2. Introduction to Waves

3. Rhythmic disturbances that carry energy without carrying matter What are Waves?

4.  The source of all waves is something that vibrates.  A wave is a means of transferring energy from one place to another.  When energy is transferred by a wave from a vibrating source to a distant receiver, no matter is transferred between the two points Most information gets to us in some form of wave. Sound is energy that travels to our ears in the form of a wave. Light is energy that comes to our eyes in the form of a different kind of wave (an electromagnetic wave). The signals that reach our radio and television sets also travel in the form of electromagnetic waves.

5. Drop a stone in a quiet pond and you’ll produce a wave that moves out from the center in an expanding circle. It is the disturbance that moves, not the water.

6. Types of Waves Waves are of three main types: Mechanical waves: Waves that need matter (medium) to transfer energy: A medium is the substance through which a wave can travel. Ex. Air; water; particles; strings; solids; liquids; gases Because of the elastic properties of the medium, the disturbance travels through the medium.

7. On a microscopic level, the forces between atoms are responsible for the propagation of mechanical waves. Each atom exerts a force on the atoms that surround it and through this force, the motion of the atom is transmitted to its neighbor. However the particle of the medium do not experience any net displacement in the direction of wave. As the wave passes, the particle simply move back and forth through small distance about their equilibrium positions. Common examples include sound waves, ocean waves, ripples in water,, and seismic waves.

8. Electromagnetic waves. Waves that do not need matter (or medium) to transfer energy For example light waves from stars travel through the vacuum of space to reach us. These waves do not need a medium to exist, but they can go through matter (medium), such as air, water, and glass. All electromagnetic waves travel through a vacuum at the same speed c = 299, 792, 458 m/s. Common examples include visible and ultraviolet light, radio and television waves, microwaves, lasers, x rays, and radar waves.

9. Matter waves. These waves are associated with electrons, protons, and other fundamental particles, and even atoms and molecules. Because we commonly think of these particles as constituting matter, such waves are called matter waves.

10. Transverse waves A transverse wave is a one in which the direction of vibration (or motion of the particles) is perpendicular to the direction of propagation of the wave. For example, when a string under tension is set oscillating back and forth at one end, a transverse wave travels along the string; The disturbance moves along the string but the string particles vibrate at right angles to the direction of propagation of the disturbance.

11. Longitudinal Waves: A longitudinal wave is one in which the direction of motion of the oscillating particles is parallel to the direction of propagation of the wave. For example, a sound wave is set up in an air filled pipe by moving a piston back and forth. Because the oscillations of an element of the air (represented by the dot) are parallel to the direction in which the wave travels, the wave is a longitudinal wave.

12. Examples of Compressional Wave (longitudinal)  Sound waves in a solid, liquid or gas.  Compression waves on a spring.  Seismic waves. A slinky is a good illustration of how a compressional wave moves

13. The differences between the two can be seen Elements move perpendicular to wave motion. Elements move parallel to wave motion

14. Complex waves: Some waves are neither purely longitudinal nor purely transverse. For example in waves on the surface of water, the particles of water move both up and down and back and forth, tracing out elliptical paths as the water move by.

15. Quick Quiz (i) In a long line of people waiting to buy tickets, the first person leaves and a pulse of motion occurs as people step forward to fill the gap. As each person steps forward, the gap moves through the line. Is the propagation of this gap (a) transverse or (b) longitudinal? (ii) Consider the “wave” at a baseball game: people stand up and raise their arms as the wave arrives at their location, and the resultant pulse moves around the stadium. Is this wave (a) transverse or (b) longitudinal? (i), (b). It is longitudinal because the disturbance (the shift of position of the people) is parallel to the direction in which the wave travels. (ii), (a). It is transverse because the people stand up and sit down (vertical motion), whereas the wave moves either to the left or to the right.

16. Waves can also be classified as propagating in one, two and three dimensions. Waves moving along the string or spring are one dimensional. Surface waves or ripples on water caused by dropping a pebble into quite pond are two dimensional. Sound waves and light waves travelling radially outward from a small source are three dimensional. Number of dimensions:

17. Periodicity: Waves may be classified further according to how the particles of the medium move in time. For example a single wave pulse through the string can be produced by applying a s single side wise movement at its end. Each particle remains at rest until the pulse reaches it, then it moves during a short time and then it again remains at rest.

18. If we continue to move the end of the string back and forth periodically, a periodic train of waves can be produced in which each particle of the string has periodic motion. The simplest case of periodic wave is harmonic wave in which each particle undergoes simple harmonic motion

19. Aperiodic wave Periodic wave

20. Shape of wave front: Imagine a stone dropped in a still lake. Circular ripples spread outward from the point where the stone entered the water. The direction of motion of the wave is at right angles to the wave front. Along a given circular ripple, all points are in the same state of motion. Those points define a surface called a wave front. A line normal to the wave fronts, indicating the direction of motion of wave, is called a ray.

21. A wave front is a surface passing through points of a wave that have the same phase and amplitude The rays, corresponding to the direction of the wave motion, are perpendicular to the wave fronts

22. Wave fronts can have many shapes. Circular wave: A point source at the surface of wave produces two- dimensional waves with circular wavefront and rays that radiate outward from the source of disturbance. Plane wave: A long stick dropped horizontally into the water would produce disturbances that travel as straight lines, in which the rays are parallel lines.

23. The three dimensional analogy, in which the disturbances travel in a single direction, is plane wave. At a given instant, conditions are the same everywhere on any plane perpendicular to the direction of propagation. The wavefronts are planes, and the rays are parallel straight lines.

24. Spherical wave: The three dimensional analogy of circular waves is spherical waves. Here the disturbance is propagated outward in all directions from a point source of waves. The wavefronts are spherical, and the rays are radial lines leaving the point source in all directions

25. Periodic Wave Properties (Vocabulary) Frequency (f) is the number of oscillations per second at a fixed point in space Period (T) is the inverse of frequency, is the time it takes for one wavelength to pass a fixed point Ray: Direction of wave motion