Today we will talk about the use of interference in science and everyday life, reveal the physical meaning of this phenomenon and tell about the history of its discovery.
Definitions and Distributions
Before talking about the significance of a particular phenomenon in nature and technology, for a start it is necessary to give a definition. Today we are considering a phenomenon that students learn in physics classes. Therefore, before describing the practical application of interference, we turn to the textbook.
To begin with, it should be noted that this phenomenon applies to all types of waves: those that arise on the surface of the water or during research. So, interference is an increase or reduction in the amplitude of two or more coherent waves, which occurs if they occur at one point in space. Maxima in this case are called antinodes, and minima are called nodes. In this definition, some properties of oscillatory processes appear, which we will reveal a little later.
The picture that results from the superposition of waves on each other (and there can be a lot of them) depends only on the phase difference, in which the oscillations arrive at one point in space.
Light is also a wave
Scientists came to this conclusion already in the sixteenth century. The foundations of optics as a science were laid by the world famous English scientist Isaac Newton. It was he who first realized that light consists of certain elements, the quantity of which depends on its color. The scientist discovered the phenomenon of dispersion and refraction. And he was the first to observe the interference of light on the lenses. Newton studied such properties of rays as the angle of refraction in different media, birefringence, polarization. He owes the merit of the first application of wave interference for the benefit of mankind. And it was Newton who understood that if there were no light, he would not have shown all these characteristics.
Properties of light
The wave properties of light include:
- Wavelength. This is the distance between two adjacent maxima of one oscillation. It is the wavelength that determines the color and energy of visible radiation.
- Frequency. This is the number of full waves that can occur in one second. The value is expressed in Hertz and inversely proportional to the wavelength.
- Amplitude. This is the “height” or “depth” of the wobble. The value changes directly with the interference of two oscillations. The amplitude shows how strongly the electromagnetic field was indignant in order to generate this particular wave. She also sets the field strength.
- Phase of the wave. This is the part of the oscillation that is being achieved at a given time. If two waves meet at the same point during interference, then their phase difference will be expressed in units of π.
- Coherent called electromagnetic radiation with the same characteristics. The coherence of two waves implies the constancy of their phase difference. Natural sources of such radiation do not exist, they are created only artificially.
The first application is scientific
Sir Isaac worked hard and hard on the properties of light. He watched exactly how the beam of rays behaves when they meet with a prism, cylinder, plate and lens from different refracting transparent media. Once, Newton put a glass convex lens on a glass plate with a curved surface down and directed a stream of parallel rays onto the structure. As a result, radially bright and dark rings diverged from the center of the lens. The scientist immediately guessed that such a phenomenon could be observed only if there was some periodic property in the light, which somewhere extinguishes the beam, and somewhere, on the contrary, strengthens it. Since the distance between the rings depended on the curvature of the lens, Newton was able to approximately calculate the wavelength of the oscillation. Thus, the English scientist for the first time found concrete application to the phenomenon of interference.
Slot interference
Further studies of the properties of light required the formulation and conduct of new experiments. At first, scientists learned how to create coherent bundles from fairly heterogeneous sources. To do this, the flow from the lamp, candle or the sun was divided into two using optical devices. For example, when a beam hits a glass plate at an angle of 45 degrees, part of it is refracted and passes on, and part is reflected. If using these lenses and prisms to make these flows parallel, the phase difference in them will be constant. And so that in experiments the light did not come out as a fan from a point source, the beam was made parallel with the help of a close-focus lens.
When scientists learned all these manipulations with light, they began to study the phenomenon of interference on a variety of holes, including a narrow slit or a series of slits.
Interference and diffraction
The experience described above was made possible due to another property of light - diffraction. Overcoming an obstacle small enough to compare with the wavelength, the oscillation is able to change the direction of its propagation. Due to this, after a narrow slit, part of the beam changes the direction of propagation and interacts with rays that did not change the angle of inclination. Therefore, the application of interference and diffraction cannot be separated from each other.
Models and Reality
Until that moment, we used the model of an ideal world in which all the light beams are parallel to each other and coherent. Also, in the simplest description of interference, it is implied that there are always radiation with the same wavelengths. But in reality, this is not so: light is most often white, it consists of all the electromagnetic waves that the sun provides. This means that interference occurs according to more complex laws.
Thin film
The most obvious example of this kind of light interaction is the incidence of a light beam on a thin film. When there is a drop of gas in a city puddle, the surface shimmers with all the colors of the rainbow. And this is a consequence of just interference.
Light falls on the surface of the film, is refracted, falls on the boundary of gasoline and water, is reflected, and is once again refracted. As a result, at the output the wave meets with itself. Thus, all waves are extinguished, except for those for which one condition is fulfilled: the film thickness is a multiple of a half-integer wavelength. Then, at the output, the oscillation will meet with itself by two maxima. If the coating thickness is equal to the whole wavelength, then at the output a maximum will be superimposed on the minimum, and the radiation will extinguish itself.
From this it follows that the thicker the film, the greater should be the wavelength that will come out of it without loss. In fact, a thin film contributes to the separation of individual colors from the entire spectrum and can be used in technology.
Photo Shoots & Gadgets
Oddly enough, some applications of interference are familiar to all fashionistas in the world.
The main work of a beautiful model girl is to look good in front of the cameras. A whole team is preparing for the photo session of women’s professionals: a stylist, make-up artist, clothing and interior designer, magazine editor. Annoying paparazzi can trap a model on the street, at home, in funny clothes and an absurd pose, and then put the pictures on public display. But for all photographers, good equipment is important. Some devices can cost several thousand dollars. Among the main characteristics of such equipment, optics enlightenment will necessarily be listed. And the pictures from such a device will be of very high quality. Accordingly, a star shot without preparation will also not look so unattractive.
Glasses, microscopes, stars
The basis of this phenomenon is interference in thin films. This is an interesting and common phenomenon. And light interference finds application in the technique that some hold in their hands every day.
The human eye perceives the green color best. Therefore, photographs of beautiful girls should not contain errors in this region of the spectrum. If a film with a specific thickness is applied to the surface of the camera, such equipment will not have glare of green color. If an attentive reader had ever noticed such details, then he should have been struck by the presence of only red and purple reflections. The same film is applied to the glasses.
But if it is not a human eye, but a dispassionate device? For example, a microscope should record the infrared spectrum, and a telescope should study the ultraviolet constituents of stars. Then an antireflection film of a different thickness is applied.