IB Study Guide
Evidence:
Muons are produced 10 km above the surface of the earth when cosmic rays from the sun interact with the atmosphere giving them speeds of 0.99c. They have a half life of 2.2 * 10-6 seconds which means that they should only be able to travel about 1 km before decaying and we should not be able to detect any muons at the surface of the earth. But we do.
gamma factor = 7.1
Conclusions:
As the muons is travelling close to the speed of light, special theory of relativity applies. This means that time is dilated; to an observer on earth, the muon's half life will appear to be 7.1 * 2.2 * 10-6 seconds. Time dilates. Also, the distance that they have to travel appears to be 10/7.1 km = 1.4 km. The distance contracts. As the time dilates and the distance contracts, the muons appear to survive long enough to reach the surface of the earth, which supports the special theory of relativity.
IB Question:
Michelson Morley Experiment:
The aim of this experiment was to test for the presence of ether (which is what scientists thought was the medium through which light travels).
So for sound, if the wind was moving in the direction of the sound wave, sound would travel faster and if the wind was moving in the opposite direction, then sound should travel slower. They thought the same was true of light and ether. The animation below shows the predicted results of the Michelson Morley experiment:
Method:
In the centre is a half mirror that splits the incident beam of light into two (one reflected and one passed through) that have equal intensities that hit mirrors, converge back at the half mirror and strike the detector.
Depending on the direction of the ether, one beam was thought to arrive faster than the other.
The experiment was repeated by rotating the apparatus and measuring differences in speed of the return beams.
Interference patterns of the two light beams were used to detect differences in their return time)
But this did not happen, and they both arrived at different times. This proved firstly that ether doesn't exist and that the speed of light is constant.
Pion Decay experiment:
A pion was accelerated close to the speed of light. When it decayed it produced two gamma-ray photons. The speed of these photons was not the sum of the speed of the pion and the photon as Galilean transformations would suggest but was the speed of light. This once again proved the second postulate of the special theory of relativity that the speed of light is constant in all inertial frame's of reference.
No comments:
Post a Comment