By MICHAEL JOHN UGLO
WELCOME again to this lecture (No 14) in the Science in Action series.
Our topic is on Waves as taught in science, particularly physics in this country. There is immense application of this scientific study as the world is currently living in technology and science.
In pertinence, as so much of a blessing as its use of its applications in technology for the good of the society, there is a counter-productive and evil use as people are using waves in the sense of science and physics to the detriment of moral values nourishment and prosperity. That is prostitution, adultery and corruption (deeds to derail from justice) is on the rise.
Control of a person’s mindset and fear of doing bad with its adverse consequences to uphold dignity of a person’s life is paramount and should take priority over greed, fame and selfishness.
The text messages and mobile phone communications you have every day come to you in the form of a wave. Waves are studied in physics. Waves can also be calculated in physics as well as mathematics as a signal. Waves come in many forms, includinh tidal waves, sound waves, seismic waves, gravity waves, electromagnetic waves, gravitational waves, plasma waves and terahertz waves.
Waves are a travelling disturbance in space from an equilibrium point. Therefore, a wave can be travelling. Also, a wave can be static known as a static wave. Waves as studied in physics today are based on mechanical waves and electromagnetic waves and also wave probabilities from quantum mechanics. The travelling waves generate energy, momentum and information.
The two most important parts to be studied about waves are the time or the period of the wave propagation and the next is the frequency at which this propagation occurs. Mechanical waves are generated as a result of strain or deformation happening in a medium of particles. As a result, it creates stresses in the nearby particles which create further stress and so on.
This sends a wave of particles in motion. The mechanical waves can generate any of the two forms of waves known as longitudinal and transverse waves. Whether mechanical or electromagnetic, the magnitude of the wave can be calculated if it is in a linear wave form.
A linear waveform can be a harmonic wave which is sinusoidal or simply a sine wave or a complex waveform called a superimposed wave form from which a method called Fourier analysis can be used to find the wave’s components of sinusoids, frequencies and wavelengths to be analysed. If a wave form is non-linear, then a Fourier analysis cannot be used because it will be very complex to work out. All wave forms travel in a form of a sinusoidal wave form and have nodes at the standing points. The standing points maintain the equilibrium points of wave at a constant amplitude and also at a constant wavelength.
Sinusoidal waveform or Sine wave. Picture from electronics-tutorials.ws
Mechanical waves can produce transverse waves on a linear medium such as the vibrations on a string. The direction of travel together with the direction of the wave propagation are perpendicular to each other. Perpendicular means that they are at right angles to each other. Another mechanical wave that produces longitudinal wave is a sound wave. Variations in the local pressures of particles that propagating through space creates the sounds of different tones. These particles actually travel in the direction of the wave motion and are therefore said to be longitudinal.
The electromagnetic waves are all transverse waves meaning they propagate in space with the constituent particles acting at right angles or perpendicular to each other. The two parts to an electromagnetic wave are the electric fields and the magnetic fields. There are many electromagnetic waves and namely the radio waves, microwaves, the terahertz wave, the infrared wave, the visible light, ultraviolet wave, the X-ray and the gamma ray waves.
The change in electric fields creates a magnetic current and a change in magnetic field creates an electric current. They propagate in that mode and travel at the speed of approximately 3×108 meters per second. They can travel in a vacuum and do not require a medium to travel in like the other waves.
The waves can change their speed when they travel from air which is one medium of one density to another medium say a transparent glass of another medium.
Air is less dense than a glass so its speed will be slower. That means with the incident light and the normal point to the glass will be the points where the light passing through will bend. It will bend towards the normal because the glass is more, dense than air. The bending of light as described here is called refraction. When we reverse the scene, as light now is made to come out from the glass into the air, that is light travelling from a more, dense medium (glass) to a less dense medium (air) then, light will bend away from the normal.
In refraction, it is relevant to find the refractive index of the medium it is coming into contact with to see how much of a refraction can be measured. Snell’s law of refraction is normally used here. The formula is, n1/n2 = sin α2/sin α1 where n1 is the first medium and n2 is the second medium. Sin a1 and sin a2 are the sines of the angle of the first and the second medium respectively. The following is a diagrammatic representation:
Snell’s law is defined as “The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given colour and for the given pair of media”. Snell’s law formula is expressed as:
Sin i sin r = constant = μ
In diffraction, light is made to spread at the corners where the wavelength of the travelling wave encounters an obstacle or either an opening called an aperture that allows the wave to bend around the corner or the edge. The aperture and the obstacle become the secondary source of generation of the propagating wave.
Waves get reflected as well. When they fall on or incident on a surface that does not absorb any light, they reflect all the light back.
This is called reflection of light. They take the form of the perfect mirror to reflect all light rays and waves back. The three laws of reflection are 1. The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal. 2. The incident ray, the normal and the reflected ray are all in the same plane. 3. Incident ray and refracted ray are on different sides of the
normal. These laws are applied to all flat, curved, concave and all convex mirrors.
In mathematics a wave can be calculated using the function F(x,t). The F takes the function form while x is a particular point when the particle is taken at a rest position. The t takes the form of a particular time at which the particle is resonating. Normally the highest amplitudes of a group wave is considered for this calculation. In the instance where you have to have several a total amount say a total of a echo of radar from an air plane is measured, then you will include the mediums or families of waves in the equation such as F(A,B…; x,t) to include those families.
A water wave is an example of a standing wave travelling to derive the equilibrium. Such waves come under gravity waves whereby two mediums are generating waves to maintain equilibrium. Gravitational waves are rather different because, they are a disturbance in the space time in the universe as is contained in the Relativity theory.
My prayer for PNG today is; “Awake from your slumber. Arise from your sleep. A new day is dawning, for all those who weep. Let us build the city of God. May our tears be turned into dancing. The One who has loved us, has brightened our way…”
Next week: The sciences of Communication and technology
• Michael Uglo is the author of the science textbook “Science in PNG, Pacific, Asia & Caribbean” and a lecturer in Avionics, Auto- Piloting and Aircraft Engineering. Please send comments to: [email protected]