Light and Matter - Laboratory #3 Activities | PH 104, Lab Reports of Physics

Download Light and Matter - Laboratory #3 Activities | PH 104 and more Lab Reports Physics in PDF only on Docsity! Name: Lab Day and Time: Partner’s Name: PH104 Lab 3 Activities Light and Matter 3.1 Goals To understand how astronomers use light, you need to know something about how it interacts with matter, how it behaves, and what information can be determined from the light that is observed. It is, after all, the measurement of light from the distant stars and galaxies that is the primary way that we know about the universe around us. In this week’s lab, you will be analyzing light and making calculations that are the same as used by astronomers in finding out some pieces of this universe puzzle. At the end of this lab, you will be able to  make observations of some light phenomena.  understand the role of experimentation in answering questions.  take and analyze spectral data.  use the appropriate Doppler Shift equation to find the speed of an object. 3.2 The Electromagnetic Spectrum We’ll start by considering the whole of the electromagnetic spectrum – the entire range of possible light frequencies. The EM spectrum ranges from gamma-rays at the high energy end to radio waves at the low energy end of the spectrum. The only difference between the different types of EM radiation is their frequencies, and, thus, their wavelengths and energy levels. Task #1: In the table below, rank the types of EM radiation by frequency with the highest frequency wave being a 1, the next highest a 2, and so on. To do this, you’ll need to remember the relation between the speed, wavelength and frequency of a wave. Then, rank the types of EM radiation by energy from highest (1) to lowest (7). To do this, you’ll need to remember the relation between the energy and frequency of a wave. You do not need to calculate frequency or energy values to do this exercise. Look up the two relationships and write them down below: Relationship between, c, λ, and ν. ____________________________________ Relationship between E, ν, and h. ____________________________________ EM Type Wavelength (m) Frequency Ranking Energy Ranking radio 103 x-ray 10-10 microwave 10-2 ultraviolet 10-7 gamma rays 10-12 visible light 10-6 infrared 10-5 Table 3.1: Some Planetary Data Question #1: The visible part of the EM spectrum ranges from about 390 nanometers to about 720 nanometers. A nanometer (nm) is 10-9 meters or 1 billionth of a meter. The bluest light we see in a rainbow has a wavelength of about 400 nm; the reddest light we see in that rainbow has a wavelength of about 720 nm. Which color light (blue or red) is the highest in energy? Explain briefly. 3.3 Atomic Spectra As discussed in lecture and a bit in the PreLab, it was explained that when an element absorbs light, it can only absorb certain wavelengths of light. This is because the element’s electrons can only absorb certain amounts of energy when they jump up from a lower to a higher energy level. This means that if one shines white light through a gas (of some element) and then through a prism, one can see that some of the wavelengths of light will be missing from the continuous spectrum. This is a called an absorption spectrum and is characteristic of the gas (element) through which the white light passed. When an electron of some element drops from a higher to a lower energy level, it will release a specific amount of energy and thus will emit a photon of that specific energy which corresponds to a specific frequency. For any element, there can be many possible transitions but there are not an infinite number of possibilities. This means that the emission spectrum will be mostly dark except for those wavelengths that the element can emit. They appear as specific “lines” in the spectrum; colored lines if the frequencies happen to correspond to visible wavelengths. This emission spectrum is characteristic of the element that creates it. Since every element has a different set of energy levels that it can absorb or emit, looking at the spectrum is a very good way to identify what element(s) created the spectrum. You will take a look at some characteristic spectra. On the computer, open a browser (Internet Explorer or Mozilla) from the desktop. The course website (www.physics.oregonstate.edu/ph104) should open. (If not, open it.) One of the links at the top of the page is titled “Materials”. Click on this and