Home 2nd Year Physics Notes Class 12 Physics Chapter 20 Notes- Atomic Spectra

Class 12 Physics Chapter 20 Notes- Atomic Spectra


In this post, I am sharing the Class 12 Physics Chapter 20 Notes PDF for the students of Intermediate Part 2. This chapter’s name is Atomic Spectra. Students can download the Class 12 Physics Chapter 20 Notes PDF on their laptops or mobile. These Physics Notes are for all the boards working under the Punjab Board like Gujranwala Board, Lahore Board, Faisalabad Board, Multan Board, Rawalpindi Board, Sargodha Board, DG Kahn Board, and Sahiwal Board. Here are the complete FSC 2nd Year Physics Notes PDF chapters.

FSC Part 2 Physics Chapter 20 Notes – Atomic Spectra

Class 12 Physics Notes

Define Spectroscopy?

The branch of physics which deals with the investigation of wavelengths and intensities of electromanetic radiations emitted or absorved by atoms. There are three types

(i) Continuous Spectra

(ii) Band Spectra

(iii) Line Specctra of discrete spectra

(i) Continuous Spectra

The electromagnetic radiation emitted by the black body is an example of continuos spectra.

(ii) Band Spectra

The molecular spectra are the example of band spectra.

(iii) Line Specctra of discrete spectra

The atomic spectra are the example of line sectra.

What is atomic spectrum/spectra?

When an atomic gas or vapor at much less than atmospheric pressure is suitably excited, usually by passing an electric current through it, the emitted radiation has a spectrum, which contains certain specific wavelengths only. An idealized arrangement for observing such atomic spectra is shown in the figure. An actual spectrometer uses diffraction grating for better results. The impression on the screen is in the form of lines if the slit in front of the source S is a narrow rectangle. It is for this reason that the spectrum is referred to as the line spectrum. The fact that the spectrum of any element contains wavelengths that exhibit definite regularities was utilized in the second half of the 19th century in identifying different elements.

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