willis high school atomic physics workbook...when illuminated by light with a frequency of 4.56 ×...

Willis High School

Atomic Physics

Workbook

This workbook belongs to Period

Atomic Physics Pacing Guide

DAY DATE WORKBOOK LABORATORY ASSESSMENT

M 4/29 1 to 20

T 4/30 Blackbody Spectrum Lab

W 5/1 21 to 40

T 5/2 Atomic Physics Quiz 1 (1 to 38)

F 5/3 41 to 60

M 5/6 Photoelectric Effect Lab

T 5/7 61 to 80

W 5/8 Atomic Physics Quiz 2 (1 to 80)

Atomic Physics Workbook Due

Grading This Six Weeks

Quizzes are percent-correct, open-workbook, minor assignments (40%)

Workbooks are percent-complete, major assignments (60%)

Workbook Expectations

Answers shall have a complete response in complete sentences in a clean, readable form.

Problems shall show at least as much work as the example demonstrates.

Workbook Completion Evaluation Instructor Use Only

Section Maximum Points Awarded Points

Main Content 80

Lab Reports 20

TOTAL

Atomic Physics

Atomic Physics 1

Classical versus Modern Physics So far we have been studying classical physics. Classical physics reached its zenith in the late 19

th century. It covers the

world at a human scale and involves objects moving no faster than our fastest machines, in a near Earth gravity field, and large enough to see with a microscope. Classical physics works for most everyday activities. Late in the 19

th century, physicists began to look into areas beyond the realm of classical physics. The era of modern physics

began. For a very fast moving object (near light speed), the physics of special relativity apply. General relativity physics is used for objects in large gravity fields. Exploration of these topics is left to the student. Very small objects involve atomic and nuclear physics. Atomic physics includes quantum mechanics and deals with the electrons of atoms and how they relate with photons. Nuclear physics covers the nucleus of atoms and the elementary particles. Let’s begin with atomic physics.

History of the Atom Notes

The questions below can be answered by viewing Program 49, The Atom, from the series The Mechanical Universe and Beyond which can be found at http://www.learner.org/resources/series42.html, a part of the Annenberg Learner web site.

1. The video opens and promises to discuss a third story in addition to mechanics, electricity, and magnetism. This

third story is the study of . 2. The theory of matter discussion begins with a picture of Neils , who proposed a model of the

hydrogen atom.

3. Bohr proposed that the hydrogen atom resembled planetary motion with the electron going in orbits around the proton. (circular, elliptical, straight line, or curved line)

4. Bohr’s model assumed that the electron could exist only in certain specific orbits and radiated or absorbed energy

only when it .

5. James Clerk was the authority on electromagnetism and the atom.

6. John proposed the law of simple and multiple proportions of chemical combinations to form molecules.

7. Spectroscopes are used to analyze .

8. Maxwell thought that each atom vibrated at its own , like a violin string. Thus, the

frequencies of light from molecules would be related in a simple way.

9. The equation involving the Rydberg Constant was used to predict . (wavelengths, energies, momentum, or forces)

10. J.J. Thompson discovered that all atoms contained “corpuscles”, which we know as . He

developed the model of matter. (solid ball, planetary, or plum pudding)

11. Earnest Rutherford used alpha particles to bombard a thin, gold foil. Most alpha particles went straight through, but some bounced back. Rutherford compared this surprising event to firing a 15 inch shell at and having it return and hit him.

http://www.learner.org/resources/series42.html

2 Atomic Physics

12. Rutherford’s planetary atom model was flawed (according to classical physics) because the orbiting electron would continuously. (radiate, absorb, speed up, or slow down)

13. In Maxwell’s theory of light, the energy of light depended upon its intensity, and for Max Plank, it depended upon

the of the light.

14. Bohr proposed that only special orbits were allowed based upon the orbits angular . (momentum, energy, force, or time)

15. Bohr’s model predicted not only the spectral lines of the atom but also the of the atom, and it was

approximately half an angstrom (an angstrom is 10-10

m).

16. Why was Bohr’s theory accepted?

Quantization of Energy MAX PLANCK 17. Date and Location of Birth 18. Significant Achievements

19. Significant Awards 20. Date, Age, and Location of Death

Atomic Physics 3

QUESTIONS 21. What is a black body? 22. What is blackbody radiation? 23. What is the conflict known as the ultraviolet catastrophe? 24. How did Max Planck explain the experimental data for blackbody radiation? 25. What is a quantum?

