The Sagnac Effect


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Course Presentation trying to explain the sagnac effect

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The Sagnac Effect

  1. 1. The Sagnacs Effect Presentation Disclaimer: Due to the vastness of the topics covered, only the important themes are explained as understood (in the short interval.)
  2. 2. Overview • Relativity • Newtonian Relativity • Einstein's Relativity • Ritz Theory of Emission • Relativity vs. Emission Theory • The Sagnac’s Effect • Ring Laser Gyros • Summary
  3. 3. Relativity The fact that we cannot detect absolute motion is known as Relativity.
  4. 4. Relativity Video
  5. 5. Newtonian Relativity • Also known as classical relativity • Defined in terms of reference frame. • A reference frame in which Newton’s Laws hold is called an inertial frame • Postulates: 1. There exists an absolute space ( Newton Laws true) 2. All inertial frames share a universal time. • Time runs at the same rate in all frames (Galilean Transformation)
  6. 6. Newtonian Relativity
  7. 7. Newtonian Relativity
  8. 8. Newtonian Relativity 3 inertial frames: 1. Carrier-Earth (land underneath) 2. Car-Carrier 3. Car-Base CONCLUSION: Nothing (in terms motion-speed) is constant, every thing is relative to some other inertial frame of reference
  9. 9. Ritz Theory of Emission • A competing theory for the theory of relativity. • It obeys the central principal of relativity : No fixed frame of reference. • But claims: what if the light travels at a speed X with reference to the source? • Hence it tries to combine the laws governing electrodynamics and mechanics.
  10. 10. Einstein's Relativity • It is a theory of the structure of spacetime. • It is based on two postulates: 1. Laws of physics remain the same for all observers (who are in uniform motion relative to each other) 2. Speed of light is independent of the speed of any other object, even its source. • Postulate two contradicts Ritz Emission theory. • Important consequences include Relativity of simultaneity, Time Dilation, Energy Equivalence.
  11. 11. Einstein's Relativity vs. Newton • There is no universal time • Every inertial frame has its own independent time. • Speed of light binds all frames of reference.
  12. 12. Relativity vs. Emission Theory Emission theory was not able to explain the behavior of stars moving across our field of vision.
  13. 13. The Sagnac’s Effect • A phenomenon observed during interference of waves when the source is rotated. • A beam of light is split in two. • Beams travel in opposite direction • When apparatus is stationary both beam have an equal distance to cover. • Due to rotation of the apparatus both beams face unequal distances. • Interference occurs.
  14. 14. The Sagnac’s Effect Video1 Video 2 Sagnac’s effect dismisses emission theory and strengthens the case for special relativity.
  15. 15. Sagnac Effect (Uses): RLG • The apparatus can be made to measures its own angular velocity with respect to the local inertial frame. • Hence it is highly effective for use in inertial guidance systems. • It is the basis for any Ring Laser Gyro
  16. 16. Ring Laser Gyro
  17. 17. Patterns COUNT No. OF MOVING PARTS
  18. 18. Problem • RLGs suffer from “lock-ins" at very slow rotation rates. • Is solved by automatic rotation of apparatus (Dithering)
  19. 19. Summary • Newtonian Relativity: Universal time and Absolute space • Einstein Relativity: Independent time and inertial frames, concept of spacetime fabric. • Ritz Emission theory: Light moving with a speed RELATIVE to its source (rejected) • Sagnac’s effect: Interference of two beams of light due to rotation. • RLG: Working and Problem (solved)
  20. 20. THANK YOU
  21. 21. ? ?? Questions