Английский язык. Ч.3 (Units 9,10). Ильичева Н.А - 9 стр.

(8;…)
    Light can be considered as an electromagnetic wave. The wave theory has
explained a wide range of phenomena one of which is dispersion. The angle of
refraction of light depends somewhat on the light’s frequency or wavelength.
The fact that different frequencies are refracted at slightly different angles
is called dispersion. When white light (electromagnetic radiation containing all
wavelengths visible to the human eye) passes through a glass prism, the light
rays are refracted on entering the glass. The amount of refraction is a function of
the wavelength with the shortest wavelengths being deviated from their path by
the greatest amount. Violet light has a shorter wavelength than red light. A
prism used in this fashion produces the visible color spectrum, and we say the
white light has been dispersed. A diamond is said to have “fire” because of
colorful dispersion, in addition to having brilliance due to internal reflection.


(9;…)
    All waves – sound, light and so on deviate from a straight-line path when
they pass through a narrow slit. The effect also occurs when light from a fairly
bright source passes the edge of an opaque object. The deviation of light
waves is referred to as diffraction. We are well aware that sound waves bend
around everyday objects while light waves do not. If we hold a newspaper in
front of our face and speak, the sound of our voice can be heard, but our face
can not be seen. The phenomenon of diffraction and the ratio of �ld help to
explain why. We know that audible sound waves have wavelengths of
centimeters to meters, while visible light waves have wavelengths of around
10–6 m. Ordinary objects have dimensions of centimeters to meters. Thus we get
                         �� �                       ���
                         � �          � 10�6 �� 1 ; � �           � 1.
                         � d �light
                              visible               � d � audible
                                                          sound

From these statements we see that diffraction readily occurs for audible sound
but not for visible light.
                                              9