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Diffraction grating

1) If a diffraction grating has 6,000 grooves per centimeter, to what angle will the first order constructive interference "line" of the Hydrogen Alpha (red) emission be diffracted?

2) Atoms of the hydrogen gas enveloping a particular star absorb the Hydrogen Alpha wavelength from the white light emanating from the surface of the star and reemit that color in random directions, causing the spectrum received by observers on Earth to have a dark line due to the missing light. (Discovered by Joseph Fraunhoffer) Suppose the measured wavelength of the dark line is found to be 6555 Angstroms. Is the radial motion of the star toward or away from Earth? Compute how fast the star is moving relative to the earth.

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1) For single-line sources, the constructive interference fringes of a diffraction grating are given by d*sin(theta) = m(lambda)
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<br>d is the distance between pairs of grooves. Here, we have 6000 grooves per centimeter, or 5999 spaces between grooves, giving
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<br>d = 1/5999 cm
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<br>Lambda is the wavelength of ...

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