Laboratory work No. 2 (resolutions, answers) in physics, grade 11 - Determination of a light wave using a diffraction grating
2. Install the screen at a distance L ~ 45-50 cm from the diffraction grating. Measure L at least 5 times, calculate the average value
5. Calculate the averages. Enter the data into the table.
6. Calculate the lattice period d, write its value in the table.
7. By measured distance
8. Calculate the wavelength corresponding to the red edge of the spectrum perceived by the eye.
9. Determine the wavelength for the violet end of the spectrum.
10. Calculate the absolute errors in measuring distances L and l.
L = 0.0005 m + 0.0005 m = 0.001 m
l = 0.0005 m + 0.0005 m = 0.001 m
11. Calculate the absolute and relative errors in measuring wavelengths.
Answers to security questions
1. Explain the principle of operation of a diffraction grating.
The principle of operation is the same as that of prisms - deflection of transmitted light at a certain angle. The angle depends on the wavelength of the incident light. The longer the wavelength, the larger the angle. It is a system of identical parallel slits in a flat opaque screen.
Click to enlarge
2. Indicate the order of the primary colors in the diffraction spectrum?
In the diffraction spectrum: violet, blue, cyan, green, yellow, orange and red.
3. How will the diffraction spectrum change if you use a grating with a period 2 times greater than in your experiment? 2 times smaller?
Spectrum in general case there is a frequency distribution. Spatial frequency is the reciprocal of the period. It is therefore obvious that doubling the period leads to a compression of the spectrum, and decreasing the spectrum will lead to a doubling of the spectrum.
Conclusions: A diffraction grating allows one to very accurately measure the wavelength of light.
Laboratory work No. 6
"Measuring the wavelength of light using diffraction grating»
Belyan L.F.,
Physics teacher
MBOU "Secondary School No. 46"
Bratsk city
Goal of the work:
Continue developing ideas about the phenomenon of diffraction.
Study a method for determining the wavelength of light using a diffraction grating with a known period.
k =-3 k=-2 k=-1 k=0 k=1 k=2 k=3
Equipment:
1.Ruler
2.Diffraction grating
3. Screen with narrow vertical slot in the middle
4. Light source – laser (monochromatic light source)
Diffraction grating
A diffraction grating is a collection large number Very narrow cracks, separated by opaque spaces.
a - width of transparent stripes
b - width of opaque stripes
d = a + b
d- diffraction grating period
Derivation of the working formula:
Maximum
Sveta
a
Lattice
Screen
d sin φ = k λ
because the angles are small, then
sin φ = tg φ, then
Measurement table
Spectrum order
V
a
m
d
m
m
10 -9 m
Wed
10 -9 m
COMPUTATIONS:
1 . =
2. =
3. =
avg =
Table values:
λ cr = 760 nm
In the output, compare the measured wavelength values and the tabulated ones.
Control questions:
1. How does the distance between the maxima of the diffraction pattern change as the screen moves away from the grating?
2. How many orders of spectrum can be obtained from the diffraction gratings used in the work?
RESOURCES:
Physics. Grade 11. Myakishev G.Ya., Bukhovtsev B.B., Charugin V.M.
Textbook for general education institutions.
Basic and profile levels.
http://ege-study.ru/difrakciya-sveta/
http://kaf-fiz-1586.narod.ru/11bf/dop_uchebnik/in_dif.htm
http://www.physics.ru/courses/op25part2/content/chapter3/section/paragraph10/theory.html#.WGEjg1WLTIU
Topic: “Measuring the wavelength of light using a diffraction grating.”
Lesson objectives: experimentally obtain a diffraction spectrum and determine the light wavelength using a diffraction grating;
cultivate attentiveness, kindness, tolerance while working in small groups;
develop interest in studying physics.
Lesson type: lesson in the formation of skills and abilities.
Equipment: light wavelengths, OT instructions, laboratory instructions, computers.
Methods: laboratory work, group work.
Interdisciplinary connections: mathematics, computer science ICT.
All knowledge real world
comes from and ends with experience
A.Einstein.
During the classes
I. Organizing time.
State the topic and purpose of the lesson.
ІІ. 1. Updating basic knowledge. Survey of students (Addendum 1).
