To observe and map discrete atomic line emission spectra, measure the wavelengths of the visible Balmer series of hydrogen (H_α, H_β, H_γ, H_δ, H_ε, H_ζ) using a calibrated grating spectrometer, test the Bohr-Balmer wavelength relationship, and determine the Rydberg constant R_H. Explore a virtual apparatus, collect readings and analyse a graph.
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Adjust the apparatus, then take a reading.
Readings are generated by an ideal model. The diagram is schematic and is not to scale.
Calculations assume an ideal transmission grating obeying d sin θ = m λ with zero prism curvature, negligible Doppler thermal line broadening, and negligible ambient refractive index variations in laboratory air. Real spectrometers exhibit minor chromatic aberration in collimator lenses, mechanical backlash in the micrometer vernier drum, and a refractive index of air n_air ≈ 1.00028 that causes air wavelengths to be approximately 0.18 nm longer than vacuum wavelengths.
Provides an optical bench with a precision bilateral entrance slit, collimating telescope with achromatic objective, central rotatable circular spectrometer table with replica diffraction grating (600 lines/mm), and viewing telescope with calibrated micrometer reticle graduated in tenths of a nanometer.
Emits intense atomic hydrogen emission radiation produced by electron-impact dissociation and collisional excitation of molecular H₂ gas in a constricted capillary bore under low pressure (~1 mmHg).
Delivers a stable 5,000 V AC/DC excitation potential to strike and sustain a steady glow discharge across the gas tube without filament thermal sputtering.
Provide certified spectroscopic wavelength benchmark lines (sodium yellow doublet at 589.0 nm and 589.6 nm, mercury green line at 546.1 nm) for precise spectrometer reticle zero-offset and dispersion calibration.
Permits comparative study of flame line emission spectra of alkali and alkaline-earth metal chlorides (NaCl, LiCl, SrCl₂, CaCl₂) introduced into a non-luminous gas flame on platinum/nichrome loops.
Measures angular diffraction deviation θ and directly reads optical wavelength λ to 0.1 nm resolution using anti-parallax vernier drum optics.
To observe and map discrete atomic line emission spectra, measure the wavelengths of the visible Balmer series of hydrogen (H_α, H_β, H_γ, H_δ, H_ε, H_ζ) using a calibrated grating spectrometer, test the Bohr-Balmer wavelength relationship, and determine the Rydberg constant R_H. Suggested independent settings: 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 .
Illuminate the entrance slit with an incandescent lamp. Focus the viewing telescope crosshairs sharply on the slit image. Rotate the collimator tube until the slit image is strictly parallel to the vertical reticle hair, and adjust the collimator lens to produce a perfectly parallel incident beam (Schuster’s method). Set the diffraction grating perpendicular to the optical axis on the central turntable.
Collimating the incident light into plane wavefronts ensures that the grating equation d sin θ = m λ holds rigorously without spherical aberration.
Place the sodium vapor lamp in front of the entrance slit. Locate the intense first-order yellow emission lines. Align the reticle crosshair on the resolved sodium doublet (D₁ = 589.6 nm, D₂ = 589.0 nm) and calibrate the spectrometer drum index. Verify the calibration against the mercury 546.1 nm green line to confirm linear dispersion across the focal plane.
Establishing a certified reference benchmark eliminates spectrometer zero-point index error and guarantees absolute wavelength accuracy.
Mount the hydrogen Geissler tube directly in front of the entrance slit within a protective shielded housing. Energize the high-voltage supply to initiate the pink-purple glow discharge. Observe the spectrum through the telescope and identify the four brilliant visible Balmer lines against the faint molecular background band.
Constricting the discharge inside the capillary bore maximizes the current density and enhances atomic emission relative to molecular continuous bands.
Rotate the telescope slowly toward the red region and bisect the vivid ruby-red H_α line (n = 3 → 2) with the crosshairs. Read and record its wavelength λ = 656.3 nm. Progressively measure the cyan H_β line (n = 4 → 2 at 486.1 nm), the blue-violet H_γ line (n = 5 → 2 at 434.0 nm), the deep violet H_δ line (n = 6 → 2 at 410.2 nm), and the near-ultraviolet limits H_ε (n = 7 → 2 at 397.0 nm) and H_ζ (n = 8 → 2 at 388.9 nm).
Sampling six consecutive Balmer transitions spanning n = 3 through n = 8 provides extensive leverage for linear regression testing of the Rydberg formula.
Introduce platinum wires wetted with sodium chloride (yellow 589 nm), lithium chloride (crimson 671 nm), and strontium chloride (red 680 nm, blue 461 nm) into a non-luminous Bunsen flame. Record the characteristic flame line positions. Direct solar light through the slit using an exterior heliostat mirror to observe the dark Fraunhofer absorption lines (C, D, F, G) matching the hydrogen and sodium emission wavelengths.
Comparing atomic flame emission with solar absorption directly demonstrates Kirchhoff’s law of radiation and proves the presence of terrestrial elements in stellar atmospheres.
For each spectral line n, compute the Bohr quantum geometric factor x = 1/4 − 1/n² and the optical wavenumber y = ν̃ = 1 / λ (in m⁻¹). Plot ν̃ on the vertical axis against (1/4 − 1/n²) on the horizontal axis. Compute ordinary least-squares linear regression to determine the slope S = R_H (in m⁻¹) and the vertical intercept b. Compare the measured Rydberg constant against the standard CODATA value (1.0967758 × 10⁷ m⁻¹).
Linear regression over all six Balmer transitions averages out spectrometer drum reading quantization and tests the inverse-square quantum energy level structure of the Bohr atom.
Points are your observations. The fit uses SI x and y values before display scaling.
| # | Upper energy level quantum number n () | Spectral emission wavelength λ (nm) | Bohr level factor (1/4 − 1/n²) | Wavenumber ν̃ = 1/λ (m⁻¹) | Remove |
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