Physics (From diffraction)

                            Diffraction

MISSING ORDER

When condition for maximum intensity in interference ( double slit) and the condition for minimum intensity in diffraction ( single slit) are simultaneously satisfied then those orders are missing from the spectrum known as missing order.

Condition for maximum intensity in diffraction (single slit)

Question: Deduce the missing order for a double slit Fraunhofer diffraction, the slit width e= 0.16mm and they are 0.8 mm apart.

Ans: m/n= (0.16+0.8)/0.16= 0.96/0.16

m/n= 6

m= 6n

Question: What particular spectra would be absent if the transparencies and the opacities of the grating are equal?

Ans:a=e(given)

(e+a)/e= m/n

2e/e=m/n

m=2n

Since, n= 1;2;3;.....

m= 2;4;6;.......

N-Slit Diffraction Fraunhofer Diffraction by N-slits(grating)

Grating- A grating in an arrangement of N number of parallel slits of same width which are seperated by opaque slits.

When the light incident on the grating then it is diffracted from each slits.

These beams are converged at a point P on the screen by means of a converging lens 'L'.

We know resultant amplitude of a single slit.

Resolving Power: Ability of an optical instrument to view clear image of an object.

Optical instrument have circular apparatus that produce a diffraction pattern instead of a sharp image.

The ability an optical instrument to just resolve the image of two closely spaced objects is called it's resolving Power.

Rayleigh's Criterion of Resolution

Sodium lamp gives light of two wavelength

Resolving Power

Principle maxima of first concide with first minima of second.

When two closey spaced point sources of wavelength are said to be just resolved by an optical instrument if the principle maximum in the diffraction pattern of one wavelength coincide with the just minimum in the diffraction pattern of one wavelength coincide  with the  first minimum in the diffraction pattern of the other. Then their is follows Rayleigh's Criterion for resolution.

Resolving Power of grating

It is defined as the ratio of wavelength of a line to the wavelength difference with th line which is seen to be just seperated from the first line.