then scroll down to the “Lab Materials”. Under “Lab Links” is a link called “SPECTRA”. Click on this. This opens a website from University of Oregon. It shows a periodic table of the elements. Clicking on any element, and it will display the visible range of the electromagnetic spectrum for that element. There is also an option for emission or absorption spectrum. Take a look at a few of the possible spectra by clicking on some different elements. Question #2: After looking at several of the emission spectra, what general observations can you make? From element to element, are there any patterns for the number of lines, the placement of the lines, the line brightness, the line thickness, etc… Question #3: Choose the element helium (He). (Near the top right.) Click back and forth between the absorption and emission buttons. What do you notice about the position of the dark lines in the absorption spectrum compared to the position of the bright lines in the emission spectrum? Explain briefly. Lab instructor check point ______________ 3.4 The Doppler Effect The Doppler Effect is critically important in the study of astronomy. It’s important that you have some familiarity with the effect as seen on spectra. Figure 3.1 shows three hydrogen gas emission spectra. The first, A, is a spectrum that was taken in a laboratory on Earth. There is no relative motion so it shows no Doppler Shift. Both B and C are spectra taken from clouds of gas in space – one of which is moving away from us, the other towards us. Figure 3.1: Sample Spectra from A) Hydrogen Gas at Rest in Lab, and B) and C) Hydrogen Gas Clouds in Space Question #7: The spectrum that shows the greatest shift (relative to A) will be from the cloud of gas that is moving the fastest (relative to us on Earth.) Which spectrum shows the greatest shift; which gas cloud is moving the fastest? Question #8: A redshifted spectrum is one that shows shifts to longer wavelengths. Which spectrum indicates a redshift? Is that from a gas cloud that is moving towards or away from us? Question #9: A blueshifted spectrum is one that shows shifts to shorter wavelengths. Which spectrum indicates a blueshift? Is that from a gas cloud that is moving towards or away from us? We can calculate how fast something is moving with respect to us from the size of the Doppler Shift. v = c x (λO – λ) / λO (1.1) where v is the velocity of the object (in km/sec). This can be positive (for objects moving towards us) or negative (for objects moving away from us.) c is the speed of light, 300,000 km/sec, λO is the reference (laboratory) wavelength, and λ is the shifted wavelength observed from the object. Task #4: Let’s do a couple of sample calculations using this Doppler Shift relationship (equation 1.1) Fill in the table below. Show your work for the calculations for spectrum B. (Note that the numbers in the data table below are not well represented (to scale) in Figure 3.1.) Use λO = 4102.0 Å, as the reference wavelength. Spectrum Measured Wavelength (Å) Velocity (km/sec) A 4102.00 B 4166.66 C 3935.33 Table 3.3: Doppler Shift Calculations Question #10: Did the velocity that came out negative (indicating that the object is moving away from us) match your answer earlier as to which gas cloud was moving away from us (question 8 or 9)? Lab instructor check point ______________ 3.5 Conclusion Spectral analysis is one of the most important tools that we have in astronomy. You should now see that spectra can help us identify the composition of celestial bodies and determine the speed of objects relative to us. Later, we will see that spectra are used to find surface temperature of distant stars as well as other things. Barium Calcium Helium Hydrogen Sodium Mercury Neon Strontium 4573.9 4251.1 4387.9 4102.0 4238.9 4046.6 4554.8 4030.4 4579.6 4312.7 4471.5 4340.5 4324.6 4077.3 4585.5 4438.5 4947.1 4430.6 4685.8 4861.3 4541.8 4358.0 4754.2 4607.3 5519.5 4456.2 4921.9 6562.8 4668.6 4916.7 4790.0 4714.1 5535.7 4481.8 5015.7 4747.1 4970.6 4816.1 4784.5 5777.7 4507.5 5875.6 4978.9 5460.7 5360.6 4811.3 5826.2 4861.1 6678.2 5148.4 5769.4 5383.5 4832.3 6063.8 5260.9 5153.4 5790.5 5412.9 4855.4 6110.7 5332.7 5688.2 6072.7 5715.0 4868.7 6129.8 5563.3 5895.9 6234.4 5868.6 4872.5 6498.8 5594.0 6161.7 6907.5 6128.5 4876.1 5865.7 6202.0 4876.3 6091.2 6249.3 4962.3 6147.6 6351.5 5156.1 6414.2 6382.9 6878.4 7111.2 6409.5 6892.6 6506.5 6929.5 7173.5 7245.2 Table 3.4: Spectral Lines for a few common elements