seriously, can u get off ur
lazy ass and d/l syllabus summaries and read them.
eg. look wat i found
Outline the features of the aether model for the transmission of light
James Clerk Maxwell’s theory of electromagnetism proposed that light was an electromagnetic wave, and that it had a constant speed, c (3 x 108 ms-1), irrespective of the frame of reference of an observer. 19th Century physics only knew about waves that needed a medium to travel in, therefore light was assumed to travel through a medium too, named aether, and that the reason why light’s speed was constant was because it is measured with respect to the aether. Properties
of the aether included:
- it was transparent
- it flowed easy
- it does not offer resistance to masses
- it was stiff, so that light, which had a great speed, could travel through it
- it was elastic, to support and propagate light waves
Many of these characteristics were conflicting, but without aether, no other explanation could be
thought of. Therefore aether must have existed, being an absolute frame of reference (at rest).
Describe and evaluate the Michelson-Morley attempt to measure the relative velocity of the Earth through the aether
If aether existed, then the Earth should be moving through it, and a flow of aether should be experienced called aether wind. This is similar to the way wind is ‘created’ when a car is moving fast on a windless day. Sticking your hand out, you will be able to feel wind. Because of the properties of aether, extremely sensitive apparatus were needed to measure the relative velocity of the Earth through the aether. Michelson and Morley tried to measure the relative velocity of the Earth through the aether, by measuring the difference in the speeds of light beams when rotating the apparatus, which changed the direction of the light beam relative to the aether. It would have been impossible to measure the time difference between light, because it is so small, so they used the effect of interference of light. The apparatus involved a light ray travelling to a half-silvered mirror, which would split the beam into two directions, one into the aether, and the other against it. These two beams get reflected back by two mirrors and the two recombine at the interferometer. From here, an interference pattern is produced, appearing as a series of light bands in an eyepiece. If aether wind existed, when the apparatus was rotated, the eyepiece should see a shift in the light bands, and the relative velocity of the Earth through the aether could be measured. However, no shift was observed ever, no matter when and where the apparatus was tested, and no evidence for aether was found, famously called the ‘null’ result. No motion of the Earth relative to the aether was detectable.
Discuss the role of the Michelson-Morley experiments in making determinations aboutcompeting theories
The Michelson-Morley experiment detected no aether was present, and the null-result was a great mystery of physics. Many people tried to explain and keep the aether model alive by adapting the theory. One suggestion was that the Earth dragged the aether along with it, but this was shown to be incorrect. G.F Fitzgerald and H.A Lorentz both, independently, suggested that the length of the arms of the apparatus contract in the direction of the motion through the aether. As the contracted, the time changes cancel out, explaining why no shift was observed. At the time, no evidence supported of refuted this theory, but in 1979 it was shown that the length doesn’t contract. But long before this, Einstein’s special theory of relativity replaced the Lorentz- Fitzgerald theory. Although Einstein did not develop the theory specifically to answer the null result, it did succeed in explaining that the aether did not exist.
Thnx to
acmilan
