Wave Properties

We will bginlooking at Waves by observing pulses on a rope We will bginlooking at Waves by observing pulses on a rope. The crest caused by the upward displacement travels away from the hand along the rope. This is a traveling wave. From this action, we can see that a wave is a disturbance that transfers energy from one point to another without imparting linear motion to the medium through which it propagates. (The particles of rope don’t move across the room, just the energy does)

Harmonic waves are produced by the simple harmonic motion (up and down) of one end of a string, which will resemble a sinusoidal wave, like a sin function. The top of the wave is called a crest while the bottom is the trough v = fλ: λ is wavelength f is frequency in Hz 1/f is period

Types of Waves There are two types of waves: Transverse – like waves on a string. Longitudinal – sound waves

Transverse Waves The energy transmitted by a wave is dependent upon amplitude, frequency, and mass of the particles in the medium. Think about putting waves through a rope, or through a piece of stretched thread. The rope will require more energy to move, but much more energy will be transferred than by a piece of thread, which has little mass.

Just as a pendulum is brought to rest eventually by friction bleeding off energy, friction between particles in the medium will bleed energy from the wave system. This energy loss can be seen in the reduction of amplitude as the wave travels away from the source. This reduction in amplitude is called damping, and may be very small over small distances.

Wave Interactions Waves can encounter basically two things, other waves and other mediums. The boundary between the wave medium and the other medium is called the interface. There are five properties that are common to all waves which can help us to determine if observed phenomenon involves a wave.

Wave Properties Rectilinear propagation – the direction of movement, propagation, of the wave front will be perpendicular to the wave front.

Reflection- when a wave rebounds off a barrier or new medium Reflection- when a wave rebounds off a barrier or new medium. The Θ of incidence = the Θ of reflection.

Θi = Θr If the boundary allows the unrestricted displacement of the medium, the wave will be reflected in phase. If the boundary restricts the displacement of the medium, the wave will reflect out of phase. If impedance is higher in the new medium, most of the energy will be reflected, and if impedance is lower, most of the energy will be absorbed.

Refraction The bending of the path of a wave as it enters obliquely (at an angle) into a medium with a different ability to conduct waves. This ability to conduct waves is called impedance. If the impedance is higher in the new medium, the wave will move more slowly, and will bend toward the Normal of the boundary. If impedance is lower, the opposite will occur. If impedance’s match, all energy will be transmitted into new medium, no refraction.

Shallow water has greater impedance, and the wave slows down as it enters shallow water, bending toward the Normal. When moving to deeper water, the wave speeds up and bends away from the normal.

Diffraction When waves encounter the edges of barriers, they will diffract, or spread around these edges. When the wavelength is much smaller than the opening in the barrier, little or no diffraction will occur.

Interference If two waves travel in the same medium, the action of each wave on a particle is independent of the other wave; therefore, the displacement of a particle will be the resultant of both wave actions. This is known as the superposition principle. Whenever two waves encounter each other, there will be interference.

Constructive interference will occur whenever the resultant displacement is greater than either individual wave; destructive interference occurs when the resultant displacement is less than either individual wave. When waves of equal wavelength and amplitude superpose in exactly opposite directions, a standing wave results. The stringed instrument is the best example of a standing wave.