Waves

Here is a link to know more about waves. The notes provided are easy to understand and will prove to helpful.

Click below:
Chapter 1 Form 5- Waves

Video on Waves

Here is a video that I found that explains about waves. It is very informative and useful as it is conveyed like an e-lesson. 

Part 1

*The remaining parts can be found at the related videos section on the video's Youtube page. Enjoy! 

Physics Form 5: Chapter 1 - Electromagnetic Wave

An electromagnetic wave consists of vibration perpendicular of magnetic and electric fields.

Properties of electromagnetic wave:

-They can transfer energy from one point to another.
-They are transverse wave
-They can travel through vacuum
-They travel at the same speed of the light
-They can be polarised
-They all show reflection, refraction, interference and diffraction

Physics Form 5: Chapter 1 - Application of Destructive Interference

Noise Cancellation

Noise cancellation is a method to reduce or completely cancel out undesirable sound.
A noise-cancellation speaker emits a sound wave with the same amplitude, frequency but anti-phase with the original sound.
The waves will combine each other in a process called destructive interference, eventually the waves will cancel each other and there would be no sound.
The sum of the waves is equal to zero.

Application of noise cancellation: Headphone - people working near aircraft or in noisy factories can now wear these electronic noise cancellation headsets to protect their hearing.
Cars - The way it works is that a microphone connected to the car stereo system picks up all the sound inside the car, including music or such from the stereo. Then the noise-cancellation system subtracts the sound of the music coming from the stereo and produces noise-canceling sound waves that match the frequency of unwanted sound.
Aircraft - The system uses microphones to pick up the vibrations due to jet's engine in the cabin walls. It then analyzes the signals and generates counter vibrations in the walls to produce a net result of zero vibrations.

Physics Form 5: Chapter 1 - Application of Reflection of Sound

Echoes are caused by the reflection of sound. A sound wave will continue to bounce around or reverberate until it has lost all its energy. A wave has some of its energy absorbed by the objects it hits. The rest lost as heat energy.

The phenomenon of the reflection of sound is used to determine the distance between the two objects, for example depth of seabed, depth of cave or width of a valley. The type of sound used must be ultrasound.

Sonar (Sound Navigation and Ranging). Sonar is used to detect underwater objects (corals / fishes) or to determine the depth of the water by means of an echo. Sonar equipment emits a high frequency sound signal which is reflected by the object in the water. The reflected sound wave is received by the sonar receiver. The time taken for the echo to return is used to determine the distance of the object below the water surface.


Sonar waves of high frequency is used because it possesses more energy, high penetration power and can travel further through water.

Physics Form 5: Chapter 1 - Loudness of Sound

2. Loudness - Amplitude

The loudness of a sound depends on the wave's amplitude.
The louder the sound, the higher the amplitude. So, amplitude is also a way of measuring the energy has.


The higher the energy, the higher the amplitude resulting a louder sound.


The system used to measure the loudness of sounds is the decibel system, given the unit dB.

Range (dB)	Description	Examples
0 - 30	Very Quiet	This is the threshold of human hearing, up to the sound of a quiet whisper.
31 - 50	Quiet	This is an average quiet house, with maybe the sound of a fridge running or someone moving around.
51 - 70	Normal	Regular daily sounds like people talking.
71 - 90	Loud	This is the point where a sound becomes annoying or distracting. Vacuums or a noisy car on a busy street are at these levels.
91 - 110	Very Loud	Most people will try to avoid being in areas this loud. Prolonged exposure can cause permanent ear damage. Temporary effects, like "stereo hiss", may happen.
111 +	Painful!!!	Even limited exposure to levels this high will cause permanent hearing loss.

Amplifier is a device to increase the loudness of sound by use of an external energy source. It drives the loudspeakers used in PA system to make the human voice louder.

Physics Form 5: Chapter 1 - Pitch of the Sound

Generally, there are three characteristics of sound:

• frequency affects pitch of the sound
• amplitude affects loudness of the sound
• wave form affects quality of the sound

1. Frequency - Pitch

The frequency of a wave is measured as the number of complete vibrations of particles of a medium per unit time. A commonly used unit for frequency is Hertz.

Pitch is an auditory sensation in which listener assigns musical tones to relative positions on a musical scale based on the frequency of sound. A high pitch sound corresponds to a high frequency sound wave and low pitch sound corresponds to a low frequency sound wave.



Changing Pitch:

A string vibrates with a particular fundamental frequency. However, it is possible, to produce pitches with different frequencies from the same string. The 4 properties of the string that affect its frequency are length, diameter, tension and density. The properties are as described:

• When the length of a string is changed, it will vibrate with a different frequency. Shorter strings have higher frequency and therefore higher pitch.
• Diameter is the thickness of the string. Thick strings with large diameters vibrate slower and have lower frequencies than thin ones.
• Tightening the string gives it a higher frequency while loosening it gives it a lower frequency. 
• The density of a string also affects its frequency. The denser the string, its molecules vibrate slower and its frequency will be lower. 

