Activity 1(teacher demo)

• Aim the beam from a red laser pointer at a wall
• Pass the beam through a diffraction grating
• Compare results for green laser pointer vs. red laser pointer.

Activity 1: Interpreting Results

• We can use some kind of LENGTH measurement to “measure” color
• Which color spreads out more? Red or Green
• If we tried different colors, the trend in extent of spreading follows the sequence of colors in a rainbow (ROYGBV, “Red, Orange, Green, ...)
• Will violet laser beam spread out more than green?

Activity 1: Explanation

• Light is made up of electromagnetic waves (EM waves)
• A wave is periodic disturbance that transports energy from one location to another.
• Periodic means it follows a repeating pattern.
• Wavelength (λ) – distance over which a pattern is completed
• EM Waves with λ from 400-800 nm are visible to humans. The color we see depends on λ

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Activity 1: Explanation

• When a wave encounters obstacles, it bends. Phenomenon is called diffraction.
• Waves bent from different locations “interfere” when they meet.
• Where light waves are in sync, we say that there is constructively interference 🡺 bright spots.
• Where light waves are out of sync, we say that there is destructive interference 🡪 dark spots.

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Activity 1: Explanation

• Which figure below illustrates destructive interference?

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Activity 1: Explanation

Activity 1: Explanation

Activity 2 (teacher-led expt)

Activity 2 - Explanation

Activity 3 (follow the teacher)

• Use Excel to calculate wavelength of red laser pointer from the data
• Template 🡪
• Enter formulas�in the highlighted�cells

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Activity 4 (teacher demo)

• Use Vernier Spectrovis spectrophotometer and fiber optic cable to measure wavelength of red laser pointer
• Fiber optic cable guides light to the detector

Activity 4 (teacher demo)

• Run and set up LoggerPro to collect data from spectrophotometer
• Set vertical scale�to INTENSITY 🡪

Activity 5 (Your Turn; Group Work)

• Measure the wavelength of a green laser using the same procedure as Activity 2 (group activity, prize for most accurate group)
• Measure the wavelengths of light produced by a hydrogen lamp, a helium lamp, and a neon lamp. [Record 2 or 3 of the strongest wavelengths]
• Measure the wavelengths of light produced from flame tests of sodium and lithium salts.

Activity 6 (teacher demo)

• Explain helium emission near 588 nm, by looking up information from the NIST Atomic Spectra database

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Activity 7 (your turn)

• Explain emission lines from the lamps and from flame tests, by looking up information from the NIST Atomic Spectra database

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Lagniappe

• Aim a laser pointer at a wall

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• Observe what happens when you look at the laser spot on the wall through rainbow glasses.
• Repeat using the diffraction grating used in Activities 1-2. Observe what happens when you rotate the grating. Observe what happens when you use two gratings and rotate the second diffraction grating.
• How would you explain your observations with the “rainbow glasses”

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Lagniappe

• Observe the light produced by hydrogen, helium, and neon through the diffraction grating used in Activities 1-2.
• How do the colors observed through the grating correlate with the colors observed without the grating?

Lagniappe

• Observe light from fluorescent lamp in the room through a handheld spectrometer. Aim the slit at light source. Green line around 540-570 nm is due to Hg
• Use Vernier Spectrophotometer�to get a more accurate �measurement.
• Look up how electron �configuration of Hg �changes when the �green light is produced