Waves and Wave Motion

Waves and Wave Motion

1. Types of waves

   • Mechanical waves
     • A mechanical wave passes through a medium as vibrations are passed on from molecule to molecule
     • E.g water waves, waves on a rope, ultrasonic waves
   • Electromagnetic waves
     • An electromagnetic wave can pass through a vacuum as they do not need a medium to travel through. They travel at the speed of light (3x10^8)
     • E.g light waves, ultraviolet waves, x-ray

2. A transverse wave is a wave where the direction of vibration is perpendicular to the direction in which the wave travels

3. A longitudial wave is a wave where the direction of vibration is parallel to the direction in which the wave travels

4. The top of a wave is the crest and the bottom of a wave is the trough. The maximum distance of any particle from its undisturbed position is the amplitude (A). The distance travelled by one cycle in one second is called the velocity (c)

5. C = f λ

   • c - velocity
   • f - frequency
   • λ - wavelength

6. Wave phenomena

   • The bouncing of waves off of an obstacle in their path is called reflection of waves
   • The changong of direction of a wave when it enters a region where its speed changes is called refraction
   • The sideways spreading of waves into the region beyond a gap or around an obstacle is called diffraction
   • When waves from 2 sources meet, a new wave is produced. This is called interference of waves
   • Polarisation is when a wave travels in the same plane

7. Wave interferences

   • When waves from 2 sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves, the waves are said to undergo constructive interference
   • When waves from 2 sources meet and the amplitude of the resulting wave is less than the amplitude of each of the individual waves, the waves are undergoing destructive interference

8. 2 sources of periodic waves are said to be coherent if they are in phase or if there is a constant phase difference between waves from each of the sources

9. Stationary waves

   • When 2 periodic travelling waves of the same frequency and amplitude moving in opposite directions meet, they interfere with each other. The resulting wave formed is called a stationary wave
   • Frequency and wavelengths of a stationary wave
     • The distance between 2 consecutive nodes = λ/2
     • The distance between 2 consecutive antinodes = λ/2
     • The distance between an antinode and the next node = λ/4
   • The inter-nodal distance is the points between the points on a stationary wave that are at rest

10. Doppler Effect

    • The apparent change in the frequency of waves due to the motion of the source or the observer is called the Doppler effect
    • f =f(1)c/c±u
      • f = observed frequency
      • f(1) = actual frequency of source
      • c = speed of light in medium
      • u = speed of the source

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