A laser is directed at a double-slit arrangement. If we increase the wavelength

Question

A laser is directed at a double-slit arrangement. If we increase the wavelength of the light, which of the following will occur to the pattern on a distant screen? The spacing between the interference fringes will decrease, but the width of the overall diffraction envelope will increase. The spacing between the interference fringes will increase, but the width of the overall diffraction envelope will decrease. Both the spacing between the interference fringes and the width of the overall diffraction envelope will increase. Considering larger objects, a skyscraper has two tall antennae separated by 3 meters. Each antenna has one blue and one red light. You can resolve the two blue lights but not the red ones. Assume that your pupils have a diameter = 2 mm at night, and that blue lights wavelength is 475 nm, while red light's wavelength is 650 nm. Approximately how far are you from the skyscraper? (Also assume that you have perfect vision' limited only by diffraction.)

Explanation / Answer

We have a equation,

y = L/d

Where y = spacing between fringes , L = distance of screen from the diffraction grating, d= width of diffraction grating.

It shows if increases y increases.

Increases in y leads to increase in the width of the envelope.

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