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Types of Waves
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3

Properties of Waves

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3.1

General wave properties

 
Core-1 Describe what is meant by wave motion as illustrated by vibration in ropes, springs, and by experiments using water waves.  
Core-2  Use the term wave front  
Core-3  give the meaning of speed, frequency, wavelength and amplitude   
Core-4  Distinguish between transverse waves and longitudinal waves and give suitable examples.  
Core-5  Describe the use of water waves to show (i) Reflection at a plane surface (ii) refraction at a plane surface.  
Sup-1  give a meaning to the term wave front  
Sup-2  recall and use the equation  v=fL  
Sup-3  interpret reflection, refraction, differeaction  

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.
    You need a Java-enabled browser.
  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.
    Point on a wave
  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 wavelengthwavelength 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: Velocity
  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 10
    6 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/wavelength=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.

    Transfering waves

  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.
    Constructive interference
  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.
    Destructive interference
  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.

    incident/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.
    Denser mediumRarer medium
  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

Test yourself
1. The velocity of a wave is 420 m/s. If the frequency of the wave is 85 Hz, what is its wavelength?

m

2. If a wave with a wavelength of 5.0 m has a 3.0 * 10-3 s period,

a. what is its frequency?

Hz

b. what is its velocity?

m/s

3. What is the period of a sound wave that has a frequency of 163 Hz?

(e.g. "2.4 * 10E-3") s

4. If a wave with a frequency of 342 Hz and a velocity of 234 m/s is produced...

a. what is its wavelength?

m

b. how far is the wave after 3.6 s?

m

5. A traveling wave is produced on a rope. The wave travels until it hits a wall and it is reflected. If the speed of the wave is 1.8 m/s and it takes 10.4 s to reach the origin again, ...

a. how long is this rope?

m

b. what is the wavelength of the wave if it has a period of 2.1 s?

m

 

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