Doppler Effect

1
Lecture 3

• Doppler Effect
• - Doppler effect in sound Increase in pitch of
  a sound when its source is approaching or
  decrease when the source moves away.
• Doppler effect in sound varies depending on
  whether the source or the observer or both are
  moving
• Sound waves occur only in a material medium such
  as air or water and the medium is itself a frame
  of ref with respect to which motion of source and
  observer is measured.
• What about LIGHT? no medium inolved.
• - Longitudinal Doppler Effect
• - Transverse Doppler Effect

2
Relativistic Longitudinal Doppler Effect - Time
Dilation Classical Doppler Effect
Source moves towards you compress the waves
increase in freq
Source moving towards observer f frequency
measured by observer f frequency measured in
source frame fgtf for approaching source fltf for
source moving away
3
Experimental study of rate of a Moving Atomic
Clock JOSA, Vol 28, 1938 H.E. Ives and G.R.
Stillwell , Bell Labs
v

• F is a positive electrode
• A is a grounded electrode with holes drilled in
  it
• B is a negative electrode with holes drilled in
  it
• C is a mirror, the reflective side of which
  points to the right

glass tube which created ionized hydrogen atoms
by passing a high-voltage spark through hydrogen
gas
4
Transverse Doppler Effect
Observer moving perpendicular to the source
Time dilation problem.
Place a source of gamma rays on the axis of a
centrifuge, and an absorber out on the edge W.
Kundig, PRL, Measurement of Transverse Doppler
Effect in Accelerated System, 1963
5
Twin Paradox
6
Pole and Barn Paradox
Frame of Farmer Barn
Frame of Runner
7
Headlight effect
8
Superluminal Speeds?
9
Stenner, Gauthier, and Neifeld, Nature 425, 665
(2003)
10
Backwards in time?