Light from a helium-neon laser is used to illuminate two narrow slits. The interference pattern is observed on a screen behind the slits. Twelve bright fringes are seen, spanning a distance of . What is the spacing (in mm) between the slits?
The Spacing distance between the two slits is.
Helium-neon (He-Ne) lasers are often used for interferometry because they are inexpensive and produce a consistent, visible output. They generally work at a wavelength of , however customized versions with useable outputs at other visible and infrared wavelengths are also available.
The distance between two adjacent fringes is calculated as follows:
is the distance between two subsequent slits, and is the distance between two successive slits.
We have bright fringes in this problem, which means there are spaces between them. If , the distance between successive brilliant fringes is calculated as follows:
When we combine the two equations for , we get
This results in,
We get numerical values and return them.
One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. Having recently studied optics in your physics class, you're not too surprised to see that the patch of light seems to be a circular diffraction pattern. It appears that the central maximum is about across, and you estimate that the distance from the window shade to the wall is about . Estimate (a) the average wavelength of the sunlight (in ) and (b) the diameter of the pinhole (in ).
A Michelson interferometer uses light from a sodium lamp. Sodium atoms emit light having wavelengths and . The interferometer is initially set up with both arms of equal length , producing a bright spot at the center of the interference pattern. How far must mirror be moved so that one wavelength has produced one more new maximum than the other wavelength?
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