Question: What is diffraction grating and grating element? Explain the experimental method to determine the wavelength of the spectral line using diffraction grating?
0

Topic: Diffraction grating and grating element

Difficulty: Medium

Marks: 7M

mumbai university ap2 • 604 views
ADD COMMENTlink
modified 8 months ago by gravatar for Yashbeer Yashbeer170 written 10 months ago by gravatar for vermavarsha432 vermavarsha4320
0

Diffraction grating:

A diffraction grating is an arrangement consisting of a large number of parallel slits of same width and separated by equal opaque spacing. It is obtained by ruling equidistant parallel lines on a glass plate with the help of a fine diamond point.

Grating element:

Let N be the number of parallel slits, each of width 'a' and separated by opaque space 'b'. Then, the distance between the centers of the adjacent slits is $d = a + b$ and is known as grating element.

Determination of wavelength of the spectral line using diffraction grating:

The diffraction grating is often used in the Lab for the determination of wavelength of light. The grating spectrum of the given source of monochromatic light is obtained by using a spectrometer as shown -

enter image description here

Symmetrical diffraction pattern consisting of different orders can be seen. The angle of diffraction $\theta$ for a particular order 'm' of the spectrum is measured.

The number of lines per inch of grating are written over it by the manufacturer. Hence the grating element is

$$ a + b = \frac{1}{ \text{No. of Lines / cm}} = \frac{2.54}{ \text{No. of Lines / inch} } $$

Thus, using equation $(a + b) sin \theta = m \lambda$

The unknown wavelength $'\lambda'$ of the spectral line can be calculated by putting the value of the grating element (a+b), the order 'm' and the angle of diffraction $'\theta'$

ADD COMMENTlink
modified 8 months ago by gravatar for Yashbeer Yashbeer170 written 8 months ago by gravatar for Ankit Pandey Ankit Pandey100
Please log in to add an answer.