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St. Mary's H.S. Physics Online

 

Background

Electrons give off light when they return to the ground state after being excited by an energy source

 

 

Bohr studies the light given
off by a 'Black Body'

 

 

Neils Bohr, right

 

 

'Black Body' = heated body that gives off only the light from its internal glow - no reflected light

 


Material was heated and the light
 given off was analyzed

 

 

 

 

Spectroscopy

School blocks YouTube? Click below

| Onsite Version |

St. Mary's U. Astronomy and Physics Dept.

 


Spectral lines
Physics 2000

Emission Spectra

 

Whatever colors an element gives off, it also .....

 

 

 

 

 

 

... absorbs

 

Atomic Spectra
University of Oregon 

 

Atomic Spectra for Iron

 

 

Full Spectrum

 

Hydrogen Emission
/Absorption Spectrum

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Place your mouse over the image to see the absorption spectra

 

 

Full Spectrum

 

 

Helium

 Emission/Absorption 
Spectrum

Place your mouse over the image
to see the absorption spectra

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Every Energy level transition creates a single spectral line

 

 

| Onsite Version |

 

 

 

"Science of the Silicon Solar Cell"

Don Ion

 

 

How many different spectral lines can be produced
by an atom with 5 energy levels?

 

 

 

Answer

 

   

 

 

 

10 Spectral Lines

 

 

10 colors

 

 

10 frequencies

10 photons

 

 

 

 

 

Black Body Radiation Results:

 

1. Only the high energy objects gave off colors on the violet side of the spectrum 

 

 

 

R O Y

G

B

V


Low Frequency

 

High Frequency

 

Frequency related to Energy

 

 

 

2. Electrons in atoms are not capable of giving off all colors (energies)

 

 

 

3. Each element gives off a unique pattern of colors called a 'bright line spectrum'.

 

 

  This knowledge is very useful to chemists and other scientists. Why?

 

 

 

Answer

 1. Spectral lines used to:

 

  • identify unknown elements.

 

  • determine the composition of distant stars

 

 

 

 

 

 

To Identify an Unknown Element

 

 

- Electrify, Heat it up and analyze its colors.

 

- Compare emitted colors to a database of elemental spectral lines

 

 

 

 

 

 

 

The diagram below represents the bright-line spectra of four elements, A, B, C, and D, and the spectrum of an unknown gaseous sample.

Based on comparisons of these spectra,
which two elements are found
in the unknown sample?

Jan 2006

 

 

 

B and C

 

What are stars made of ?

 

 

 

 

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