It also underlies the phenomena of single-slit diffraction and double-slit interference of light which is an electromagnetic wave to be observed in this experiment.
If the screen is placed at distance L from the slit, alternating bright and dark fringes at different positions of y each fringe will run parallel to the slit are observed, as schematically shown in Figure 1b left. The narrow slits will still produce diffraction patterns, but usually the slit width a is much smaller than the separation d , and the intensity modulation due to the diffraction pattern will superimpose on the much closer and equally spaced double-slit interference fringes.
Since a laser is the best approximation for this kind of ideal light source, a laser beam is used as the light source in this experiment historically in the pre-laser time, such experiments have used a point-like light source such as that produced by passing light though a small hole.
On the other hand, the positions and spacing of the fringes are usually well-predicted by the simple model discussed above. Figure 1: Single slit diffraction. Figure 2: Double slit interference. Subscription Required. Please recommend JoVE to your librarian. Interference and diffraction are characteristic phenomena of all waves, from water waves to electromagnetic waves such as light.
Interference refers to the phenomenon where two waves of the same kind overlap to produce a resultant wave of greater, lower, or the same amplitude. Diffraction is defined as the bending of a wave around the corners of an obstacle or aperture.
In this case, differential parts of the wave can interfere and give rise to a spatial alternation of large and small amplitude. This video will demonstrate the wave nature of light by observing diffraction and interference patterns. Different parts of waves can overlap and "interfere" to produce a spatial alternation of strong and weak wave amplitudes, called an interference pattern. When the amplitudes of the interfering waves add up, it is called constructive interference; whereas, when their amplitudes subtract from each other, it is called destructive interference.
Now, if light of wavelength lamda, is shone on a single narrow slit, the intensity far away from the slit alternates between large and small or nearly zero values, corresponding to "bright" and "dark" regions, also known as "fringes". The center of this pattern is always bright, along the y-axis of the slit.
This alternation is known as the "diffraction pattern" of the light through a small aperture. It is a characteristic phenomenon for waves. Specifically, points between the two edges of the aperture "re-emit", or in other words "diffract" the light wave towards different directions.
Interference between different parts of the diffracted light waves results in the formation of the diffraction pattern. In the case of two closely spaced slits, the pattern formed, famously known as the "Young's double-slit interference pattern", is due to the interference of the diffracted light from both slits. The following protocol demonstrates how to setup the single-slit and double-slit experiments and interpret their results.
Using a pair of scissors cut the aluminum foil into two approximately 2-inch by 2-inch square pieces. Also, cut the cardboard into two approximately 3-inch by 3-inch square pieces with a hole of about 1-inch diameter in the center. Next, take one piece of aluminum foil, and using a razor blade, cut a straight slit about 1 centimeter long in the middle of the foil. Tape the foil onto one cardboard with the slit positioned inside the hole. Now, tape one edge of the cardboard to the wooden block and slide the white wall about 30 centimeters away from the slit.
Make sure that the cardboard is perpendicular to the table surface, and the hole and vertical slit are exposed, and facing the wall. Place the laser pointer on the other side of the mounted cardboard, while ensuring that the laser beam will be parallel to the table.
Now wear the laser safety goggles, turn on the laser pointer, and shine the laser beam onto the slit. Turn off the room light, and observe the light pattern on the wall on the other side of the foil. Turn OFF the laser pointer and remove the laser safety goggles. Next, stack three razor blades such that the middle blade is recessed. Take the other aluminum foil and using the stack of razor blades and a ruler cut two closely spaced straight parallel slits, about 1 centimeter long in the middle of the foil.
If the difference between the phases is intermediate between these two extremes, then the magnitude of the displacement of the summed waves lies between the minimum and maximum values.
Consider, for example, what happens when two identical stones are dropped into a still pool of water at different locations. Each stone generates a circular wave propagating outwards from the point where the stone was dropped. When the two waves overlap, the net displacement at a particular point is the sum of the displacements of the individual waves.
At some points, these will be in phase and will produce a maximum displacement. In other places, the waves will be in anti-phase and there will be no net displacement at these points.
Thus, parts of the surface will be stationary. Diffraction refers to various phenomena that occur when a wave encounters an obstacle. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects occur when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance.
Crest again meets crest. The diagram on the right shows the geometry for the fringe pattern. These angles are found by applying the condition for constructive interference, which is. The distances from the two slits to the screen differ by an integer number of wavelengths.
Crest meets crest. The angles at which dark fringes occur can be found be applying the condition for destructive interference, which is.
Crest meets trough. Link: Physics Wave Interference. The figure on the right shows the interference pattern for various numbers of slits. The width of all slits is 50 micrometers and the spacing between all slits is micrometers. The location of the maxima for two slits is also the location of the maxima for multiple slits. The single slit pattern acts as an envelope for the multiple slit patterns.
Diffraction gratings contain a large number of parallel, closely spaced slits or grooves. We cannot use the small angle approximation for relating wavelength and the position of the maxima on a screen for gratings, but have to use. Diffraction gratings disperse white light into its component colors because different wavelengths produce bright fringes at different angles. The spectral pattern is repeated on either side of the main pattern. These repetitions are called "higher order spectra".
There are often many of them, each one fainter than the previous one. The first order bright line appears 0. The distance between the slits is 0. Now compare with the relationships above. Diffraction Diffraction occurs when a wave: passes an edge passes through a narrow gap goes past an object None of the properties of a wave are changed by diffraction. Reveal answer up. Higher Subjects Higher Subjects up.
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