4 Atomic Physics

26. What is a quantum state? 27. What is the relationship between a joule and an electron volt? According to Planck’s theory, the resonators absorb or give off energy in discrete units of light energy called quanta (now

called photons) by “jumping” from one quantum state to another. If the principal quantum number (n) changes by one unit,

the amount of energy radiated changes by hf. For this reason, the energy of a light quantum, which corresponds to the

energy difference between two adjacent levels, is given by the following equation:

ENERGY OF A LIGHT QUANTUM

E hf

energy = Planck’s constant x frequency

Planck’s constant (h) = 6.63 x 10

-34 J·s = 4.14 x 10

-15 eV·s

EXAMPLE Each photon of yellow light, the predominant color in sunlight, carries energy of 2.5 eV. What is the frequency of this light?

-15

2.5 eV

4.14 x 10 eV s

?

E

h

f

14

-15

2.5 eV6.04 x 10 Hz

4.14 x 10 eV s

EE hf f

h

Atomic Physics 5

PROBLEMS 28. A photon of light carries energy of 3.3 eV. What is the frequency of this light? (7.97 x 10

14 Hz)

29. A photon of light carries energy of 5.0 eV. What is the frequency of this light? (1.21 x 10

15 Hz)

30. A photon of light carries energy of 2.0 eV. What is the wavelength of this light? (1.66 x 10

-6 m)

31. A photon of light carries energy of 4.40 eV. What is the wavelength of this light? (2.82 x 10

-7 m)

6 Atomic Physics

32. What is the photon energy of light with a frequency of 3.62 x 1014

Hz ? (1.50 eV)

33. What is the photon energy of light with a wavelength of 9.45 x 10

-6 m ? (0.131 eV)

34. What is the photon energy of green light with a wavelength of 525 nm? (5.52 eV)

Photoelectric Effect ALBERT EINSTEIN

35. Date and Location of Birth 36. Significant Achievements

Atomic Physics 7

37. Significant Awards 38. Date, Age, and Location of Death QUESTIONS 39. What effect did scientists originally think that the intensity of light shining on a photosensitive surface would have

on electrons ejected from that surface? 40. How do observations of the photoelectric effect conflict with the predictions of classical physics? 41. How does Einstein’s theory resolve this conflict? 42. What are some applications of the photoelectric effect?

8 Atomic Physics

43. The year 1905 is considered a “miracle year” in physics because of what four papers Albert Einstein published in this year?

In order to be ejected from a metal, an electron must escape from the metal by overcoming the force that binds it to the metal. The amount of energy the electron must have to escape the metal is known as the work function, Φ, of the metal. The work function is equal to hft , where ft is the threshold frequency for the metal. Photons with energy less than hft do not have enough energy to eject an electron from the metal. Because energy must be conserved, the maximum kinetic energy of the ejected photoelectrons is the difference between the photon energy and the work function of the metal. This relationship is expressed mathematically by the following equation:

MAXIMUM KINETIC ENERGY OF A PHOTOELECTRON

maxKE hf

maximum kinetic energy =

(Plank’s constant x frequency of incoming photon) – work function

The work function (Φ) is the product of Plank’s constant (h) and the metal threshold frequency (ft), i.e. Φ = hft. The values in the table below shall be used for all photoelectric problems.

Work Functions of Metals Metal Φ (eV)

Potassium 2.30 Sodium 2.75 Aluminum 4.28 Tungsten 4.55 Copper 4.65 Iron 4.70 Gold 5.10

EXAMPLE Light of frequency of 1.00 × 10

15 Hz illuminates a metal surface. The ejected photoelectrons are found to have a maximum

kinetic energy of 1.86 eV. Find the threshold frequency for this metal.

max

15

-15

1.86 eV

1.00 x 10 Hz

4.14 x 10 eV s

?t

KE

f

h

f

maxmax

-15 15

14

-15

4.14 x 10 eV s 1.00 x 10 Hz 1.86 eV5.51 x 10 Hz

4.14 x 10 eV s

t t

t

hf KEKE hf hf hf f

h

f

Atomic Physics 9

PROBLEMS 44. What is the threshold frequency of a metal that ejects photoelectrons with a maximum kinetic energy of 1.23 eV

when illuminated by light with a frequency of 2.34 × 1015

Hz? (2.04 x 1015

Hz)

