Students’ Understanding of Spectra Seunghee Lee Department of Physics

Report
Students’ Understanding of
Spectra
Seunghee Lee
Department of Physics
Kansas State University
1
Introduction

Quantum mechanics is difficult both to teach and
learn in an introductory physics course.

The Physics Education Research Group has
developed curriculum to improve students’
understanding of quantum mechanics.

Visual Quantum Mechanics uses spectra of
different types of lamps.
2
Primary Research Question
Investigating students’
understanding of spectra
3
Research Questions
(Page 1 of 3)
1.
What do the students see when they are asked to
look at spectra?
2.
What connections do the students make between
spectra and their previous knowledge structures?
3.
How are the students’ understandings of light
related to its spectra?
4
Research Questions
4.
5.
(Page 2 of 3)
How do the students relate energy of light to its color?
Are there any misconceptions which students have
obtained from the classes or from everyday
experiences?
Do the students respond with consistent reasoning
concerning energy of light?
5
Research Questions
6.
7.
(Page 3 of 3)
How do the students change their conceptual models
immediately after instruction?
How do the students keep their knowledge acquired
from instruction? Do they revert back to their previous
models after period without further instruction on the
topics?
6
Phenomenographic Analysis

It was developed by Marton (1981, 1986) at Gutenberg
University in Sweden and has been used in educational
research areas to answer about students thinking and
learning.

Phenomenography is the research method, which
describes the qualitatively different ways of thinking in
description, analysis, and understanding of experience.
7
Research Methods
Summer
1999
Fall
1999
Spring
2000
Developed ‘Atomic Spectra’
Preliminary Study-Extra Credit Activity
Spring
2001
Surveys
Pre-Test
Post-Test I
Interviews
Post-Test II
8
Preliminary Study-Extra Credit Activity

67 Elementary Education Majors in Fall,1999 were asked
to observe the colored light and gas lamps.

We had a activity-based survey to see how students
observe the colored light and the gas lamp spectra.

They were asked to make yellow, purple, white, and
black, using red, green, and blue light with filters.

They looked at the hydrogen gas lamp through the
diffraction grating, and using the spectroscope.
9
Students’ Prior Experience of Spectra
experience
NO
39%
YES
61%
Elementary
School
21%
Not Indicated
34%
COLLEGE
6%
High School
18%
Junior High
School
21%
10
Number of Spectral Lines Observed and Prior Experience
11
Students’ Comparison of Gas Lamp and Fluorescent
Lamp Spectra

Differences




“The gas lamps have a less complete spectrum and a more
distinct color.” (20)
“The spectrum are more spaced and less color.” (12)
“The spectrum shape is thinner.” (5)
Similarities


“ They both have color spectrum.” (52)
“The spectrum are both same order.” (7)
12
Students’ Comparison of Gas and Fluorescent Lamp
Energy

Differences
“The gas lamps have less energy because the lights
aren’t as bright.” (40)
 “… Gas lamps do not have variety of energy.” (4)
 “…Gas lamps have higher energy because they
have more green and purple in it.” (4)


Similarities

“They both emit light.” (8)
13
Preliminary Comments




Unexpected number of students did not see
spectral lines when using the spectroscope.
Some students saw the continuous spectrum as
well as spectral lines.
The prior experience is most affected condition in
students’ learning.
The students’ ideas of energy of light were
focused on the intensity of light.
14
Interviews

We had 3 second year physics majors and 3 nonscience majors spring, 2000.

They observed an incandescent lamp, the colored
light coming through a filter, and a hydrogen gas
lamp.

They also examined the spectrum of each lamp
using the spectroscope.
15
Result: the Incandescent Lamp



The students tended to describe the light in terms
of color and brightness.
And the blue filter absorbs or blocks other colors
except blue.
Half of students expected to see a full spectrum
and/or just a blue part of spectrum when they
predict the spectra pattern of the blue light from
an incandescent lamp through blue filter.
16
Result: the Hydrogen Gas Lamp



Most students thought the brightness was related to the
number of photons.
One student thought that all the spectral lines of a
hydrogen atom had same intensity, but the eye perceived
the red was brightest.
Most students explained the spectral lines as energy
transition of the electron of hydrogen atom in the gas
tube.
17
Preliminary Comments




Most students explained the spectra pattern of
hydrogen gas lamp in the concept of energy level
model.
Students generally described the light as
brightness and color.
One student thought the brightness was only a
perception.
They couldn’t ignore the source of light, but they
sometimes ignored the role of a filter.
18
Preliminary Comments

All interviewees also saw the background
continuous spectrum as well as the spectral lines.
19
Written Survey