Performing laboratory work.
Students are asked to measure the wavelength of light using a diffraction grating.
Students are united in small groups (4-5 people each) and together perform laboratory work according to the instructions. By using computer program Excel makes calculations and the results are entered into a table (in Word).
Evaluation criteria:
The team that completes the task first receives a score of 5;
the second – score 4;
third – rating 3
Life safety rules while performing work.
Work in groups under the guidance of a teacher.
Generalization and systematization of work results by students.
The result of the work is entered into a table on the computer (Addendum 2).
ІІІ.
Summarizing. Compare the results obtained with the tabular data. Draw conclusions.
Reflection.
Did everything turn out the way I planned?
What was done well?
What was done poorly?
What was easy to do and what was unexpectedly difficult?
Work in small group Did it help me or create additional difficulties?
VI. Homework.
Apply for work.
Repeat theoretical material on the topic “Interference and diffraction of light”.
Compose a crossword puzzle on the topic “Properties of electromagnetic waves.”
Appendix 1
1. What is light?
2. What does white light consist of?
3. Why is light called visible radiation?
4. How to decompose white light into a color spectrum?
5. What is a diffraction grating?
6. What can you measure with a diffraction grating?
7. Can two different colored light waves, for example red and green radiation, have same lengths waves?
8. And in the same environment?
Addendum 2
Red10 -7 m
Orange
10 -7 m
Yellow
10 -7 m
Green
10 -7 m
Blue
10 -7 m
Blue
10 -7 m
Violet
10 -7 m
Laboratory work
Subject: Measuring the wavelength of light.
Goal of the work: measure the wavelength of red and purple flowers, compare the obtained values with the table ones.
Equipment: electric light bulb with a straight filament, a device for determining wavelength of light.
In this work, to determine the light wavelength, a diffraction grating with a period of 1/100 mm or 1/50 mm is used (the period is indicated on the grating). It is the main part of the measuring setup shown in the figure. The grid 1 is installed in a holder 2, which is attached to the end of the ruler 3. On the ruler there is a black screen 4 with a narrow vertical slot 5 in the middle. The screen can move along the ruler, which allows you to change the distance between it and the diffraction grating. There are millimeter scales on the screen and ruler. The entire installation is mounted on a tripod 6.
If you look through the grating and the slit at a light source (an incandescent lamp or a candle), then on the black background of the screen you can observe diffraction spectra of the 1st, 2nd, etc. orders on both sides of the slit.
Rice. 1
Wavelengthλ determined by the formulaλ = dsinφ/k , Whered - lattice period;k - spectrum order; φ - the angle at which the maximum light of the corresponding color is observed.
Since the angles at which the 1st and 2nd order maxima are observed do not exceed 5°, their tangents can be used instead of the sines of the angles. From the figure it is clear thattgφ = b/a . DistanceA count using a ruler from the grille to the screen, the distanceb - along the screen scale from the slit to the selected spectrum line.
Rice. 2
The final formula for determining the wavelength isλ = db/ka
In this work, the measurement error of wavelengths is not estimated due to some uncertainty in the choice of the middle part of the spectrum of a given color.
The work can be performed using instructions No. 2 or No. 2
Instruction No. 1
Progress
1. Prepare a report form with a table to record the results of measurements and calculations.
2. Assemble the measuring setup, install the screen at a distance of 50 cm from the grid.
3. Looking through the diffraction grating and the slit in the screen at the light source and moving the grating in the holder, install it so that the diffraction spectra are parallel to the screen scale.
4. Calculate the red wavelength in the 1st order spectrum to the right and left of the slit in the screen, determine the average value of the measurement results.
5. Do the same forotherscolorov.
6. Compare your results withtabularwavelengths.
Instruction No. 2
Progress
Measure the distance b to the corresponding color in the spectrum of the first line to the left and right of the central maximum. Measure the distance from the diffraction grating to the screen (see Figure 2).
Determine or calculate the grating period d.
Calculate the length of light for each of the seven colors of the spectrum.
