Emitting to the TruthPage 158

Emitting to the TruthStart a new thread/topicLearning Target: What does color tell us

about the underlying structure of matter?Update TOC

Emitting to the TruthRead the Introduction p. 158 & 159

Emitting to the TruthWe are going to be looking at different sources of light.

Incandescent light bulb: an electric light which produces light with a filament wire heated to a high temperature by an electric current passing through it, until it glows

Emitting to the Truthfluorescent light bulb: an low pressure gas filled lamp that uses fluorescence to produce visible light.

Emitting to the Truthsunlight: a portion of the electromagnetic radiation given off by the Sun, particularly infrared, visible, and ultraviolet light.

Emitting to the TruthWe will be using a spectroscope, which is an instrument that separates light into its constituent wavelengths.

Emitting to the TruthThe spectroscope will show the spectrum of colors that make up the light that is being studied.

spectrum: the range of colors observed when white light is dispersed through a prism

Spectra is the plural of spectrum.

Emitting to the TruthEach element has a unique spectrum.

Spectra are like fingerprints.Spectra are characteristic properties of substances and can be used to identify an element.

Emitting to the TruthYour spectroscope has a scale on it to show the wavelength of each color that makes up the light source.

The lines that appear are called spectral lines.

Emitting to the TruthWavelength

Is the distance between the crests of wavesDetermines the type of electromagnetic energy

Emitting to the TruthElectromagnetic spectrum

Visible light is a small portion of the electromagnetic spectrum

The color depends on the wavelength

Emitting to the TruthLet’s look at the spectra for different

elements:Emission Spectra of ElementsBeloit College Emission & Absorption Spectra

Light 1

Light 2

Light 3

Light 4

Emitting to the TruthSet up a data table to capture the spectrum

for each light source you will be viewing.Use the spectroscope to view the light sourceUse colored pencils to sketch the spectrum in

your notebook.There are 11 lights that

you are observing. Answer 5a-e p. 160Answer R&C #1-4Read/Notes “Energy” p. 161-162

Light 1

Light 2

Light 3

Light 4

Incandescent LightContinuous

spectrumAll

wavelengths are present in the light that is emitted.

White Fluorescent LightFluorescent tubes contain

specific elements… producing thin line spectra with some continuous spectra between the bright lines.

Hydrogen Element TubeOnly 4 spectral lines are visible

through our spectroscope!Only these 4 wavelengths make

up the light that is emitted.

Emitting to the TruthFluorescent tubes contain specific elements…

producing thin line spectra.Incandescent Light bulbs have a thin wire ��

through which electricity runs and burns white-hot… like a campfire, or like the sun!

Remember that each color has a different wavelength, which means a different amount of energy…

Emission spectra can tell us about the �composition of objects… like stars for instance!

Take Home LessonsIn the colored light, blue light has a shorter

wavelength = higher frequency = higher energy(compared to red which has long wavelength)

Light is Energy!We can use a prism (or diffraction grating) to

separate light into an emission spectrum. It is very important to know that some of the

light is not visible to humans! It might be infrared, or ultraviolet radiation!

Take Home LessonsSometimes, scientists form explanations for

things they cannot observe directly. For instance, if you see a broken window and a baseball lying inside, it might be reasonable to infer that the ball did the damage.

It is reasonable to infer that energy is transferred from one ‘thing’ to another… light into heat, or chemical energy into mechanical.

Energy: The Ultimate Quick Change ArtistEnergy is the ability to do workEnergy can be measured only by what it doesEnergy is abstract - you cannot see it but you can

detect it by the changes it effectsEnergy can cause changes in temperature, height,

velocity, bonds in a molecule, the state of an electron around an atom

Energy is not created or destroyed - it just changes forms

You observe energy changes which lead you to make conclusions about how energy is distributed.

P&P #55a. Were all spectra continuous?Not all spectra were continuous. The

incandescent light bulb produced a continuous spectrum, and the fluorescent tube produced a partially continuous spectrum.

P&P #55b. Did all spectra produce thin lines of

color?The fluorescent tubes produced thin lines of

color.

P&P #55c. Did all spectra show bands of black space

with no color?No, the fluorescent tubes had bright lines,

but the space between the lines was mostly filled with color, not black lines.

P&P #55d. Were thin lines of color always separated

by the same amount of black space?No, the thin lines of color of different

elements are separated by different amounts of black space.

P&P #55e. Were thin lines of color always located in

the same place when comparing 2 different sources?

No, thin lines for the element and fluorescent tubes were in different locations.

R&C #1What function does energy serve in the flame

tests? What function does energy serve in the different light sources?

R&C #2Think about the spectra you might see when

viewing light from flame tests. Now remember the spectra from the light sources in this activity. Should spectra from flame tests be similar to any of the 3 light source spectra? If so, which ones and why?

R&C #3Think about the spectrum you might see

when viewing a white hot campfire. Should the spectrum from a campfire be similar to any of the 3 light source spectra? If so, which one or ones and why?

R&C #4Light is a form of energy. Otherwise oceans

would not warm and skin would not sunburn. Is every color of light emitted from a light source associated with exactly the same amount of energy? Connect your answer to evidence from flame tests and spectra.