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8.2: The Nature of Light

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     with various forms of radiant, or transmitted, energy, such as the energy associated with the visible light we detect with our eyes, the infrared radiation we feel as heat, the that causes sunburn, and the x-rays that produce images of our teeth or bones. All these forms of radiant energy should be familiar to you. We begin our discussion of the development of our current atomic model by describing the properties of waves and the various forms of electromagnetic radiation. is a periodic oscillation that transmits energy through space. Anyone who has visited a beach or dropped a stone into a puddle has observed waves traveling through water (Figure \(\PageIndex{1}\)). These waves are produced when wind, a stone, or some other disturbance, such as a passing boat, transfers energy to the water, causing the surface to oscillate up and down as the energy travels outward from its point of origin. As a passes a particular point on the surface of the water, anything floating there moves up and down. —between the midpoints of two peaks, for example, or two troughs—is the (\(λ\), lowercase Greek lambda). Wavelengths are described by a unit of distance, typically meters. The (\( u\), lowercase Greek nu) of a is the number of oscillations that pass a particular point in a given period of time. The usual units are oscillations per second (1/s = s), which in the SI system is called the hertz (Hz). is defined as half the peak-to-trough height; as the amplitude of a with a given frequency increases, so does its energy. As you can see in Figure \(\PageIndex{2}\), two waves can have the same amplitude but different wavelengths and vice versa. The distance traveled by a per unit time is its speed (\(v\)), which is typically measured in meters per second (m/s). The speed of a is equal to the product of its wavelength and frequency: }} \right )\left ( \dfrac{\cancel{\text{}}}{\text{second}} \right ) &=\dfrac{\text{meters}}{\text{second}} \label{6.1.1b} \end{align} \] (the water). In contrast, energy that is transmitted, or radiated, through space in the form of periodic oscillations of electric and magnetic fields is known as . (Figure \(\PageIndex{3}\)). Some forms of electromagnetic radiation are shown in Figure \(\PageIndex{4}\). In a vacuum, all forms of electromagnetic radiation—whether microwaves, visible light, or gamma rays—travel at the speed of light (), which turns out to be a physical constant with a value of 2.99792458 × 10 m/s (about 3.00 ×10 m/s or 1.86 × 10 mi/s). This is about a million times faster than the speed of sound. , with wavelengths of ≤ 400 nm, has enough energy to cause severe damage to our skin in the form of sunburn. Because the of the atmosphere absorbs sunlight with wavelengths less than 350 nm, it protects us from the damaging effects of highly energetic ultraviolet radiation. requires an understanding of the properties of waves and electromagnetic radiation. A is a periodic oscillation by which energy is transmitted through space. All waves are , repeating regularly in both space and time. Waves are characterized by several interrelated properties: (\(λ\)), the distance between successive waves; (\( u\)), the number of waves that pass a fixed point per unit time; (\(v\)), the rate at which the propagates through space; and , the magnitude of the oscillation about the mean position. The speed of a is equal to the product of its wavelength and frequency. consists of two perpendicular waves, one electric and one magnetic, propagating at the (\(c\)). Electromagnetic radiation is radiant energy that includes radio waves, microwaves, visible light, x-rays, and gamma rays, which differ in their frequencies and wavelengths.

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