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# Chapter 25 - Chapter 25 8 Picture the Problem This is a...

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Chapter 25 8. Picture the Problem : This is a units conversion problem Strategy: Use the appropriate unit conversions to measure the distance of one light year in kilometers, the speed of light in light years per year, and the speed of light in feet per nanosecond. Solution: 1. (a) Express 1 ly in km: 2. (b) Write the speed of light in lightyears per year: 3. (c) Convert the speed of light to units of feet per nanosecond: Insight: In solving problems involving the light year it is helpful to remember that the unit ly is a unity of distance, where the speed of light times one year. 12. Picture the Problem : The wavelength of light from a star that is moving toward Earth is Doppler- shifted to a shorter wavelength. Strategy: Replace the frequency in equation 25-3 with the wavelength given in equation 25-4. Solve the resulting expression for the shifted wavelength divided by the unshifted wavelength. Solution: 1 . (a) Because the star is moving toward Earth, the frequencies of the electromagnetic waves are increased. However, the measured wavelengths are less than what they would be if the star were at rest relative to us because the wavelengths are inversely proportional to the frequencies 2. (b) Write the Doppler shift in terms of wavelength: 3. Solve for the ratio of wavelength: Insight: The wavelength is shorter than it is when the star is at rest relative to Earth, as predicted. 25. Picture the Problem : Dental X-rays have a wavelength of 0.30 nm. Strategy: Solve equation 25-4 for the frequency. Solution: Calculate the frequency: Insight: This frequency falls in the X-ray part of the spectrum as described on page 848 of the text.

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Chapter 25 - Chapter 25 8 Picture the Problem This is a...

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