Name	Frequency Range (Hz)	Characteristics
Infrasonic	0 - 20	Very low frequencies of sound that the human ear can’t detect, but you mayfeel the rumbling of the waves through your body.
Sonic (AKA Audio)	20 - 20 000	Normal range for human ears, although not everyone (especially the elderly) will hear to the extremes of this range.
Ultrasonic	20 000 +	Beyond normal hearing for humans, although some animals (like dogs) hear part ways into this range. Also used in medicine (e.g. ultrasounds for pregnant women).

Physics Form 5: Chapter 1 - Interference of Waves

• Interference is the effect of superposition of two waves from two coherent sources.
• Coherent waves are the waves that can produce same frequency, same amplitude and same phase ( or with constant phase difference ).
• The  principle of superposition states that when two waves meet at the same point, the resultant displacement at that point is equal to the vector sum of the displacements produced by the individual waves at that point.

• The constructive interference occurs when two crests or two troughs meet each other.

• The destructive interference occurs when a crest meets a trough.
• Anti-nodal line is a line joining all the constructive interference points 
• Nodal line is a line joining all the destructive interference points

Physics Form 5: Chapter 1 - Diffraction

• Diffraction is the spreading of a wave as it goes through a narrow gap or passes round a small obstacle.
• The effect of diffraction increases when the width of the gap is decreased.



• The effect of diffraction increases when the wavelength is increased.
• Application of diffraction in sea waves 

Physics Form 5: Chapter 1 - Refraction of Sound Wave

• During the day, the layers of air near the ground is warmer than the layers of air higher up.
• Air layer near the ground is less dense.
• Therefore, sound wave is bent toward the normal.

•  At night, the layers of air near the ground is cool faster than the layers of air higher up.
•  Air layer near the ground is denser.
• Sound travels faster in warm air than in cool air resulting increasing of wavelength.
• When the angle of incidence is larger than the critical angle, total internal reflection occurs.
• Therefore, the path of the sound curves reflects downwards and you can hear the sound easily at night.

Click on the diagram below to play! 

Physics Form 5: Chapter 1 - Shape of the Coastline due to Wave Refraction

• In the centre of the ocean, the wavefronts are straight and parallel to each other. This is because the water waves travel at uniform speed as the depth of the sea water is uniform.
• When the waves reach the coast, the water is shallower.
• Wave speed is reduced and refraction occurs. The wavefronts are refracted and become closer to each other. Wavelength decreases.  
• Refraction causes the wavefronts to be bent towards the normal.

• Wave refraction causes wavefronts to parallel the shape of the coastline as they approach shore.
• Wave refraction also causes wave energy to converge at cape and resulting erosion.
• Wave energy diverges at bay and spreads out to a wider region, resulting deposition of sand. Therefore, amplitude of waves at the bay is smaller than at the cape.

Physics Form 5: Chapter 1 - Refraction of Water Waves

• Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.
• The most significant property of water that would affect the speed of waves travelling on its surface is the depth of the water
• Water waves travel fastest when the medium is the deepest. Thus, if water waves are passing from deep water into shallow water, they will slow down.
• This decrease in speed will also be accompanied by a decrease in wavelength.
• So as water waves are transmitted from deep water into shallow water, the speed decreases, the wavelength decreases, and the direction changes.

Click on the diagram below to play!

Physics Form 5: Chapter 1 - Reflection of Water Waves

There are two laws of reflection.
Law 1 
The normal and the incident and reflected rays are coplanar. They lie in the same plane.

Law 2 

The angle of incidence, i = the angle of reflection, r

Reflection of Circular Wave

Physics Form 5: Chapter 1 - Resonance

• Resonance occurs when the forced frequency of an external agent equals the natural frequency of the oscillating system.
• When resonance occured, it produces maximum amplitude of vibration.

Resonance can be proved by Barton Pendulum experiment

Resonance causes Tacoma Bridge to collapse

Physics Form 5: Chapter 1 - Properties of Wave

• Amplitude, A  is the maximum displacement of a particle from the equilibrium position. The amplitude is a measure of energy carried by the wave. The higher the wave energy, the higher the amplitude.
• Wavelength is the distance between two adjacent crests or troughs.
• Period, T  is the time taken for a complete oscillation of a particle of a wave.

• Frequency, f  is the number of complete oscillations performed by a particle of a wave in one second.

Physics Form 5: Chapter 1 - Wavefront

A wavefront is a line that joins all the points vibrating in-phase, such as a line passing through similar wave crests.

• Plane Waves

• Circular Waves

With wavefront, we are able to find the displacement.