A wave is defined as a vibration that propagates through a medium, in the form of solids, liquids, and gases. Waves are vibrations that propagate. The ideal form of a wave will follow a sinusoidal motion in the form of repeated smooth oscillations.
In addition to electromagnetic radiation, waves are also present in the medium in which they can travel and can transfer energy from one place to another without causing the particles of the medium to move permanently; ie there is no mass transfer. Each special point oscillates around one particular position.
There are two kinds of waves, namely: sound waves and light waves. Sound waves are used in Ultrasonography or ultrasound technology, to find out the condition of the fetus in the womb.
Then, what about light waves? Before a deeper discussion, it is best to first know the definition of light.
Light is wave electromagnetic spectrum with a limited spectrum (optical spectrum or visible spectrum), in which certain electromagnetic waves can be seen which we then refer to as light.
There is no exact limit on the optical spectrum, but the normal human eye can receive/perceive electromagnetic waves with wavelengths between 400 and 700 nm (which we call visible light).
Besides light is a wave, light can also be said to consist of particles called photons. The direction of vibration of light is perpendicular to the direction of its propagation, so light waves are categorized as transverse waves.
Light Wave Characteristics
Light waves have four special characteristics, namely:
- Light waves can propagate in a vacuum and without any medium, because they are electromagnetic waves.
- Light waves are transverse waves, whose direction of propagation is perpendicular to the direction of vibration.
- Light waves can be reflected if they hit a field, whether flat or not.
- Light waves can be passed through a gas, water, or solid medium.
Properties of Light Waves
Light waves have several characteristics, including:
Straight Vine
The nature of light on this one seems to be the most common trait that is the easiest to find. Naturally or naturally light will have a straight direction of propagation, if you want to prove it, you can try turning on a flashlight, laser or flashlight on a smart phone. Note the light can change if there is interference from external factors such as the propagation medium or from the movement of the light source.
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For example, light waves undergoing refraction make a pencil in a glass filled with water appear to be broken or bent. (Unsplash)
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Refraction (Refraction)
Refraction is a change in the direction of incident light that propagates from one medium to another, refraction usually occurs because of a difference in refractive index, and the magnitude of the resulting change in direction depends on the refractive index of the two mediums. The example that is most often found is a straw in a glass filled with water that looks as if it is broken, this is because air and water have different refractive indices.
Absorbable (Absorption)
When a transparent material or material is exposed to light, then some of the energy from the light will be dissipated (reduced) by the material or material into heat energy. This happens naturally to our eyes, to see colors around us.
Can Penetrate Clear Objects
Light can penetrate clear objects, the most common example is a house lamp. Light can penetrate the glass in the house light bulb so that it can illuminate one room of the house.
Decomposable (Dispersion)
Dispersion is the refraction of white light (polychromatic light) into its components, namely monochromatic light. Dispersion will occur when white light passes through a refracting field.
We can observe this property of light by using a prism as a refracting field. In a prism, the incoming light will be refracted twice, namely when it enters the prism and when it leaves the prism.
Rainbow is one example of light dispersion that we can observe naturally. Rainwater refracts sunlight so that light is dispersed into various visible lights which we call a rainbow.
Light Interference
Light interference is the sum of the superposition of two or more light waves that can cause the formation of other waves.
Light interference is divided into two, namely double slit interference and thin film interference.
Interference has two contradictory properties, namely building or called constructive interference and destructive interference or called destructive interference. As a result of these two properties, light interference has 2 patterns, namely light patterns and dark patterns.
- Light Patterns are generated due to constructive or mutually reinforcing superpositions.
- Dark Patterns are generated due to destructive or mutually weakening superpositions.
For interference to occur, two conditions are required:
- The light source must be coherent, that is, the phase is fixed (with respect to each other) and the frequency is the same
- The light source must be monochromatic, that is, it has only a single wavelength
- Light interference in double slit
Light interference in the double slit occurs because of the difference in the phase of light from the light that passes through the two slits. When a light source with exactly the same frequency and wavelength passes through two slits, there will be a superposition that causes dark and light lines to appear on the screen.