45. What is the threshold frequency of a metal that ejects photoelectrons with a maximum kinetic energy of 6.78 eV

when illuminated by light with a frequency of 4.56 × 1015

Hz? (2.92 x 1015

Hz)

46. What is the maximum kinetic energy of a photoelectron emitted from potassium when illuminated by light with a

frequency of 2.68 × 1015

Hz? (8.80 eV)

47. What is the maximum kinetic energy of a photoelectron emitted from sodium when illuminated by light with a

frequency of 8.89 × 1014

Hz? (0.930 eV)

10 Atomic Physics

48. What is the metal that ejects photoelectrons with a maximum kinetic energy of 1.61 eV when illuminated by light with a frequency of 1.62 × 10

15 Hz? (5.10 eV, gold)

Early Models of the Atom JOSEPH JOHN "J. J." THOMSON 49. Date and Location of Birth 50. Significant Achievements 51. Significant Awards 52. Date, Age, and Location of Death ERNEST RUTHERFORD 53. Date and Location of Birth 54. Significant Achievements

Atomic Physics 11

55. Significant Awards 56. Date, Age, and Location of Death QUESTIONS 57. What was the Newtonian model of the atom? 58. What was the Thompson model of the atom? 59. Based on the Thomson model of the atom, what did Rutherford expect to happen when he projected positively

charged alpha particles against a metal foil? 60. Why did Rutherford conclude that an atom’s positive charge and most of its mass are concentrated in the center of

the atom? 61. What was the Rutherford model of the atom?

12 Atomic Physics

62. What are two problems with Rutherford’s model of the atom?

Bohr’s Hydrogen Atom NIELS BOHR 63. Date and Location of Birth 64. Significant Achievements 65. Significant Awards 66. Date, Age, and Location of Death QUESTIONS 67. What was the Bohr model of the atom?

Atomic Physics 13

68. Bohr’s model of the atom follows classical physics in some respects and quantum mechanics in others. Which assumptions of the Bohr model correspond to classical physics and which correspond to quantum mechanics?

69. How does Bohr’s model of the atom account for the emission and absorption spectra of an element?

Atomic Spectra The energy of a hydrogen atom electron depends upon the electron level, n, which is the principal quantum number. The energy of an electron at any level can be calculated by:

2

13.6 eVnE

n

where n = 1, 2, 3,…

Level 1 (n = 1) is called the ground state and all other levels (n = 2, 3, 4,…) are called excited states. The energy of a photon absorbed or emitted must equal the difference in energy between the two levels an electron transits.

photon i f

hcE E E hf

14 Atomic Physics

EXAMPLE What is the frequency and wavelength of light emitted by a hydrogen electron that drops from the 2

nd energy level (n = 2)

to the 1st

energy level (n = 1)?

2

2 2

1 2

-15

8

13.6 eV

13.6 eV3.40 eV

2

13.6 eV13.6 eV

1

4.14 x 10 eV s

3.00 x 10 m/s

? and ?

n

i

f

En

E E

E E

h

c

f

15

-15

87

15

3.40 eV 13.6 eV 10.2 eV

10.2 eV2.46 x 10 Hz

4.14 x 10 eV s

3.00 x 10 m/s1.22 x 10 m

2.46 x 10 Hz

photon i f

photon

photon

E E E

EE hf f

h

cc f

f

PROBLEMS 70. What is the frequency and wavelength of light emitted by a hydrogen electron that drops from the 3

rd energy level

to the 1st

energy level?

Atomic Physics 15

71. What is the frequency and wavelength of light emitted by a hydrogen electron that drops from the 3rd

energy level to the 2

nd energy level?

Dual Nature of Light QUESTIONS 72. How does light behave at radio wavelengths and frequencies? 73. How does light behave at visible wavelengths and frequencies?

