What is diffraction grating? Discuss the formation of diffraction patterns due to diffraction grating.
1 Answer
Diffraction Grating: An arrangement of a large number of very narrow equidistant slits is called a diffraction grating. If the slits are parallel to each other then the grating is called plane diffraction grate or plane transmission grating. It can be made by drawing a large number of straight and equidistant parallel lines or scratches over a thin glass plate by means of a fine sharp diamond point. These lines are called rulings which act as opaque and the transparent regions between rulings serve as slits.
If a be the width of the transparent part and b be the width of the opaque portion, then the grating element is, d = a + b = 1 / N; N is the number of lines per unit length.
Theory of Diffraction grating: The figure shows the section of grating, whose slits are perpendicular to the plain paper.
Let,
a = the width of each slit.
b = the distance between two slits (or width of the opaque portion.)
The distance (a + b) is known as a grating element or grating space. If N is the number of lines per inch of the grating then,
\(\left(a+b\right)=\frac{1\;inch}N=\frac{2.54}N\) cm
\(\Rightarrow\left(a+b\right)\sin\left(\theta\right)=n\lambda\)
Where n can take any integral value like 1, 2, 3, 4, 5,...
If n = 0, the central maxima is formed.