PROPAGATION OF ENERGY

1. UNIT-3
Propagation of energy
LP1: Transfer of energy-material medium:
 Transverse wave
 Longitudinal wave
 standing wave
 Interference
 Doppler effect

6. Transverse waves
In transverse waves, each particle oscillates perpendicular to
the direction of propagation of the wave. There is no
horizontal movement.
Transverse waves can be modelled by moving one end of a
Slinky up and down. Each coil represents a particle.
source moves
up and down
direction of wave
propagation
coils vibrate
up and down

18. The Principle of Superposition

19. Terminology
• Phase Difference: The fractional part of a period which represents
the offset in peak positions of waves.
• Coherence: The existence of a correlation between the phases of two
or more waves such that interference effects can be observed.
• Interference: The variation with distance or time of the amplitude of
a wave which results from the superposition of two or more waves.

22. Constructive Interference
• The superposition of two waves is called interference.
• Constructive interference occurs when both waves are
positive and the total displacement of the medium is larger
than it would be for either wave separately.

23. Destructive Interference
• Destructive interference is when the displacement of the
medium where the waves overlap is less than it would be
due to either of the waves separately.
• During destructive interference, the energy of the wave is
in the form of kinetic energy of the medium.

24. Standing Waves
• Waves that are “trapped” and cannot travel in either direction are
called standing waves.
• Individual points on a string oscillate up and down, but the wave
itself does not travel.
• It is called a standing wave because the crests and troughs “stand in
place” as it oscillates.

25. Superposition Creates a Standing Wave
• As two sinusoidal waves of equal wavelength and amplitude travel in
opposite directions along a string, superposition will occur when the
waves interact.

29. Doppler Effect
• “Along the line of sight” means the Doppler Effect happens only
if the object which is emitting light is moving towards you or
away from you.
• An object moving “side to side” or perpendicular, relative to your line
of sight, will not experience a Doppler Effect.

30. Doppler Effect
• When something which is giving off light moves
towards or away from you, the wavelength of the
emitted light is changed or shifted
V=0

31. Doppler Effect
• When the source of light is moving away from the observer the
wavelength of the emitted light will appear to increase. We
call this a “redshift”.

32. Doppler Effect
• When the source of light is moving towards the observer the
wavelength of the emitted light will appear to decrease. We call
this a “blueshift”.

33. Real Life Examples of Doppler Effect
•Doppler Radar (for weather)
•Airplane radar system
•Submarine radar system
Ok, anything with radar
•Radar gun, used by Law Enforcements Officers…

34. Doppler Shifts
• Redshift (to longer wavelengths): The source is moving away from the
observer
• Blueshift (to shorter wavelengths): The source is moving towards the
observer
Dl = wavelength shift
lo = wavelength if source is not moving
v = velocity of source
c = speed of light
c
v
0

l
l
D