(455) Emission and absorption spectra [IB Physics SL/HL]

Emission and Absorption Spectrum

Basics

• Emission and absorption spectroscopy reveals properties of atoms.

• Excited atoms emit photons when electrons drop to lower energy levels.

Energy Levels

• Electrons can be excited by applying energy (e.g., electric potential).

• Electrons rise to higher energy levels and release energy as photons when returning to lower levels (E=HF).

• Unique energy differences correspond to different photon colors.

Emission Spectrum

• Emission spectra are produced when electrons transition between energy levels, emitting specific photons.

• Each element emits a unique pattern of light, indicative of its atomic structure (discrete energy levels).

• Quantized Energy Levels: Electrons occupy specific energy levels and cannot exist between them.

Example: Hydrogen Emission Spectrum

• Hydrogen displays distinct wavelengths in its emission spectrum (e.g., 656 nm, providing a reddish hue).

• Each element, like sodium, has identifiable lines in its spectrum, acting as a fingerprint.

Absorption Spectrum

• Absorption occurs when a gas absorbs photons matching its energy levels, leaving black lines in a continuous spectrum.

• Emission lines appear as bright lines on a black background; absorption lines appear as black lines on a bright background.

Chemical Composition Insights

• Unique emission/absorption patterns reveal the chemical composition of unknown gases.

• Astronomical observations (e.g., from stars) utilize these spectra to determine stellar compositions without direct sampling.

Redshift Phenomenon

• Observed lines can be shifted due to the Doppler effect, indicating movement relative to the observer (e.g., redshift implies an object is moving away).

Application in Astronomy

• Spectral analysis helps categorize stars and understand their compositions and movements.

• Redshift measurements aid in universe expansion studies and the detection of distant celestial objects.

Exoplanet Detection

• Transits of exoplanets in front of stars allow for spectral analysis of light altered by planetary atmospheres.

• The James Webb Space Telescope analyzes spectra to detect elements like oxygen and carbon dioxide, hinting at potential life.