# barcode scanner in asp.net web application Section 162 The Wave Nature of Light in Objective-C Maker QR Code in Objective-C Section 162 The Wave Nature of Light

Section 162 The Wave Nature of Light
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Figure 16-18 When two polarizing filters are arranged with their polarizing axes in parallel, a maximum amount of light passes through (a) When two polarizing filters are arranged with perpendicular axes, no light passes through (b)
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Polarization analysis Suppose that you produce polarized light with a polarizing filter What would happen if you place a second polarizing filter in the path of the polarized light If the polarizing axis of the second filter is parallel to that of the first, the light will pass through, as shown in Figure 16-18a If the polarizing axis of the second filter is perpendicular to that of the first, no light will pass through, as shown in Figure 16-18b The law that explains the reduction of light intensity as it passes through a second polarizing filter is called Malus s law If the light intensity after the first polarizing filter is I1, then a second polarizing filter, with its polarizing axis at an angle, , relative to the polarizing axis of the first, will result in a light intensity, I2, that is equal to or less than I1 Malus s Law I2 I1cos2
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The intensity of light coming out of a second polarizing filter is equal to the intensity of polarized light coming out of a first polarizing filter multiplied by the cosine, squared, of the angle between the polarizing axes of the two filters
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Using Malus s law, you can compare the light intensity coming out of the second polarizing filter to the light intensity coming out of the first polarizing filter, and thereby determine the orientation of the polarizing axis of the first filter relative to the second filter A polarizing filter that uses Malus s law to accomplish this is called an analyzer Analyzers can be used to determine the polarization of light coming from any source
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You place an analyzer filter between the two cross-polarized filters, such that its polarizing axis is not parallel to either of the two filters, as shown in the figure to the right 1 You observe that some light passes through
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filter 2, though no light passed through filter 2 previous to inserting the analyzer filter Why does this happen
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Filter 1
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Polarized light Analyzer
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2 The analyzer filter is placed at an angle of
relative to the polarizing axes of filter 1 Derive an equation for the intensity of light coming out of filter 2 compared to the intensity of light coming out of filter 1 Polarizing axes
Laura Sifferlin
16 Fundamentals of Light
The Speed of a Light Wave
As you learned in 14, the wavelength, , of a wave is a function of its speed in the medium in which it is traveling and its constant frequency, f Because light has wave properties, the same mathematical models used to describe waves in general can be used to describe light For light of a given frequency traveling through a vacuum, wavelength is a function of the speed of light, c, which can be written as 0 c/f The development of the laser in the 1960s provided new methods of measuring the speed of light The frequency of light can be counted with extreme precision using lasers and the time standard provided by atomic clocks Measurements of wavelengths of light, however, are much less precise Different colors of light have different frequencies and wavelengths, but in a vacuum, they all travel at c Because all wavelengths of light travel at the same speed in a vacuum, when you know the frequency of a light wave in a vacuum, you can calculate its wavelength, and vice versa Thus, using precise measurements of light frequency and light speed, you can calculate a precise value of light wavelength Relative motion and light What happens if a source of light is traveling toward you or you are moving toward the light source You learned in 15 that the frequency of a sound heard by the listener changes if either the source or the listener of the sound is moving The same is true for light However, when you consider the velocities of a source of sound and the observer, you are really considering each one s velocity relative to the medium through which the sound travels Because light waves are not vibrations of the particles of a mechanical medium, unlike sound waves, the Doppler effect of light can involve only the velocities of the source and the observer relative to each other The magnitude of the difference between the velocities of the source and observer is called the relative speed Remember that the only factors in the Doppler effect are the velocity components along the axis between the source and observer, as shown in Figure 16-19
Figure 16-19 The observer and the light source have different velocities (a) The magnitude of the vector subtraction of the velocity components along the axis between the source of light and the observer of the light is referred to as the relative speed along the axis between the source and observer, v (b) (Illustration not to scale)