16 Atomic Physics

74. How does light behave at high frequencies and very short wavelengths?

Uncertainty Principle WERNER HEISENBERG

75. Date and Location of Birth 76. Significant Achievements 77. Significant Awards 78. Date, Age, and Location of Death

QUESTIONS 79. What does Heisenberg’s uncertainty principle claim? 80. How is this principle expressed mathematically?

Atomic Physics 17

Blackbody Spectrum Lab

Purpose

To understand the Blackbody radiation graph.

Background

Everything emits Electromagnetic (EM) radiation. The sun does, operating incandescent lights do. We do. (Stand near an

athlete who has been working out for an hour. You can feel the EM radiation (heat) being given off by the athlete) Buildings

do. (Stand near a brick building’s west wall just after sunset. You can feel the EM radiation being given off). Anything at a

higher temperature than its surroundings, gives off EM radiation. The amount of power liberated in the form of EM

radiation depends on the object’s temperature in Kelvin, and its size in m2. As you will find out, the wavelength of the EM

radiation is related to temperature.

It has been found that the total power of the EM radiation being emitted by an object is proportional to T4 (the fourth

power of the object’s temperature in Kelvin)!

This EM (heat) radiation, under investigation in this simulation, should not be confused with an object’s color due to

reflection. An apple, at room temperature, appears red because it absorbs all the spectral colors of the white light

illuminating it except for red. The heating coils in an operating toaster are red because they are at a high temperature. At

room temperature they are grey.

A blackbody, when illuminated by white light absorbs all the ROYGBIV spectral colors. The same “black body” illuminated by

an infrared source may not absorb all infrared wavelengths. The electromagnetic energy absorbed by a blackbody is

radiated back out at different wavelengths.

Remember, the temperature in Kelvin is the Celsius temperature plus 273.

Preliminary

Access the PhET web site; search for phet or enter url: http://phet.colorado.edu/.

Click on Play with sims…>

From the left hand menu pick Physics.

From the left hand menu pick Quantum Phenomena.

Choose Blackbody Spectrum from the choices to the right.

Investigate the things that can be changed in the simulation.

The simulation does not have a reset button, so just close and reopen the simulation to perform a reset.

Procedure

The violet end of the visible spectrum starts at what wavelength?

The visible spectrum ends with red at what wavelength?

18 Atomic Physics

Light wavelengths are often expressed in nanometers (10-9

m). With 1 µm = 1000 nm, express the range of visible light in

nanometers (nm).

What is the initial temperature shown for this electromagnetic blackbody source?

What would you say is the color of the electromagnetic blackbody source shown at the top as a star burst?

What would you say is the shape of the red line on the intensity-wavelength graph?

The energy output of the EM source is spread over a wide band of wavelengths and varies in strength. At what wavelength

is the source’s output intensity the greatest?

Lower the temperature of the source. What temperature did you choose?

Describe the change in color of the source.

Describe the change in shape of the graph.

How does the wavelength of the maximum intensity change?

Atomic Physics 19

Raise the temperature of the source. What temperature did you choose?

Describe the change in color of the source.

Describe the change in shape of the graph.

How does the wavelength of the maximum intensity change?

At what Celsius temperature would an oven heating element just begin to glow red?

What does this simulation assume is the average Celsius temperature of the earth’s surface?

We see the earth by reflected light, but why don’t we see the earth glowing except at a few spots where there is an active

volcano?

Which color of visible light has the lowest temperature?

Which color of visible light has the highest temperature?

20 Atomic Physics

Photoelectric Effect Lab

Purpose

To investigate the nature of the photoelectric effect and work function

Background

When light shines on a polished metal surface, electrons can be ejected from the metal. This is the photoelectric effect, a cornerstone of our understanding of light as a particle. When we discuss the particle nature of light, we refer to light particles as "photons." The use of photons to generate an electric signal is used in light-activated circuits and in the soundtrack strip of cinematic films. It was Einstein's explanation of the photoelectric effect, not his work on relativity, which was honored in his Nobel Prize.

The energy levels of atomic particles are so small that a different energy unit is typically used.

electron volt (eV) = 1.6 x 10-19

joules (J)

Preliminary

Access the PhET web site; search for phet or enter url: http://phet.colorado.edu/.

Click on Play with sims…>

From the left hand menu pick Physics.

From the left hand menu pick Quantum Phenomena.

Choose Photoelectric Effect from the choices to the right.

