Waves and Sound A. Definition - Fort Bend ISD

I. Wave Characteristics

Waves and Sound

A. Definition

A wave is a transfer of ENERGY from one point to another without the transfer of material between the points

WAVES "MOVE" ENERGY, NOT MATTER

Amplitude: the height of the wave, measured in meters. Wavelength (): the distance between adjacent crests, measured in meters. Period: the time it takes for one complete wave to pass a given point, measured in seconds. Frequency: the number of complete waves that pass a point in one second, measured in inverse seconds, or Hertz (Hz). Speed: the horizontal speed of a point on a wave as it propagates, measured in meters / second.

crest

trough

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B. Some basic equations relating wave properties

= 1 T

T=1 f

v =

frequency (Greek letter )

period speed

Be careful interpreting this equation. It would seem that changing wavelength would change wave speed but it does not.

This has to do with how wavelength and frequency are related. Doubling the wavelength does not double the speed because it has the effect of reducing the the frequency by half. SPEED REMAINS THE SAME.

WAVE SPEED DEPENDS ON THE MEDIA IN WHICH THE WAVE TRAVELS.

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II. TYPES

A. MECHANICAL WAVES-move through a media (solid, liquid, or gas) longitudinal-medium displacement is in the same direction the wave propagates transverse- medium displacement is perpendicular to the direction the wave propagates

Water wave are capable of combining both types of motion. Therefore, an object suspended in the wave moves in a circle as the wave propagates.

Animations of these motions can be found here: wave motion animations B. STANDING WAVES-waves whose movement is constrained to a constant position.

Plucking the string of an instrument creates a standing wave. See sounds lesson. Holding a rope at both ends and shaking it creates standing waves. The point(s) on a standing wave that remain stationary are called nodes. The point(s) of highest amplitude are called antinodes, found halfway between nodes.

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C. ELECTROMAGNETIC WAVES-transverse waves that DO NOT require a medium through which to travel.

They have an electric field and a magnetic field that propagate in the same direction but the fields are perpendicular to each other. They can be POLARIZED. This means they can be filtered so that only one direction of the electric field passes a polarizing filter.

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III. Adding Waves-Interference The nodes and antinodes of waves that are IN-PHASE "line up" When added, a wave with a larger amplitude results The nodes and antinodes of waves that are out of PHASE are "off set" When added, they cancel

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