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Waves. Energy can be transported by transfer of matter. For example by a thrown object. Energy can also be transported by wave motion without the transfer of matter. For example by sound waves and electromagnetic waves. Waves.
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Waves • Energy can be transported by transfer of matter. For example by a thrown object. • Energy can also be transported by wave motion without the transfer of matter. For example by sound waves and electromagnetic waves.
Waves • Mechanical waves travel through matter. The matter is referred to as a “medium”. Examples are sound eaves, waves on a string, and waves on water. • Electromagnetic waves do not require a medium through which to travel. Examples are gamma rays, x-rays, ultraviolet light visible light etc.
Waves • A waveis a disturbance or oscillation that travels through matter or space, accompanied by a transfer of energy.
Waves • A transverse wave causes the medium particles to vibrate in the direction perpendicular to the motion of the wave.
Waves • A longitudinal wave causes the medium particles to vibrate in the direction parallel to the motion of the wave.
Waves • A pulse is a single disturbance travelling through a medium or space.
A crest is the point on a wave with the maximum value of upward displacement within a cycle.
A trough is the point on a wave with the minimum value of downward displacement within a cycle.
The amplitude is the value of the maximum or the minimum displacement from the average position
The wavelength (l) is the distance between corresponding points on consecutive waves.Unit: m
The frequency (f) is the number of waves that pass a given point per unit time.Unit: Hz=s-1
Waves A standing wave oscillates with time but appears to be fixed in its location
Figure 14-19Wave superposition occurs when two or more waves meet in the same medium. The principle of superposition states that at the point where two or more waves meet the displacement of the medium equals the sum of the displacements of the individual waves.
Figure 14-20The effect of two or more waves travelling through a medium is called interference. Constructive interference Destructive interference
Figure 14-20Nodes and antinodes • Nodes occur at points where two waves interact in such a way that the medium remains undisturbed. • Antinodes occur at points where two waves interact in such a way that maximum displacement of the medium occurs.
Figure 14-20Nodes and antinodes Node Antinode
Figure 14-20Nodes and antinodes • If one end of a string is attached to a vibrating object, and the other end is fixed, two wave trains are produced. One by the incident vibration, and one by reflection from the fixed end. The reflected wave train returns to the source and is reflected again. If the second reflection is in phase with the source, constructive and destructive interference will produce stationary antinodes and nodes. The string will appear to be vibrating in segments.
Figure 14-20Nodes and antinodes • This is called a standing wave an is an example of resonance.
Reflection of Waves • When a wave train strikes a barrier it is reflected. • The law of reflection states that the angle of incidence is equal to the angle of reflection. • The direction of the wave train’s travel is called a ray, and the angles are measured from the normal to the boundary.
Refraction of Waves • When a wave train moves from one medium to another, its velocity changes. • Since the waves in the new medium are produced by the waves in the old medium, their frequency remains the same. Since the velocity changes, but not the frequency, the wavelength must change.
Refraction of Waves • When parallel waves approach a boundary between media along the normal, their direction does not change. • When parallel waves approach a boundary between media at an angle to the normal, their direction is changed. This phenomenon is called refraction.
Refraction of Waves • When parallel waves approach a boundary between media along the normal, their direction does not change. • When parallel waves approach a boundary between media at an angle to the normal, their direction is changed. This phenomenon is called refraction.
Refraction of Waves Boundary
Refraction of Waves Boundary
Diffraction of Waves • Diffraction is the bending of waves around obstacles in their path.
Diffraction of Waves • An interference pattern can be created by placing a barrier with two openings in front of a wave train. • The openings must be smaller than the wavelength of the approaching wave train.
Diffraction of Waves • In regions where crests overlap with crests, and troughs overlap with troughs, constructive interference occurs, and antinodes lie along those lines. These lines are called antinodal lines. • In regions where crests overlap with troughs destructive interference occurs, and the medium is undisturbed. These lines are called nodal lines.
Diffraction of Waves • The pattern produced is called an interference pattern. • Different wavelengths produce similar interference patterns, but the nodal and antinodal lines are in different places. • Regardless of wavelength a central antinodal line always falls in the center of the pattern.
Standing waves on a string – In order for standing waves to form on a string, the length of the string L must be a multiple of one half the wavelength
