If a large number of Fresnel zones fit into the hole, then to find their total action, it is necessary to take into account the decrease in the amplitude of oscillations from more distant zones. It can be shown that in this case, the intensity of the wave is equal to the intensity created by the combined action of half of the first Fresnel zone and half of the last. Zones. At large values of the number of zones on the hole, the amplitude of the oscillation from the half of the last zone becomes so small that its influence in comparison with the action of half of the first zone can be neglected. The result is as if the wave from one point to another propagates in a straight line inside a cylinder whose diameter is less than the diameter of the first zone. In this case, the concept of a light beam can be used.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.