Spectrosopy-and-the-Doppler-Effect-Module-2

Module Two

  • Spectroscopy and Doppler Effect

Spectroscopy

  • Definition: The study of the interaction between light and matter.

  • Spectroscope: A device that analyzes light from an object.

    • Process:

      • Light from a source (e.g., a light bulb) passes through a narrow slit.

      • The light is directed through a prism.

      • The prism breaks the white light into a continuous spectrum of visible colors.

Emission Lines

  • Defined as single frequencies emitted by particular atoms.

  • Example: Heated hydrogen gas produces specific emission lines.

  • Analogy: Spectra are comparable to supermarket barcodes as they uniquely identify the type and cost of products (e.g., US $24.00 / $36.50 CAN).

Unique Emission Lines

  • Each element has a unique set of emission lines.

  • Identifying Elements: Emission lines can be utilized to identify various elements and compounds.

Spectra from the Sun

  • Observation: The Sun’s light passed through a spectroscope reveals a nearly continuous spectrum.

  • Absorption Lines:

    • Appear as dark lines in the spectrum, indicating the presence of particular elements.

    • These lines assist astronomers in determining which elements are present in a star.

Formation of Absorption Lines

  • Process:

    • Light from a hot bulb (e.g., the Sun) passes through cooler gas containing elements.

    • The cooler gas absorbs specific wavelengths of light that correspond to its emission lines.

    • Characteristics:

      • Absorption lines and emission lines are similar in nature.

Kirchoff’s Laws

  • Law 1: Any solid, liquid, or dense gas that is sufficiently hot will emit all wavelengths, resulting in a continuous spectrum.

  • Law 2: Low-density hot gases emit bright emission lines, useful for identifying the gases.

  • Law 3: Low-density cool gases absorb wavelengths from a light source, creating absorption lines corresponding to their emission lines.

Doppler Effect

  • Concept: The change in wavelength due to the relative motion of the source and observer.

    • Object Moving Towards Observer:

      • Wavelengths become shorter (bunched up).

      • Emission lines shift toward shorter wavelengths, termed Blue Shift.

    • Object Moving Away From Observer:

      • Wavelengths become longer (spread out).

      • Emission lines shift toward longer wavelengths, termed Red Shift.

Applications of the Doppler Effect

  • Purpose: Measures radial velocity, indicating the speed at which objects move towards or away from us.

  • Significance: Useful for studying various astronomical phenomena, including:

    • The gasses of the Sun.

    • The rotation of planets.

    • Observations indicate most galaxies are redshifted, reflecting that they are moving away from each other, supporting the expanding universe theory.