Chapter 31: Problem 28
How long does it take light to travel from the Moon to the Earth? From the Sun to the Earth? From Jupiter to the Earth?
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Chapter 31: Problem 28
How long does it take light to travel from the Moon to the Earth? From the Sun to the Earth? From Jupiter to the Earth?
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Two polarizing filters are crossed at \(90^{\circ}\), so when light is shined from behind the pair of filters, no light passes through. A third filter is inserted between the two, initially aligned with one of them. Describe what happens as the intermediate filter is rotated through an angle of \(360^{\circ} .\)
The most intense beam of light that can propagate through dry air must have an electric field whose maximum amplitude is no greater than the breakdown value for air: \(E_{\max }^{\operatorname{air}}=3.0 \cdot 10^{6} \mathrm{~V} / \mathrm{m},\) assuming that this value is unaffected by the frequency of the wave. a) Calculate the maximum amplitude the magnetic field of this wave can have. b) Calculate the intensity of this wave. c) What happens to a wave more intense than this?
The voltage across a cylindrical conductor of radius \(r\), length \(L\), and resistance \(R\) varies with time. The timevarying voltage causes a time-varying current, \(i\), to flow in the cylinder. Show that the displacement current equals \(\epsilon_{0} \rho d i / d t,\) where \(\rho\) is the resistivity of the conductor.
Calculate the average value of the Poynting vector, \(S_{\text {ave }}\) for an electromagnetic wave having an electric field of amplitude \(100 . \mathrm{V} / \mathrm{m}\) a) What is the average energy density of this wave? b) How large is the amplitude of the magnetic field?
The antenna of a cell phone is a straight rod \(8.0 \mathrm{~cm}\) long. Calculate the operating frequency of the signal from this phone, assuming that the antenna length is \(\frac{1}{4}\) of the wavelength of the signal.
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