Explain how the spectroscope will be calibrated

Quantitative Spectroscope and Visible Light Hands-On Labs Version 42-0305-00-01

Review the safety materials and wear goggles when working with chemicals. Read the entire exercise before you begin. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise.

Experiment Summary:

In this experiment, you will learn about light and how each light source creates its own unique spectra. You will learn about spectroscopes and how they are used to create and view emission spectra. You will build a diffraction grating spectroscope and will use it to view and draw the spectra of numerous light sources.

EXPERIMENT

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Learning Objectives Upon completion of this laboratory, you will be able to:

● Define the electromagnetic spectrum and explain its relationship to visible light.

● Describe how matter interacts with electromagnetic radiation.

● Draw emission lines for spectra.

● Compare and contrast diffraction grating spectroscopes and prism spectroscopes.

● Build a diffraction grating spectroscope.

● Use a spectroscope to view spectra of various light sources.

● Compare and contrast continuous and line spectra.

● Describe the relationship between wavelength and frequency.

● Calculate frequency from wavelength and wavelength from frequency.

Time Allocation: 2 hours

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Experiment Quantitative Spectroscope and Visible Light

Materials Student Supplied Materials

Quantity Item Description 1 Access to printer 1 Access to street light 1 Fluorescent light 1 Incandescent light 1 Pair of scissors 1 Pencil 1 Ruler 1 Sharp knife or box cutter 1 Tape, clear (such as Scotch® tape) 1 Tape light-blocking (such as duct tape or electrician’s tape)

HOL Supplied Materials

Quantity Item Description 1 Diffraction grating 1 Small cardboard box (8”L x 4”W x 3”D) 1 Spectroscope Grid Template (Included with Manual)

Note: To fully and accurately complete all lab exercises, you will need access to:

1. A computer to upload digital camera images.

2. Basic photo editing software, such as Microsoft Word® or PowerPoint®, to add labels, leader lines, or text to digital photos.

3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources.

Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.

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Experiment Quantitative Spectroscope and Visible Light

Background The light coming from the window, hall light, or desk lamp appears as white light, however; what is perceived as white light is actually composed of a combination of seven colors: red, orange, yellow, green, blue, indigo, and violet. These seven colors compose the spectrum of visible light. Visible light is the portion of the electromagnetic spectrum that is visible to the human eye. The electromagnetic spectrum is the entire range of all possible frequencies of electromagnetic radiation, ranging from radio waves to gamma rays. See Figure 1.

Figure 1. Electromagnetic spectrum. Visible light is located approximately at the center of the spectrum. Radio waves contain the longest wavelength and lowest frequency; gamma rays contain the shortest

wavelengths and highest frequency. © Milagli

The electromagnetic spectrum is arranged by wavelength and frequency, with radio waves containing the longest wavelengths and low frequency and gamma rays containing the shortest wavelengths and highest frequency. Visible light spans the electromagnetic spectrum from wavelengths of approximately 390 nm to 750 nm, and is further defined by the seven individual colors (purple, indigo, blue, green, yellow, orange, and red) in the visible light region of the electromagnetic spectrum. This is a continuous spectrum, and colors blend into each other with no empty or dark spaces between them (the spectrum consists of light of all wavelengths). See Figure 2.

Figure 2. Visible light region of the electromagnetic spectrum.

There are two important relationships involving the properties of electromagnetic radiation: the relationship between frequency and wavelength and the relationship between frequency and energy. Frequency refers to the number of wave peaks that pass a stationary point per unit time and is measured in units of s-1 (sometimes called reciprocal seconds). Since all light travels at the same speed, wavelength and frequency are related by the equation:

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Experiment Quantitative Spectroscope and Visible Light

Wavelength is often given in nm and will need to be converted to m.

The energy of a single photon, or smallest unit, of light in any portion of the electromagnetic spectrum can be calculated by the equation:

Visible light is a form of energy, released from an object (matter) upon exposure to heat or radiation. Emission (release of energy in the form of light) of energy from matter occurs when its electrons are excited and move to a higher energy level, and then subsequently return to a lower energy level. This difference in energy, when moving from the higher “excited” energy level to the lower energy level, is released in the form of visible light. See Figure 3. Every object that releases energy creates emission lines that are unique to that object. Emission lines, also referred to as spectral lines, are a series of bright lines at a specific wavelength in the visible region of the electromagnetic spectrum that are specific to a type of emitted energy. For example, light from the Sun, light from a fluorescent light bulb, and light from a neon light bulb all have their own unique set of spectral lines. See Figure 4.

Figure 3. Formation of emission lines and excitation and emission of energy.