gives evidence of the big bangred shift is evidence that the universe is expanding expanding universe is evidence that supports the big bang theory