Question 1: students’ conceptions related the energy
emitted by the lamps supplied with different electric
power.
Question 2: compare the light energy of lamps emitting
different intensities.
Question 3, 4 & 5: the energy emitted by the lamps of
different colors.
Question 6: compare the light energy emitted by
Christmas tree lamps.
Question 7: the energy emitted by Light Emitting Diodes
(LEDs)
20
Courses

Contemporary Physics

Modern Medical Miracle Machines
All students have previously had 1 year of
Algebra-Based Physics.
21
Procedure

Pre-Test
4 weeks instruction

Post-Test I
10 weeks unrelated instruction

Post-Test II
22
Treatment

Visual Quantum Mechanics

Solids and Light Unit
 Spectra
 Energy
Levels
 Energy Bands
 Light Emitting Diodes (LEDs)
23
Analysis Method

Phenomenographic analysis method

Models from students’ responses.

Classify students’ answers into these models.

Validation by other researchers in this group.
24
Models: Pre & Post-tests

Intensity Model: Intensity is the only factor to
compare the energy emitted by light.

Appearance Model: If Red and Blue appear equally
intense, Blue must have a greater energy.

Red Model: Light energy is related to its color. Red
light has more energy than blue light.

Blue Model: Light energy is related to its color. Blue
light has more energy than red light.

Source Model: Energy is unaffected by coating of the
light bulb.
25
Students’ Model Profile by the Survey
In the context of monochromatic light in same
intensity
Percentage
100
80
Intensity Model
60
Appearance Model
Red Model
40
Blue Model
Source Model
20
0
Pre-Test
Post-Test I
Post-Test II
26
Students’ Model Profile by the Survey
In the context of monochromatic light in higher
intesity on the blue lamp
Percentage
100
80
Intensity Model
60
Appearance Model
Red Model
40
Blue Model
20
Source Model
0
Pre-Test
Post-Test I
Post-Test II
27
Students’ Model Profile by the Survey
In the context of monochromatic light in higher
intensity on the red lamp
Percentage
100
80
Intensity Model
60
Appearance Model
Red Model
40
Blue Model
20
Source Model
0
Pre-Test
Post-Test I
Post-Test II
28
Students’ Model Profile by the Survey
Percentage
In the context of transmitted light
100
90
80
70
60
50
40
30
20
10
0
Intensity Model
Appearance Model
Red Model
Blue Model
Source Model
Pre-Test
Post-Test I
Post-Test II
29
Students’ Model Profile by the Survey
Percentage
In the context of LED
100
90
80
70
60
50
40
30
20
10
0
Intensity Model
Appearance Model
Red Model
Blue Model
Source Model
Pre-Test
Post-Test I
Post-Test II
30
Students’ Model Profile by the Contexts
PRE-TEST
100
90
80
70
60
50
40
30
20
10
0
Intensity Model
Appearance Model
Red Model
Blue Model
Source Model
same intensity
higher intensity
on blue
higher intensity
on red
In the context of monochromatic light
In the context of In the context of
transmitted light
LED
31
Students’ Model Profile by the Contexts
POST-TEST I
100
90
80
70
60
50
40
30
20
10
0
Intensity Model
Appearance Model
Red Model
Blue Model
Source Model
same intensity
higher intensity
on blue
higher intensity
on red
In the context of monochromatic light
In the context of In the context of
transmitted light
LED
32
Students’ Model Profile by the Contexts
POST-TEST II
100
90
80
70
60
50
40
30
20
10
0
Intensity Model
Appearance Model
Red Model
Blue Model
Source Model
same intensity
higher intensity
on blue
higher intensity
on red
In the context of monochromatic light
In the context of In the context of
transmitted light
LED
33
Preliminary Comments

Main preconceptions are..



Intensity rules over color in comparing energies.
Red has greater energy than blue for same intensity.
If blue & red appear equally intense, blue must have greater
energy than red because red is more intense than blue.

Most students apply well their conceptions taken from
instruction to the questions.

Some students have difficulties applying models correctly
in the Christmas tree lamps question.
34
Conclusion



(Page 1 of 2)
The students transferred knowledge from the
mixing of paints to the mixing of lights.
The students who had no previous experience did
not observe the spectral lines over the continuous
background.
Most students explained the spectrum of a
hydrogen gas lamp using an energy level model.
35
Conclusion


The context of the question affected the students’
choice of conceptual models.
Instruction seems to …



(Page 2 of 2)
have a positive effect in almost all contexts.
not alter their preconceived ideas about Christmas
tree lamps.
New teaching materials could help students
change their conceptions significantly in most
contexts.
36
Suggestions for Further Studies



Prepare an interview protocol to see whether
comparison of the spectral patterns from different
lamps could help students to focus on the brighter
lines of a gas lamp spectrum.
Prepare an observation-based interview to see the
students’ conception of transmitted light.
Modify this survey and present it to a larger
number of students at various levels.
37

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