The body, oscillating in an elastic medium, createsA perturbation that is transmitted from one point to another and bears the name of a wave. This happens with a certain speed, which is considered the speed of its spread. That is, it is a quantity that characterizes the distance traveled by any point of the wave in a unit length of time.
Let the wave move along one of the axes(for example, horizontal). Its shape is repeated in space after a certain time, that is, the wave profile moves along the propagation axis with a velocity that has a constant value. In a time corresponding to the period of oscillations, its front will shift by a distance, called the wavelength.
It turns out, the wavelength is the same distance,which "runs through" its front for a period of time equal to the period of oscillations. For clarity, imagine a wave in the form in which it is usually depicted in the drawings. We all remember how sea waves look, for example. The wind drives them along the sea, and each wave has a crest (maximum point) and the lowest point (minimum), both of which constantly move and change one another. The points lying in one phase are the vertices of two adjacent ridges (we assume that the ridges have the same height and the motion occurs at a constant speed) or the two lowest points of neighboring waves. The wavelength is just the distance between such points (two adjacent ridges).
In the form of waves, all kinds ofenergy - thermal, light, sound. They all have different lengths. For example, passing through the atmosphere, sound waves slightly change the air pressure. The regions of maximum pressure correspond to the maxima of sound waves. Due to its structure, the human ear catches these changes in pressure and sends signals to the brain. In this way, we hear a sound.
The length of the sound wave determines its properties. To find it, you need to divide the wave velocity (measured in m / s) by the frequency in Hz. Example: at a frequency of 688 Hz, the sound wave moves at a speed of 344 m / s. The wavelength will then be 344: 688 = 0.5 m. It is known that the propagation velocity of a wave in the same medium does not change, hence its length will depend on the frequency. Low-frequency sound waves have a wavelength greater than high-frequency waves.
An example of another type of electromagneticradiation can serve as a light wave. Light is a part of the electromagnetic spectrum visible to our eye. The length of the light wave, which human eyesight can perceive, lies in the range from 400 to 700 nm (nanometers). On both sides of the visible range of the spectrum lie areas that are not perceived by our eye.
Ultraviolet waves have a length that is shorter than the length of the visible part of the spectrum. Although the human eye is not able to see them, but, nevertheless, they are capable of inflicting considerable harm on our eyesight.
The wavelength of infrared radiation is greater than the maximum length that we can see. These waves are captured by special equipment and are used, for example, in night vision cameras.
Among the rays accessible to our sight, the shortest length is a ray of purple, the largest is red. In the interval between them lies all the spectrum available to the view (remember the rainbow!)
How do we perceive colors? The rays of light, having a certain length, fall on the retina of the eye, which has photosensitive receptors. These receptors transmit signals directly to our brain, where a sense of a certain color is formed. What colors we see - depends on the wavelengths of the incident rays, and the brightness of the color sensation is determined by the intensity of the radiation.
All objects that surround us have the abilityreflect, transmit or absorb incident light (fully or partially). For example, the green color of the foliage means that most of the range reflects mainly the rays of green color, the others are absorbed. Transparent objects have the property of delaying radiation of a certain length, which is used, for example, in photography (the use of photo filters).
Thus, the color of the object tells us about the ability to reflect the waves of a certain part of the spectrum. Objects that reflect the entire spectrum, we see white, absorbing all the rays - black.
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