Notes On Light And Spectra

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Light and Spectra
GEOS 105 – Astronomy with Lab

Pre-Lab Assignment
Print this out, complete it, and get it checked as you arrive in your lab section.

NAME: _____________________________

GEOS 105 Section ____

Reading Assignment:
In Discovering the Essential Universe read Blackbody Radiation, Identifying the Elements…, and
Atoms and Spectra (pages 73-85; Sections 3-12, 3-13, 3-14, 3-15, 3-16, 3-17, and 3-18)
Answer the following questions:

What is the numerical value of the speed of light?

2. How long does it take light to travel from the Sun to the Earth, a distance of 1.50 x 108 km?
(Show your work.)

3. Light can be described as a wave which has a certain wavelength and frequency. In the sketch below, label the wavelength and define wavelength and frequency.


b. Frequency


Does the speed of light depend on either wavelength or frequency?

©Jennifer L.B. Anderson, 2013
Geoscience, Winona State Univ.

Light & Spectra
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Below you will find a spectrum of visible light. What color is the light…

With the longest wavelength?


With the shortest wavelength?


With the highest frequency?


With the lowest frequency?


With the most energy?


With the least energy?

To the right is a sketch of electrons surrounding the nucleus of an atom.
10. Label the nucleus, the electrons, and the electron orbitals.
11. When a photon is absorbed by an atom, what happens to one of the electrons? Draw this on the sketch.

12. When a photon is emitted by an atom, what has happened to one of the electrons? Draw this on the sketch.

13. To the left are three different types of spectra. Identify which spectrum is shown. Your choices are Emission Spectrum,
Absorption Spectrum, and Continuous Spectrum.



©Jennifer L.B. Anderson, 2013
Geoscience, Winona State Univ.

Light & Spectra
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Light & Spectra
GEOS 105 – Astronomy with Lab
Assign group roles as usual, making sure each person’s role is different than the previous week.
Recorder ____________________
Task Minder ______________________

Reporter ____________________
Skeptic ___________________________

Tremendously large telescopes are used in astronomy to collect as much light as possible from very distant objects and their invention changed the way we were able to understand and view our
Universe. However, most objects are so far away from Earth that, even with the largest telescopes, they still appear only as points of light. Luckily, light carries a lot of information about any given object throughout the Universe and so we are able to study light and figure out things like what an object is made of, how fast it is moving, how far away it is and how hot it is. Light is amazing!! The instrument that we use to “read” all the information that light carries is called a spectroscope and the science is called spectroscopy. In this lab, you will use a spectroscope to explore many different light sources and you will learn about how we can tell what an object is made of by looking at the light that it emits (or absorbs).

©Jennifer L.B. Anderson, 2013
Geoscience, Winona State Univ.

52 meters

28 meters

40 meters

52 meters

An Analogy about Light…
Imagine that you have a quarry filed with water, a cliff on one side, and a slope on the other. Also imagine that you gathered a bunch of rocks that were all the same size and weight and threw them into the water, from different heights on the cliff.

Light & Spectra
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In general, rocks from higher up make larger splashes (they have more energy). As you can see, you could only make four different size splashes from the cliff on the left, while you could make any size splash you wanted to, within a certain range, from the slope on the right.

Consider the cliff side of the quarry above. Suppose you throw one rock from