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Chapter 24: Q10PE (page 888)
Combing your hair leads to excess electrons on the comb. How fast would you have to move the comb up and down to produce red light?
The frequency to move the comb up and down to produce red light is \(5 \times {10^{14}}\;Hz\).
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Conversations with astronauts on lunar walks had an echo that was used to estimate the distance to the Moon. The sound spoken by the person on Earth was transformed into a radio signal sent to the Moon and transformed back into sound on a speaker inside the astronaut's space suit. This sound was picked up by the microphone in the space suit (intended for the astronaut's voice) and sent back to Earth as a radio echo of sorts. If the round-trip time was , what was the approximate distance to the Moon, neglecting any delays in the electronics?
The rate at which information can be transmitted on an electromagnetic wave is proportional CZ the frequency of the wave. Is this consistent with the fact that laser telephone transmission at visible frequencies carries far more conversations per optical fiber than conventional electronic transmission in a wire? What is the implication for ELF radio communication with submarines?
Suppose a source of electromagnetic waves radiates uniformly in all directions in empty space where there are no absorption or interference effects. (a) Show that the intensity is inversely proportional to , the distance from the source squared. (b) Show that the magnitudes of the electric and magnetic fields are inversely proportional to r .
Laser vision correction often uses an excimer laser that produces electromagnetic radiation. This wavelength is extremely strongly absorbed by the cornea and ablates it in a manner that reshapes the cornea to correct vision defects. Explain how the strong absorption helps concentrate the energy in a thin layer and thus give greater accuracy in shaping the cornea. Also, explain how this strong absorption limits damage to the lens and retina of the eye.
Police radar determines the speed of motor vehicles using the same Doppler-shift technique employed for ultrasound in medical diagnostics. Beats are produced by mixing the double Doppler-shifted echo with the original frequency. If microwaves are used and a beat frequency of is produced, what is the speed of the vehicle? (Assume the same Doppler-shift formulas are valid with the speed of sound replaced by the speed of light.)
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