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AS and A Level: Waves & Cosmology
210 AS and A Level Waves & Cosmology essays
- Peer Reviewed essays 20
The candidate’s introduction starts well, it is interesting and they have attempted to engage the reader by stating that the imbalance between matter and antimatter is unusual and goes against…
- Essay length: 1111 words
- Submitted: 16/02/2009
- Reviewed by: pictureperfect 08/07/2012
The author has responded well to the task, by developing a suitable experiment to measure how the voltage output from a solar cell is affected by the distance away from…
- Essay length: 3350 words
- Submitted: 01/02/2005
- Reviewed by: dragonkeeper13 14/04/2012
Although the candidate discusses all of the electromagnetic waves, the essay just focuses on the main body of information and there is no introduction. Having an introduction is crucial, it…
- Essay length: 1860 words
- Submitted: 13/01/2005
- Reviewed by: PicturePerfect 03/03/2012
The writer clearly targets the aim of the investigation, and consistently refers back to it and how the experiment is accomplishing it. The student gives a strong hypothesis backed up…
- Essay length: 1225 words
- Submitted: 13/01/2005
- Reviewed by: hassi94 19/03/2012
The writer has set out their objectives clearly and as a result, been able to produce a clear report. It would have been good for the writer to explain why…
- Essay length: 930 words
- Submitted: 13/01/2005
- Reviewed by: cpdavis 08/04/2012
The writer attempted this question to an okay standard. It was good that the writer used their initiative and decided to do background work in addition to a preliminary investigation.…
- Essay length: 1518 words
- Submitted: 20/10/2004
- Reviewed by: cpdavis 28/02/2012
Unfortunately the candidate has not written an introduction, they simply start off with the main information for the essay, which can be confusing when you first look at it. An…
- Essay length: 1498 words
- Submitted: 07/10/2004
- Reviewed by: pictureperfect 24/07/2012
- 1 When a source of waves is moving relative to an observer (either towards or away) the received waves have a different wavelength to the wavelength transmitted. This is known as the Doppler Effect and we can use it to calculate the speed of a galaxy relative to Earth.
- 2 Almost all galaxies show redshift, meaning that the wavelength received on Earth is longer than it was when transmitted. It’s called redshift because the wavelength received has moved towards tor even beyond the red end of the spectrum . Redshift implies that the galaxy is moving away from Earth.
- 3 Blueshift can be observed from ‘nearby’ stars and galaxies.
- 1 Using redshift data from a number of galaxies, Hubble plotted a graph of recession velocity, v, against distance to the galaxy, d. This graph continues to be updated and it shows that v = Hod which is known as Hubble’s law. This means that the speed of recession is directly proportional to the distance to the galaxy.
- 2 Ho is the Hubble constant and it has a value of about 70 km s-1 Mpc-1, which is equivalent to 2.3x10-18 s-1. 1/Ho= 4.4 x1017 s = 1.4 x 1010 years! This is the age of the universe, about 14 billion years.
- 3 We can also find an estimate for the size of the (visible) universe, assuming that the maximum expansion speed is the speed of light. Using Hubble law, c = Hod so d = c/Ho = 14 billion light years.
- 4 The uncertainty over the value of The Hubble constant is becoming smaller as measurements of distance to galaxies improve
- 5 Since redshift is seen in every direction, the conclusion is that the universe is expanding.
Fate of the universe
- 1 The fate of the universe is closely linked to CRITICAL DENSITY. This is a theoretical density that would have enough mass in the universe to keep the expansion of space slowing down forever. The critical density is given by o= 3H2/8 . The universe would be FLAT. An accurate value for H is important, if we want an accurate value for the critical density. Note: H2 means that the percentage uncertainty in H has to be doubled.
- 2 If the actual density is greater than the critical density, then the universe will stop expanding at some point and then collapse. The universe is then CLOSED. This outcome is known as the Big Crunch.
- 3 If the actual density is less than the critical density, there is not enough mass to stop the expansion and the universe will continue to expand forever. The universe is OPEN.
- 4 Determining the actual density is difficult because there seems to be dark matter which we cannot yet detect directly but which can be inferred by the gravitational effects it has. e.g the rotation of galaxies is not consistent with observable mass but with increased mass that may be explained by the presence of dark matter.
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