Properties of Waves

1. What are the three types of waves?
   1. Mechanical waves require a material medium to travel (air, water, ropes). These waves are divided into three different types: transverse, Longitudinal, and surface waves. 
   2. Electromagnetic waves do not require a medium to travel (light, radio).
   3. Matter waves are produced by electrons and particles.
   4.  
2. What is meant by transverse waves?
   transverse waves cause the medium to move perpendicular to the direction of the wave.
   
3. What is meant by Longitudinal waves ?
   Longitudinal waves cause the medium to move parallel to the direction of the wave.
   
4. What is meant by Surface waves?
   Surface waves are both transverse waves and longitudinal waves mixed in one medium.
   
5. What is a pulse?
   Pulse is a single vibration. By moving a rope once, a single vibration is produced. Click on the image to produce a pulse.
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6. What is a wave?
   A wave is a series of pulses.  By moving a rope regularly up and down, a traveling or periodic wave is produced.
   
7. What is meant by "wave period"?
   Any point on a transverse wave moves up and down in a repeating pattern.
   The shortest time that a point takes to return to the initial position (one vibration) is called period, T. In this example, every vibration is marked with a short pause.
   
   
8. What is meant by "wave frequency"?
   The number of vibrations per second is called frequency and is measured in hertz (Hz). Here's the equation for frequency:
   f = 1 / T
   
9. What is meant by "wave amplitude"?
   The amplitude of a wave is the distance from a crest to where the wave is at equilibrium. The amplitude is used to measure the energy transferred by the wave. The bigger the distance, the greater the energy transferred.

   

10. What is meant by "wave length"?
    The wavelength is the distance between two crests or two troughs.

    

11. What is meant by "wave phase"?
    Phase is used to describe the starting points of two waves.  If their crests start at the same time they are called in phase if not they are called out of phase.  If the difference between the two crests is 180 degrees they are called completely out of phase. 
    
12. What is meant by "wave front"?
    Wave front is a line or a surface perpendicular to the wave direction and on which all disturbances at every point have the same phase.
    
    
13. What is meant by ray?
    A ray is a line which represents the direction of travel of a wave and it is always at right angle to the wave front.
14. How the speed of a wave is related to its length and frequency?
    By knowing the frequency of a wave and its wavelength, we can find its velocity. Here is the equation for the velocity of a wave:
15. Does the velocity of a wave depend on frequency or wave length of the wave?
    No it does not. The velocity of a wave is only affected by the properties of the medium. It is not possible to increase the speed of a wave by increasing its wavelength. By doing this, the number of vibrations per second decreases and therefore the velocity remains the same.
16. A radio wave has a frequency of 93.9 MHz (93.9 * 10⁶ Hz). What is its period?
    f = 93.9 * 10⁶ Hz
    f = 1 / T
    T = 1 / f
    
    T = 1 / 93.9 x 10⁶ Hz
    T = 1.06 x 10^-8 s
17. If the velocity of a radio wave is 300 000 000 m/s (light speed) and its wavelength is 3.0 m, what is the frequency of the wave?
    f=c/=300 000 000/3.0=100,000,000 Hz
18. What happens to a wave when it moves form one medium to another medium?
    Once a wave (incident wave) has reached the end of a medium, part of the energy is transferred to the medium that is immediately next to it (transmitted wave) and part is reflected backward (reflected wave).

    The energy transferred depends on the difference between the mediums. If there is a significant difference, almost all the energy will be reflected. If the mediums are similar, most of the energy will be transferred. However, the reflected waves will be inverted if the medium that comes next is more dense or it won't be inverted if the medium is less dense.

    

19. What is meant by Collision of waves?
    When two waves traveling in opposite directions through the same medium collide, the amplitude of the resulting wave will be the sum of the two initial waves. This is called interference and there are of two types:
20. What is meant by a constructive interference?
    Constructive interference is when the amplitudes of the initial waves are in the same direction. The resulting wave will be larger than the original waves. The highest point of a constructive interference is called an antinode.
    
21. What is meant by Destructive interference?
    Destructive interference is when the amplitudes of the initial waves are opposite. The amplitude of the resulting wave will be zero. The point in the middle of a destructive interference is called a node and it never moves.
    
22. What is meant by reflection of waves?
    When a wave hits a barrier, it will be reflected depending on the direction of the barrier (normal). The angle between the incident wave and the normal is the same as the angle between the normal and the reflected wave.

    
    

23. What is meant by refraction?
    When a wave enters a different medium (more shallow region) at an angle, the direction of waves changes. This change is called refraction.
    
    
24. What is meant by diffraction?
    When a wave travels through a small hole in a barrier, it bends around the edges. This is called diffraction.
    
25. What happen to the following wave properties if it undergoes reflection, refraction and diffraction?

    Wave parameter	Reflection	Refraction	Diffraction
    speed	same	changes	same
    frequency	same	same	same
    wavelength	same	changes	same
    Amplitude	changes	changes	same
    Phase	changes	changes	same
    Direction	changes	changes	changes

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Created SEP 1, 2000
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Designed by: R. K. Abu-Msameh
Last modified: November 29, 2000