PROPAGATION OF LIGHT

1-25 This phenomenon occurs whenever the frequency of vibrations is the same as the natural frequency of a cavity, and is called RESONANCE. Noise The most complex sound wave that can be produced is noise. Noise has no tonal quality. It distracts and distorts the sound quality that was intended to be heard. NOISE is generally an unwanted disturbance caused by spurious waves originating from man-made or natural sources, such as a jet breaking the sound barrier, or thunder. Q26. What term is used in describing the science of sound? Q27. A sound wave that is reflected back toward the source is known as what type of sound? Q28. What is the term for multiple reflections of sound waves? Q29. A cavity that vibrates at its natural frequency produces a louder sound than at other frequencies. What term is used to describe this phenomenon? Q30. What do we call a disturbance that distracts or distorts the quality of sound? LIGHT WAVES Technicians maintain equipment that use frequencies from one end of the electromagnetic spectrum to the other—from low-frequency radio waves to high-frequency X-rays and cosmic rays. Visible light is a small but very important part of this electromagnetic spectrum. Most of the important terms that pertain to the behavior of waves, such as reflection, refraction, diffraction, etc., were discussed earlier in this chapter. We will now discuss how these terms are used in understanding light and light waves. The relationship between light and light waves (rays) is the same as sound and sound waves. Light is a form of energy. It can be produced by various means (mechanical, electrical, chemical, etc.). We can see objects because the light rays they give off or reflect reach our eyes. If the object is the source of light energy, it is called luminous. If the object is not the source of light but reflects light, it is called an illuminated body. PROPAGATION OF LIGHT The exact nature of light is not fully understood, although scientists have been studying the subject for many centuries. Some experiments seem to show that light is composed of tiny particles, and some suggest that it is made up of waves. One theory after another attracted the approval and acceptance of physicists. Today, some scientific phenomena can be explained only by the wave theory and others only by the particle theory. Physicists, constantly searching for some new discovery that would bring these two theories into agreement, gradually have come to accept a theory that combines the principles of the two theories. According to the view now generally accepted, light is a form of electromagnetic radiation; that is, light and similar forms of radiation are made up of moving electric and magnetic fields. These two fields will be explained thoroughly later in this chapter.