Phy Relativity Flashcards
(14 cards)
Explain Inertial Frame
It is basically a reference frame from which Newtons laws must be valid in that frame. Since we are measuring these observation from some sort of reference frame.
What is the Newtonian Principle of relativity or the Galilean invariance ?
This principle means that if Newton’s laws are valid in one reference frame, then it will be valid in system that moves with uniform velocity moving relative to the first frame.
Galilean Transformation
This transformation involves that newton idea of time being absolute came up with equations that would showcase this from one co-ordinate system to another .These equations are thus the galilean transformation. Review them and know that x’ = x-vt, y’=y, z’=z, t’=t
Ether
It is this idea in which we know that waves of all kind requires some medium to pass through except light which requires none and this medium is usually called the luminiferous ether or just ether.
What device did Michelson used to try to detect the ether ?
Interferometer.
Explain shortly about Michelson experiment.
Michelson and Morley built a Michelson interferometer, which essentially consists of a light source, a half-silvered glass plate, two mirrors, and a telescope. Eric Weisstein’s World of Astronomy The mirrors are placed at right angles to each other and at equal distance from the glass plate, which is obliquely oriented at an angle of 45° relative to the two mirrors. In the original device, the mirrors were mounted on a rigid base that rotates freely on a basin filled with liquid mercury in order to reduce friction.
Michelson and Morley were able to measure the speed of light by looking for interference fringes between the light which had passed through the two perpendicular arms of their apparatus. These would occur since the light would travel faster along an arm if oriented in the “same” direction as the ether was moving, and slower if oriented in the opposite direction. Since the two arms were perpendicular, the only way that light would travel at the same speed in both arms and therefore arrive simultaneous at the telescope would be if the instrument were motionless with respect to the ether. If not, the crests and troughs of the light waves in the two arms would arrive and interfere slightly out of synchronization, producing a diminution of intensity. (Of course, the same effect would be achieved if the arms of the interferometer were not of the same length, but these could be adjusted accurately by looking for the intensity peak as one arm was moved. Changing the orientation of the instrument should then show fringes.)
Although Michelson and Morley were expecting measuring different speeds of light in each direction, they found no discernible fringes indicating a different speed in any orientation or at any position of the Earth in its annual orbit around the Sun.
What are Einstein’s two postulate or what we called now “laws”
- Principle of relativity- The laws of physics are same in all inertial frames of reference and there are no preferred ones or no way to detect absolute motion.
- The constancy of the speed of light- observers measure the speed of light to be the same value in a vacuum for all inertial frames of reference.
How did the postulates revised definition for inertial reference frames ?
It did so by including all laws of physics instead of just Newton’s laws only.
What is the best way to synchronize clocks ?
This can be done by sending light signals to each observers in a specified location to see if they reach simultaneously.
The Lorentz Transformation
It is where we use Einstein’s two postulates to find a transformation between inertial reference frames that obey the postulates and have the same form. Read and review equation and how it corrects the Galilean transformation eqn’s
The implications of Lorentz Transformation
The linear transformation equations ensure that a single event in one system is described by a single event in another inertial system. However, space and time are not separate. In order to express the position of x in system K’, we must use both x’ and t’. We have also found that the Lorentz transformation does not allow a speed greater than c; the relativistic factor Gamma becomes imaginary in this case. We show later in this chapter that no object of nonzero mass can have a speed greater than c.
Consequences of Lorentz transformation
Time dilation and Length contraction.
What is proper time
The time difference between two events occurring at the same position in a system as measured by a clock at rest in the system
T_0= T2-T1
Time dilation
It is where the time interval is greater in a moving system rather than in a system at rest.
‘‘moving clocks run slow’’
The clock at rest will always give the smallest time interval between two events.