Since the wave superposition has an interference angle, the equation can be written as:
Look at the picture above, if the angle is very small (sin tan so that the value of sin is y/l, then the equation becomes:
Brightness pattern:
Dark pattern:
d = distance between slits (m)
= interference angle
m = orde (0,1,2,…)
λ = wavelength (m)
y = distance of m-order band to center light (m)
l = slit distance to screen (m)
- Interference on Thin Membranes
As the name implies, this interference occurs in thin layers such as soap and oil. In this experiment, it was found that if monochromatic light hits a thin layer, some of the light will be reflected and some will be refracted and then reflected again, the combination of the two will cause interference.
A ray of light comes on a thin film and forms an angle i, then some of the light is reflected at the top to form a reflection AE, and some is refracted to form ABC and then both of them interfere with each other to point P.
Equation for maximum interference at P (bright pattern)
Equation for minimum interference at P (dark pattern)
d = layer thickness
n = refractive index of thin layer
r = angle of refraction of the ray
= wavelength of light
m = order of interference
Light Diffraction
Diffraction is the bending of light when light passes through a slit so that light will be broken up into smaller parts and have new light properties.
When light passes through a very small slit, dark and light bands can form, which is known as single slit diffraction. After light passes through the slit, new light is formed (by considering the slit as a new light source) which spreads in all directions.
In single slit diffraction, the bright band will cover one m-order. Then the equation becomes:
For bright bands:
For dark tape:
- Diffraction on the grating (Multiple Gap)
If a monochromatic light is passed through a grating plate or multiple slits, a diffraction pattern will be formed in the form of a dark and light pattern on the screen. A grid is an arrangement of parallel slits of equal size, and can be made by making scratches on a glass or metal plate using a diamond tip.
The relationship between the number of slits and the distance between the slits is formulated as:
N = lattice constant (lines/m)
In multiple slit diffraction, the bright and ring patterns are the same as the interference.
For bright bands:
For dark tape:
Light Polarization
Polarization of light is a decrease in the intensity of light caused by a reduction in the components of the light wave. Polarization can only occur in transverse waves. Polarization of light can occur due to reflection, refraction, absorption and scattering.
- Polarization due to refraction:
If the reflected ray is perpendicular to the refracted ray, then the reflected ray will be polarized. The magnitude of the polarization angle can be calculated by the equation:
Description:
ip = polarization angle
n2 = objective refractive index
n1 = original refractive index
- Polarization due to absorption:
If the light intensity is polarized, then after passing through the first polarizer, the equation for the light intensity becomes:
Where:
I1 = light intensity after passing through the polarizer
I0 = intensity of light source
Light Utilization
One of the many uses of light is on television. Currently, existing televisions have a thin size and produce high-quality (HD) and 3D images.
There are LCD TVs and LED TVs, LCD TVs are generally made of two layers of fine material that are polarized and bonded to each other.
One of the layers is wrapped with a special polymer that holds each individual liquid crystal. Then electronic energy is channeled through each crystal allowing the Crystal to block light to produce an image.
In order for the image produced by the LCD to be seen by the viewer, a fluorescent light bulb is needed.
LCD utilizes Liquid Crystal Display technology. This type has two layers of glass that are polarized and stick together.
There is a liquid crystal contained in one layer. This liquid serves to pass or block light to produce an image on the screen when an electric current passes through it.
But the crystal does not produce its own light, the light comes from a series of fluorescent lights behind the screen. With the help of neon lights, the image created by the crystal can be seen.
Meanwhile, on LED TVs there are two types of technology, namely Full LED and Edge LED. The light source used previously is converted from a lamp to an LED, so that the picture is clearer. Because the LEDs are more focused and do not flicker.
Application of Light Wave
The application of the principle of light waves is widely used in everyday life. For example in the field of technology.
Gamma rays
Gamma rays are widely used in the world of medicine such as for diagnosing and treating cancer, and also assisting developments in the fields of astronomy and physics. Gamma rays have a frequency between 93 Hz with a wavelength between 94 cm to 95 cm.
Radar
Radar is a tool to detect the presence or location, speed, and direction of objects from a distance. Radar is generally used for navigation and guidance systems. Radar also produces radio frequency radiation and much more.
X-ray
Have you ever accompanied your relatives or experienced yourself to the hospital doing radiographs to see if there were any broken or cracked bones? If so, you should be grateful for the existence of x-rays because this makes it much easier for medical personnel to check a person’s condition without having to dissect them first. X-rays have a frequency of 96 Hz to 93 Hz. The wavelength is very short, i.e. 98 cm – 99 cm.
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