Spectroscope

A Description

Using the spectroscope

Taking readings

Calibrating the spectroscope

Return to
Main Menu

A Description

A spectroscope contains a diffraction grating that separates electromagnetic radiation into its component wavelengths. The spectroscope can be used to measure absorption or emission spectra.

Using the spectroscope

When using a spectroscope, eliminate as much external light as possible so that the only light entering the instrument is due to the light sourcebeing examined. If the source is a gas emission tube, DO NOT TOUCH it! Gas emission tubes operate at high voltages and will cause electric shocks if touched.

Video: DO NOT touch the emission tube! ( 586K )

To view a spectrum, the light slit must be aligned correctly.

Video: Proper alignment of slit ( 1.97 M ) Text description

When the slit is properly aligned, examine the spectrum through the spectroscope.

Video: Examining the spectrum ( 3.83 M )

When recording several spectra, take all measurements at approximately the same angle and distance from each light source.

The white lines on the spectroscopes indicate the positions of the light slits.

The student using the spectroscope on the left sees a red line at 615 nm, while the student using the spectroscope on the right sees the red line at 630 nm. Explain this discrepancy. Who obtained a more correct reading? Answer

Taking readings

The spectrum is displayed on a wavelength scale inside the spectroscope, to the right of the slit. The numbers on the scale mark hundreds of nanometers, and the thick dashed lines are 50 nanometer increments. Each thin solid line on the scale represents 10 nanometers.

When measuring an emission spectrum, record the wavelengths and colors of the individual lines.

Because of the thickness of the emission lines, readings should be estimated to the nearest five nanometers.

An emission spectrum with a blue line at about 445 nm, a green line at 525 nm, and a red line at 635 nm.

When measuring an absorption spectrum, record the ranges of wavelengths for which no light is visible.

An absorption spectrum with absorptions at 460 - 470 nm, 550 - 556 nm, 557 - 559 nm, and 605 - 610 nm.

Calibrating the spectroscope

Readings obtained from a hand-held spectroscope may not correlate precisely with known values measured with more sophisticated instruments. Therefore, calibrating the spectroscope is necessary.

First, obtain a set of known emissions for a gas. Then, using a gas emission tube containing that gas, record the wavelengths observed using a spectroscope. Make a graph of known wavelengths versus observed wavelengths. This plot can now be used to calibrate other readings from the spectroscope. Show me an example

Miscellaneous Exercises

Which of the following could be true about the solution shown below?

A. It is absorbing orange light.

B. It is transmitting orange light.

C. It transmits all colors of light except orange.

D. It absorbs all colors of light except orange.

Answer

Given the following plot of absorbance vs. wavelength as obtained using a Spectronic 20™, sketch the expected absorption spectrum that would be seen through a hand-held spectroscope for this species.

Spectroscope

A Description

Using the spectroscope

Taking readings

Calibrating the spectroscope

A spectroscope contains a diffraction grating that separates electromagnetic radiation into its component wavelengths. The spectroscope can be used to measure absorption or emission spectra.

To view a spectrum, the light slit must be aligned correctly.

When the slit is properly aligned, examine the spectrum through the spectroscope.

When recording several spectra, take all measurements at approximately the same angle and distance from each light source.

The student using the spectroscope on the left sees a red line at 615 nm, while the student using the spectroscope on the right sees the red line at 630 nm. Explain this discrepancy. Who obtained a more correct reading? Answer

The spectrum is displayed on a wavelength scale inside the spectroscope, to the right of the slit. The numbers on the scale mark hundreds of nanometers, and the thick dashed lines are 50 nanometer increments. Each thin solid line on the scale represents 10 nanometers.

When measuring an emission spectrum, record the wavelengths and colors of the individual lines.

Because of the thickness of the emission lines, readings should be estimated to the nearest five nanometers.

When measuring an absorption spectrum, record the ranges of wavelengths for which no light is visible.

Readings obtained from a hand-held spectroscope may not correlate precisely with known values measured with more sophisticated instruments. Therefore, calibrating the spectroscope is necessary.

Miscellaneous Exercises

Which of the following could be true about the solution shown below?

A. It is absorbing orange light.

B. It is transmitting orange light.

C. It transmits all colors of light except orange.

D. It absorbs all colors of light except orange.

Answer

Given the following plot of absorbance vs. wavelength as obtained using a Spectronic 20™, sketch the expected absorption spectrum that would be seen through a hand-held spectroscope for this species.

Answer

Given the following list of known emissions (wavelengths in nm), identify the gas responsible for the emission spectrum shown below.

Radon: 745, 705

Argon: 707, 696

Krypton: 587, 557

Xenon: 467, 462, 450

Answer

Related modules: Spectronic 20™ at Variable Wavelength