Chapter 36: Problem 19
Calculate the peak wavelengths of a) the solar light received by Earth, and b) the light emitted by the Earth. Assume that the surface temperatures of the Sun and the Earth are \(5800 .\) K and \(300 . K\), respectively.
Chapter 36: Problem 19
Calculate the peak wavelengths of a) the solar light received by Earth, and b) the light emitted by the Earth. Assume that the surface temperatures of the Sun and the Earth are \(5800 .\) K and \(300 . K\), respectively.
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Get started for freeA pure, defect-free, semiconductor material will absorb the electromagnetic radiation incident on it only if the energy of the individual photons in the incident beam is larger than a threshold value known as the band-gap of the semiconductor. Otherwise, the material will be transparent to the photons. The known room-temperature band-gaps for germanium, silicon, and gallium-arsenide, three widely used semiconductors, are \(0.66 \mathrm{eV}\) \(1.12 \mathrm{eV},\) and \(1.42 \mathrm{eV},\) respectively. a) Determine the room-temperature transparency range of each semiconductor. b) Compare these with the transparency range of \(\mathrm{ZnSe},\) a semiconductor with a band-gap of \(2.67 \mathrm{eV}\), and explain the yellow color observed experimentally for the ZnSe crystals. c) Which of these materials could be used to detect the \(1550-\mathrm{nm}\) optical communications wavelength?
Electrons having a narrow range of kinetic energies are impinging on a double slit, with separation \(D\) between the slits. The electrons form an interference pattern on a phosphorescent screen, with a separation \(\Delta x\) between the fringes. If the spacing between the slits is reduced to \(D / 2,\) the separation between the fringes will be a) \(\Delta x\) c) \(\Delta x / 2\). b) \(2 \Delta x\). d) none of these.
A nitrogen molecule of mass \(m=4.648 \cdot 10^{-26} \mathrm{~kg}\) has a speed of \(300.0 \mathrm{~m} / \mathrm{s}\) a) Determine its de Broglie wavelength. b) How far apart are the double slits if a beam of nitrogen molecules creates an interference pattern with fringes \(0.30 \mathrm{~cm}\) apart on a screen \(70.0 \mathrm{~cm}\) in front of the slits?
Now consider de Broglie waves for a (relativistic) particle of mass \(m,\) momentum \(p=m v \gamma,\) and total energy \(E=m c^{2} \gamma,\) with \(\gamma=\left[1-(w / c)^{2}\right]^{-1 / 2}\) The waves have wavelength \(\lambda=h / p\) and frequency \(f=E / h\) as in Problem \(36.45,\) but with the relativistic momentum and energy values. a) For these waves, calculate the dispersion relation, \(\omega=\omega(\kappa),\) where \(\kappa\) is the wave number. b) Calculate the phase velocity \(\left(v_{p}=\omega / \kappa\right)\) and the group velocity \(\left(v_{k}=\partial \omega / \partial \kappa\right)\) of these waves. c) Which corresponds to the classical velocity of the particle?
Consider an electron whose de Broglie wavelength is equal to the wavelength of green light (550 nm). a) Treating the electron non relativistically what is its speed? b) Does your calculation confirm that a non relativistic treatment is sufficient? c) Calculate the kinetic energy of the electron in electron-volts.
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