• Ripple Tank – a shallow tank used to study waves.
  • A crest in the wave causes light to bend inwards (converge) when illuminated from above. This produces a brighter region on the screen. The opposite happens if the illumination is from below.
  • A trough causes light to bend outwards (diverge) when illuminated from above. This produces a darker region on the screen. Again, the opposite happens if the illumination is from below.
  • The resulting dark and bright regions on the screen allow one to observe the overall wave pattern.
• Point Sources – produce circular waves in a two dimensional space (like water in a ripple tank).
• Linear Source – produces a linear straight wave in a two dimensional space (a dowel in a ripple tank).
• For the ripple tank, velocity decreases as the depth decreases
• For water waves, the universal wave equation still applies.
  • Velocity depends upon the medium characteristics (e.g. Depth)
    • Is a constant for a given medium.
  • Frequency depends upon the source.
  • Wavelength depends upon the source and the medium.
    • As Frequency increases wavelength decreases and vice versa.
    • As velocity increases wavelength increases and vice versa.
• Wave front – a continuous crest or trough in a two-dimensional or three-dimensional space.
• Wave Ray – An arrow drawn perpendicular to the wave front, which shows the direction of motion of the wave front(s).

• Waves reflect off of barriers
• Normal – is a straight line drawn perpendicular to the barrier or boundary between media.
• Incident Ray – the wave ray showing the direction of motion of the wave approaching the barrier or boundary between media.
• Reflected Ray – the wave ray showing the direction of motion of the wave moving away from the barrier.
• Angle of incidence – the angle between the incident ray and the normal.
• Angle of reflection – the angle between the reflected ray and the normal.
• Refracted ray – the wave ray showing the direction of motion of the wave moving away from the boundary between two media.
  • The wave must move from one medium to another before we can use this term.
• Angle of refraction – the angle between the refracted ray and the normal.

• The Laws of Reflection –

1. The angle of incidence equals the angle of reflection.

2. The incident ray, reflected ray and the normal are all on the same plane.

• This law applied to waves in three-dimensional space like light or sound.
• By applying the laws of reflection we can show

1. circular waves reflected off of a straight barrier remain circular.

2. straight waves reflected off of a straight barrier remain straight

3. straight waves reflected off of a parabolic barrier become circular.

4. Circular waves produced at the focal point of a parabolic reflector are

changed to straight waves.

• Focal Point – the point through which all the reflected wave rays pass, after parallel incident rays reflect off of parabolic reflectors.
• In all wave reflections, there are no changes in velocity, frequency, or wavelength of the wave.

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November 6, 2013