Answer the expanded visible light portion of figure

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Answer: The expanded visible-light portion of Figure 6.4 tells you that red light has a longer wavelength than blue light. The lower wave has the longer wavelength (lower frequency) and would be the red light. (b) The electromagnetic spectrum ( Figure 6.4 ) indicates that infrared radiation has a longer wavelength than visible light. Thus, the lower wave would be the infrared radiation. Solution (a) The lower wave has a longer wavelength (greater distance between peaks). The longer the wavelength, the lower the frequency ( ν = c/ λ ). Thus, the lower wave has the lower frequency, and the upper one has the higher frequency.
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SAMPLE EXERCISE 6.2 Calculating Frequency from Wavelength The yellow light given off by a sodium vapor lamp used for public lighting has a wavelength of 589 nm. What is the frequency of this radiation? Solution Analyze: We are given the wavelength, λ  of the radiation and asked to calculate its frequency, ν . Plan: The relationship between the wavelength (which is given) and the frequency (which is the unknown) is given by Equation 6.1. We can solve this equation for ν and then use the values of λ and c to obtain a numerical answer. (The speed of light, c , is a fundamental constant whose value is given in the text or in the table of fundamental constants on the back inside cover.) PRACTICE EXERCISE (a) A laser used in eye surgery to fuse detached retinas produces radiation with a wavelength of 640.0 nm. Calculate the frequency of this radiation. (b) An FM radio station broadcasts electromagnetic radiation at a frequency of 103.4 MHz (megahertz; MHz = 10 6 s –1 ). Calculate the wavelength of this radiation. Solve: Solving Equation 6.1 for frequency gives ν = c/ λ . When we insert the values for c and λ , we note that the units of length in these two quantities are different. We can convert the wavelength from nanometers to meters, so the units cancel: Check: The high frequency is reasonable because of the short wavelength. The units are proper because frequency has units of “per second,” or s –1 . Answers: (a) 4.688 × 10 14 s –1 , (b) 2.901 m
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