![]() ![]() In 1907 the British physicist Ernest Rutherford (1871–1937) New Zealand–Canada–England showed that alpha particles are the nuclei of helium atoms. The gas was first isolated from terrestrial sources in 1895 by the British chemist William Ramsay, who discovered it in cleveite, a uranium-bearing mineral. Shortly afterward it was identified as an element and named by the British chemist Edward Frankland and the British astronomer Joseph Norman Lockyer. The French astronomer Pierre Janssen (1824-1907) discovered helium in the spectrum of the corona of the Sun during an eclipse in 1868.Norman Lockyear in the spectrum of a solar eclipse. Two German scientists, Robert Bunsen (a chemist) and Gustav Kirchhoff (a physicist), showed that the dark lines in the spectrum of sunlight corresponded to the bright lines of excited elements seen in laboratories on the Earth.A shadow is a region behind an obstacle into which a wave does not easily diffract. is most apparent when the size of the obstacle or opening ( a) and the wavelength of the wave ( ) are of the same order ( a ). These spectral lines are wider since they came from a wider source. is the bending or spreading of a wave around an obstacle or through an opening. The discrete spectrum of a fluorescent light. The discrete spectrum of excited helium gas The discrete spectrum of excited mercury vapor Lastly, we plug in our given values and solve. The light intensity is maximum at q zero degrees, and decreases to a minimum (where the intensity is zero) at angles dictated by the equation above. Next, we rearrange the equation to solve for wavelength. Laser light through a diffraction grating.Ĭontinuous: temperature from Wien's Displacement Law We can start with our equation that relates frequency, wavelength, and the speed of light. Multiple source interference (diffraction grating) single source interference (self interference) ![]() Laser light through two closely spaced slits. animate at your own riskĭouble source interference. Do not click on the animations if you have photosensitive epilepsy or a similar condition. The sources are closer together in the image on the right. (The interference fringes will be dealt with later in this section.) This image sequence is also available as an animated gif. Note that as the opening gets narrower, the amount of diffraction in the horizontal direction increases. Why is it possible to hear around corners, but not see around them? Diffraction of laser light through a vertical opening of decreasing width. Diffraction is the bending or spreading of light through an opening or around an obstacle. ![]()
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