Air Column The Phase Of A Wave example essay topic

INTERNATIONAL BACCALAUREATE SUBSIDIARY LEVEL WAVES SUMMARY 4.1 Travelling wave characteristics A medium is a material through which a wave passes. When a wave passes, each part of the medium moves away from its normal position and then returns. This is called an oscillation. Oscillations within the medium are slight movements either side of the normal position.

The wave motion is the disturbance that passes through the medium. A wave pulse causes the medium to have one oscillation. A continuous travelling wave causes the medium to keep oscillating. Waves transfer energy without transporting matter because each part of the medium oscillates on the spot.

A transverse pulse causes the spring to move at right angles to the direction of motion of the pulse. A longitudinal pulse causes the spring to move parallel to the direction of motion of the pulse. The direction of propagation is at right angles to the wavefront. The displacement at a point is how much the medium has been displaced from its normal position.

Displacements are given + or - signs depending on the direction of the displacement. Amplitude is the largest distance from the normal position that the medium is displaced. The wavelength l of a wave is the distance from one point to the next corresponding point. The period T of a wave is the time in seconds that it takes one wavelength to pass by.

In this time the medium will complete one oscillation. The frequency f of the wave is the number of wavelengths that pass each second. Frequency and period are reciprocals. T = 1/f. The speed of a wave is equal to its frequency times its wavelength.

A displacement / position graph shows the displacement of the different sections of a medium. A displacement / time graph shows the displacement of one point of a medium as time elapses. The speed of the particles of a medium is a maximum when their displacement is zero. The speed of the particles of a medium is zero where the medium has maximum displacement. For a longitudinal wave, the medium has a high pressure called a compression where particles are closer than normal. For a longitudinal wave, the medium has a low pressure called a rarefaction where particles are further apart than normal.

The particles around a compression move in the same direction as the wave. The particles around a rarefaction move in the opposite direction to the wave. The particles near a compression and rarefaction have small displacements. The particles where the pressure is normal, have large displacements.

4.2 Wave Properties For a transverse wave, the phase of a wave is the side of the normal position that the displacement occurs. The speed of a pulse depends on the tension in the spring and the mass of the spring per metre. The greater the tension the faster the pulse. The greater the mass per metre the slower the pulse.

Transmitted pulses always have the same phase as the incident pulse. Transverse pulses reverse their phase when reflecting from a fixed end. Transverse pulses keep the same phase when reflecting from a free end. When a transverse pulse moves towards a heavier spring the partial reflection has the reverse phase. When a transverse pulse moves towards a lighter spring, the partial reflection has the same phase. Huygens principle - every point on a wavefront is a source of secondary circular waves.

When a wave meets a boundary the angle of incidence is the angle between the direction of propagation and the normal. When a wave reflects off a barrier the angle of incidence is equal to the angle of reflection. When a wave travels from deep water into shallow water, it slows down and refracts towards the normal. This is refraction. 2. When refraction occurs, the speed and wavelength change but the frequency remains constant.

When a wave travels from deep water into shallow water, sine of the angle of incidence divided by the sine of the angle of refraction is equal to the speed in the deep water divided by the speed in the shallow water. This is Snell's law. Diffraction is the change in the direction of a wave when it passes near an edge or through a gap. The greater the ratio of wavelength to obstacle or gap size, the greater the diffraction. Superposition: When two pulses over lap the total displacement equals the sum of the individual displacements. Constructive interference occurs when crests overlap crests and troughs overlap troughs.

Destructive interference occurs when a crest overlaps a trough. Doppler effect is the apparent change in frequency of waves emitted by a source when the source or the observer is moving. If the distance between the source and the observer is decreasing a higher frequency is detected. If the distance between the source and the observer is increasing a lower frequency is detected.

4.3 Standing waves Standing waves are the vibrations on the spot formed by waves moving through each other from opposite directions, with the same frequency and similar amplitude. Nodes are the places which always have zero displacement. Antipodes have displacements that fluctuate between maximum positive and negative values. The nodes in a standing wave pattern are separated by half the wavelength of the waves moving through each other.

A node exists at a fixed end and an antinode exists at a free end. In an air column, an antinode is at an open end and a node is at a closed end. In an air column the phase of a wave reverses when it partially reflects from an open end. In an air column the phase of a wave remains the same when it partially reflects from a closed open.

In an air column, the air has zero displacement at nodes. In an air column, the displacement of the air fluctuates between two extremes at the antipodes. In an air column the displacement of the air is small near nodes and large near antipodes. In an air column, air pressure fluctuates between two extremes at nodes. There is normal pressure at antipodes. Resonance occurs when a string / air column is stimulated by a vibration with the same frequency as one of its standing wave modes of vibration.

When resonance occurs, the amplitude of the standing wave is very large.