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Definition of diffraction: The wave nature of light is more recognized by incidence of diffraction. The word diffraction is resulting from Latin

word diffractus which refers to split to pieces. When waves meet barrier, they bend round boundaries of harms if

dimensions of the barriers are equal to the wavelength of the waves. The perversion of waves more or less the

boundaries of an obstacle is known as diffraction.

From the above definition we can understand the concept of diffraction.

Overview of Diffraction:Below figure shows passage of waves via an opening. When the opening is big evaluated to a wavelength,

the waves do not twist round the boundaries. When the opening is little, the twisting effect round the boundaries is

noticeable. When the opening is very little, the waves spread over the entire surface behind the opening. The opening

seems to act as an independent source of waves, which propagate in all sides after the opening.

Figure(a)- plane wave does not twist at the cut if the opening d figure(b) - twisting is noticeable when d figure(c) -

twisting taken place to such an extent that light can be professed in way normal to ray propagation, telling that

opening acts as peak source, when >d.

Types of Diffraction:There are two types of diffraction is available. They are,

Fresnel diffraction

Fraunhofer diffraction

Definition of Fresnel diffraction:

Fresnel diffraction is that in which either peak basis or screen or both are at limited distances from obstacle. It

concerned with non-plane wave fronts.

Definition Fraunhofer diffraction:

Fraunhofer diffraction is that in which basis and screen are successfully at unlimited distances from obstacle. It

concerned with similar rays and plane wavefronts.

From the above definition we can understand the types of diffraction.

Application of Diffraction:

Wavelength of X-rays can be established by X- ray diffractometer.

Using diffraction rasping, the wavelength of monochromatic or compound radiation can be established.

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The structural morphology of the crystal can be established.

Ultra sound scanning which is used to discover tumors, ulcers in human body can be diagnosed by this

phenomenon.

Velocity of sound in liquids can be projected with the help of diffraction procedures.

Diffraction in sound waves and radio waves are readings observed as they have a relatively longer

wavelength compared to light waves.

In the above figure l

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Each point on the unblocked portion of plane wavefront AB sends out secondary wavelets in all directions.

The waves from points equidistant from the center C lying on the upper and lower half reach the point O with

path difference being zero and hence reinforce each other producing a maximum intensity at the point 0.

Consider a point 'P' on the screen. The intensity at P will depend on the path difference between the

secondary waves emitted from the corresponding point of the wavefront. Consider a set of waves making

an angle q with CO. Draw AN perpendicular to BK. The path difference between the secondary waves

reaching P from

A and B = BN = AB Sin q = a sin q

where AB = a width of the aperture.

If BN = a (i.e., path difference) the whole wave front can be considered to be divided into two halves, i.e., CA

and CB. The path difference between A and C will be l/2 and so for every point in the upper half AC, there is

a corresponding point in the lower half CB for which the path difference between the waves is l/2. So P is a

point of destructive interference.

qn is the angle of diffraction of nth dark fringe from O.

If

Note on diffraction: Diffraction occurs due to interference of two wave trains coming from two different points of the same

wavefront and so a special case of interference occurs. Also the width and intensities of fringes in a

diffraction is different and not equally bright. In interference, width and intensities of fringes are all equal.

Introduction to Diffraction Gratings:

Grating is a device used to find the diffraction of light. The propertyof bending of light rays at the edges of an obstacle or slit is calledDIFFRACTION . To observe the diffraction pattern the necessary condition is thatthe size of the aperture must be approximately equal to the wavelength of light.

Grating consists of a large number of parallel slits separated by opaquedistances. The width of each slit is approximately equal to wavelength of light.Basically there are two types of gratings, namely transmission grating andreflection grating.

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Transmission grating can be prepared by drawing a large number of parallel linesusing a diamond point, on a transparent medium. The line drawn acts as opaqueto light and the distance between each line is transparent to light.

Reflection grating can be prepared by drawing a large number of parallel lines

using a diamond point, on an opaque medium. The line drawn acts astransparent to light and the distance between each line is opaque to light.

Experiment on Diffraction Gratings When a white light incidents on a DIFFRACTION GRATING, light is diffracted in

various direction at various angles. Diffraction pattern consists of spectra of various colors in different orders. If 'e' is the width of the slid and 'd' is thedistance between the slits then the equation which explains the grating spectra is

(e+d) sin = n ................... (1)

Here 'n' is represents the order of the spectrum and

'' is the wavelength of light or color.