1. The characteristic of reflection of light enables us to see objects. Objects that do not emit light are not seen in the dark. An object only is seen if light is incident on it a reflected back to our eyes

Experiment

2. The experiment of reflection of light wave shows that reflection of light wave obeys the law of reflection.

 

1. Reflection occurs when an incident wave hits a reflector and reflected back.
2. The direction of propagation of the wave changed when it is reflected.
3. The wavelength, frequency and speed of wave remain unchanged.
4. The amplitude of the wave may or may not change depend on the material of the reflector and the shape of the wavefront.

Reflection of Straight and Circular Wave

1. Reflection of waves obeys the law of reflection, that is
   1. The angle of incident is equal to the angle of reflection
   2. The incident wave, reflected wave and the normal lie on the same plane.
2. For reflection of circular wave, the distance of image from the reflector is equal to the distance of source of wave from the reflector.

(Reflection of Straight Plane Wave)

(Reflection of Circular Wave)

 

Phenomena of Waves

1. There are 4 phenomena of waves:
   1. Reflection
   2. Refraction
   3. Diffraction
   4. Interference
2. Diffraction and interference are unique phenomena. Only waves perform these phenomena.
   
   

 

Natural Frequency

The Natural frequency of an oscillating system is the frequency of the system when there is no external force or forces acting on it.

Damping

1. Damping is the decrease of amplitude of an oscillating system.
2. An oscillating system experiences damping when its energy is losing to the surrounding as heat energy.
3. Usually, the frequency of the system remain unchanged.

(Displacement-time graph of a damped oscillation)

(Amplitude-time graph of a damped oscillation)

Type of Damping

Damping can be divided into:

1. internal damping, where an oscillating system loses energy due to the extension and compression of the molecules in the system.
2. external damping, where an oscillating system loses energy to overcome frictional force or air resistance that act on it.

Force Oscillation

1. In a damped oscillation, external force must be applied to the system to enable the oscillation to go on continuously.
2. Oscillation with the help of external force or forces is called a force oscillation.

Resonance

In a force oscillation, if the frequency of the external force is equal to the natural frequency of the system, the system will oscillates with maximum amplitude, and this is named as resonance.

Examples of Resonance

1. Opera singer breaks a wine glass with her voice due to the effect of resonance.
2. Tacoma Narrow Bridge in USA collapsed in 1940 due to the effect of resonance.
3. A moving bus produces excessive noise at certain speed when the frequency of the engine equal to the natural frequency of the bus.

Bartons Pendulum

The characteristic of resonance can be demonstrated with a Barton’s pendulum system.


Observation:
1. When pendulum X oscillates, the other pendulums are forced to oscillate.
2. Pendulum D will oscillates with the largest amplitude.

 

 

Oscillation

1. Waves are formed by a series of oscillation.
2. In order to understand waves, we must understand oscillation.

Technical Terms Related to Oscillation

1. An equilibrium position is a point where an oscillating object experiences zero resultant forces.
2. A complete oscillation occurs when the vibrating object:
   1. moves to and fro from its original position and
   2. moves in the same direction as its original motion.
      
      
      
      
      
      
3. Amplitude is the maximum amplitude of an object from its equilibrium position. The SI unit for amplitude is meter, m.
   
   
   
   
   
   
4. The greater the amplitude, the greater the mechanical energy possessed by the oscillating system.
5. Period is defined as the time required for one complete oscillation or vibration .
6. Frequency, f is the number of oscillation that take place in one second. The SI unit for frequency is Herz (Hz).
7. Frequency can be related to period by the following equation
   
   f = frequency
   T = Period
   
   

In a displacement-time graph, we can determine

1. The displacement of the oscillating object at any time.
2. The amplitude
3. The period.

Comparing Displacement-Time Graph and Displacement- Distance Graph

（Displacement-time graph - Graph of oscillation)

(Displacement-distance graph - Graph of Waves)

1. Both the displacement-time graph and the displacement distance graph looked similar. However they are 2 different types of graph.
2. The displacement-time graph illustrate the displacement of an object over time whereas the displacement-distance graph tell the position of the vibrating particles of a wave.
3. For a displacement- distance graph, the distance between 2 crest/trough represent the period whereas for the displacement-distance graph, it represents the wavelength.

 

1. A Displacement – Distance graph shows the position of each particle in a wave relative to its distance from a reference point.
2. The distance between two (2) successive crest or trough is the wavelength.
3. The maximum displacement of the particles from the equilibrium position (displacement = 0) is the amplitude.
4. The amplitude of the wave will increase as the energy transfers by the wave increase and vice versa.

 

Waves can be classified into 2 groups

1. transverse wave
2. longitudinal wave
   

Transverse Wave

Longitudinal Wave

Transverse Wave – Crest and Trough

1. When discussing wave, it’s important to know what is meant by the crest and trough of a wave.
2. The point at which the displacement of the water from its normal level is highest called the crest of the wave
3. The point at which the displacement of the water from its normal level is lowest called the trough of the wave. 

Longitudinal Wave – Compression and Rarefaction

1. Unlike transverse wave, longitudinal waves have no crest and trough, instead, they have compression and rarefaction.
2. In compression regions of longitudinal waves, wave particles of the medium are packed closer.
3. In rarefaction regions, wave particles of the medium are packed further apart.

Finding Wavelength from a Diagram

Transverse Wave

Wavelength is the distance between two successive crest or trough.

Longitudinal Wave

Wavelength is the distance between two successive compression or rarefaction.

Wave front diagram

Wavelength is the distance between two successive wave front

 

Phase

1. A phase is the current position in the cycle of something that changes cyclically.
2. Two vibrating particles are in the same phase if their displacement and direction of motion are the same.
   1. In phase – Same phase
   2. Out of phase – Different phase
   3. Anti-phase – Phase different = 180°

Wavefront

1. A wavefront is a line or a surface that connects points that are moving at the same phase and has the same distance from the source of the waves.
2. When a circular wave is formed, a circular wave front is formed.
3. Characteristics of wavefront:
   1. wavefronts are always perpendicular to the direction of wave propagation. (As shown in the diagram below)
   2. all the points on a wavefront have same distance from the source of the wave.

Wavelength

The wavelength (λ) is defined as the distance between two successive particles which are at the same phase (exactly the same point in their paths and are moving in the same direction.).

 

What is Wave?

1. A wave is a disturbance or variation that propagates through a medium, often transferring energy.
2. Waves travel and transfer energy (its amplitude) and information (its frequency) from one point to another, with little or no permanent displacement of the particles of the medium.