Procedure

PART A: EXPLORATION

Step 1: Open the simulation. Set the metal to Sodium and the wavelength to 400 nm. In the Options menu, select "Show photons." Set the battery voltage to zero volts.

Step 2: Slowly move the intensity slider from 0% to 100% and observe the photoelectric effect. The electrons emitted from the metal are called "photoelectrons." They have the same mass and charge as any other electron.

Step 3: Move the wavelength selector back and forth and observe the results. Try changing the intensity at various wavelengths to see what effect that has.

Step 4: Carefully find the threshold wavelength (λt) for sodium. What is the wavelength of the lowest energy light at which electrons are emitted?

threshold wavelength (λt) = ___________________________________________________ nm

Atomic Physics 21

Step 5: Use the threshold wavelength (λt) to calculate the threshold frequency (ft). Show the calculation and solution. Remember that a nanometer (nm) is 10

-9 m.

Remember: c f so: t

t

cf

where c = 3 x 10

8 m/s

threshold frequency (ft) = Hz

Step 6: Use the threshold frequency (ft) to calculate the work function (Φ) of sodium. Show the calculation and solution.

Remember: thf where h = 4.14 x 10-15

eV·s

work function (Φ) = eV

Step 7: Set the wavelength to 400 nm and intensity to 100%. Notice the value of the current in the circuit. Adjust the setting on the battery to cut off the current. That is, set the voltage so that the current is just brought to zero.

cut-off potential at 400 nm = V

Step 8: Change the wavelength by 100 nm in such a way that current once again flows.

wavelength = nm

22 Atomic Physics

PART B: PHOTOCIRCUIT EXPERIMENT WITH ZINC

Step 1: Switch the metal to zinc. Set the battery voltage to zero volts.

Step 2: Find the threshold frequency (ft) and the work function (Φ) for this metal. Record your data and calculations in the space below.

threshold wavelength (λt) = nm



Step 3: Reduce the wavelength by 20-40 nm. Record the new wavelength in the Data Table.

Step 4: Adjust the stopping potential of the battery so that it just barely stops the current. Notice that there are two methods for adjusting the potential. Use the method that allows for greater precision. When the condition is met, electrons are ejected from the metal and almost make it to the opposite electrode. But they return to the metal, and the current remains zero. Record the minimum stopping potential for this wavelength in the Data Table.

Step 5: Repeat the process of reducing the wavelength by 20-40 nm and changing the stopping potential. Mix it up a bit! Record the wavelength and stopping potential in the Data Table.

Step 6: Repeat until you have four data sets.

Data Table

Wavelength (data)

Frequency (calculate)

Photon Energy (calculate)

Stopping Potential

(data)

Sum (calculate)

nm Hz eV V

nm Hz eV V

nm Hz eV V

nm Hz eV V

Step 7: Calculate the photon frequency and energy. For the last column, add together the photon energy and stopping potential.

Describe the values of the last column and their relationship to the metal’s work function.

Atomic Physics 23

PART C: PHOTOCIRCUIT EXPERIMENT WITH COPPER

Step 1: Switch the metal to copper. Set the battery voltage to zero volts.









Data Table

Wavelength (data)



Stopping Potential

(data)

Sum (calculate)

nm Hz eV V

nm Hz eV V

nm Hz eV V

nm Hz eV V



24 Atomic Physics

PART D: PHOTOCIRCUIT EXPERIMENT WITH PLATINUM

Step 1: Switch the metal to platinum. Set the battery voltage to zero volts.









Data Table

Wavelength (data)



Stopping Potential

(data)

Sum (calculate)

nm Hz eV V

nm Hz eV V

nm Hz eV V

nm Hz eV V



Atomic Physics 25

PART E: PHOTOCIRCUIT EXPERIMENT WITH CALCIUM

Step 1: Switch the metal to calcium. Set the battery voltage to zero volts.









Data Table

Wavelength (data)



Stopping Potential

(data)

Sum (calculate)

nm Hz eV V

nm Hz eV V

nm Hz eV V

nm Hz eV V

Step 7: Calculate the photon frequency and energy. For the last column, add together the photon energy and stopping potential


26 Atomic Physics

Additional Notes

willis high school atomic physics workbook...when illuminated by light with a frequency of 4.56 ×...

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