Enter the results of measurements and calculations into the table:
b ,left,m
b ,right,m
b ,average,m
A ,m
Order
spectrumk
Lattice period
d ,m
Measuredλ , nm
Fiolet
Synth
Blue
Zelenth
Yellow
Orangeth
Red
4. Calculate the relative error of the experiment for each color using the formula
Federal State Educational Institution
higher professional education
"Siberian Federal University"
Institute of Urban Planning, Management and Regional Economics
Department of Physics
Lab report
Measuring the wavelength of light using a diffraction grating
Teacher
V.S. Ivanova
Student PE 07-04
K.N. Dubinskaya
Krasnoyarsk 2009
Goal of the work
Study of light diffraction on a one-dimensional grating, measurement of light wavelength.
Brief theoretical introduction
A one-dimensional diffraction grating is a series of transparent parallel slits of equal width a, separated by equal opaque spaces b. The sum of the sizes of the transparent and opaque areas is usually called the period, or lattice constant d.
The grating period is related to the number of lines per millimeter n by the relation
The total number of grid lines N is equal to
where l is the width of the grating.
The diffraction pattern on a grating is determined as the result of mutual interference of waves coming from all N slits, i.e. The diffraction grating performs multi-beam interference of coherent diffracted beams of light coming from all slits.
Let a parallel beam of monochromatic light with wavelength λ be incident on the grating. Behind the grating, as a result of diffraction, the rays will propagate in different directions. Since the slits are at equal distances from each other, the path differences ∆ of the secondary rays formed according to the Huygens–Fresnel principle and coming from neighboring slits in the same direction will be identical throughout the entire lattice and equal
If this path difference is a multiple of an integer number of wavelengths, i.e.
then, during interference, main maxima will appear in the focal plane of the lens. Here m = 0,1,2, … is the order of the main maxima.
The main maxima are located symmetrically relative to the central, or zero, with m = 0, corresponding to light rays that passed through the grating without deviations (undiffracted, = 0). Equality (2) is called the condition for main maxima on the lattice. Each slit also forms its own diffraction pattern. In those directions in which one slit produces minima, minima from other slits will also be observed. These minima are determined by the condition
The position of the main maxima depends on the wavelength λ. Therefore, when white light is passed through a grating, all maxima, except for the central one (m = 0), will decompose into a spectrum, the violet part of which will face the center of the diffraction pattern, and the red part will face outward. This property of a diffraction grating is used to study the spectral composition of light, i.e. a diffraction grating can be used as a spectral device.
Let us denote the distance between the middle of the zero maximum and the maxima of the 1.2, ... mth orders, respectively, x 1 x 2 ... x t and the distance between the plane of the diffraction grating and the screen -L. Then the sine of the diffraction angle
Using the last relation, from the condition of the main maxima one can determine λ of any line in the spectrum.
The experimental setup contains:
S - light source, CL - collimator lens, S - slit for limiting the size of the light beam, PL - focusing lens, DR - diffraction grating with a period d = 0.01 mm, E - screen for observing the diffraction pattern. To work in monochromatic light, filters are used.
Work order
We arrange the installation parts along 1 axis in the indicated order, and fix a sheet of paper on the screen.
Turn on the light source S. Install a white filter.
Using a ruler attached to the installation, measure the distance L from the grille to the screen.
L 1 = 13.5 cm = 0.135 m, L 2 = 20.5 cm = 0.205 m.
We mark on a piece of paper the midpoints of the zero, first and other maximums to the right and left of the center. WITH extreme precision measure the distance x 1, x 2.
Let's calculate the wavelengths transmitted by the filter.
Let's find the arithmetic mean value of the wavelength using the formula
Let's calculate absolute error measurements using the formula
where n is the number of changes, ɑ - confidence probability measurements, t ɑ (n) – the corresponding Student coefficient.
We write the final result in the form
We compare the obtained wavelength with the theoretical value. We write down the conclusion of the work.
Progress
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Maximum order |
X m to the right of 0 |
X m to the left of 0 |
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Light filter - green |
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5.3 * 10 -5 cm |
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5.7 * 10 -5 cm |
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6.9 * 10 -5 cm |
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Lesson-research
Self-control table
Testing Lesson-research on the topic “Determination of the wavelength of light” Self-control tableFull name of student ___________________________
Testing
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