Anne Padias

Redesigning General
Chemistry at the
University of Arizona:
How to engage students?
Steve Brown, Gail Burd, John
Enemark, Anne Padias, John Pollard,
Vicente Talanquer, Wayne Wesolowski,
Vicki Wysocki
• Large lecture discussion sections abolished
• Replaced by discussions in the lab environment, max
24 students
• TAs use the same guiding PowerPoint presentation
(with notes)
• Small learning/discussion units of 4 students
• Concepts immediately reinforced by experimentation
• Progression of a lab:
• introduction of problem
• background discussion (let’s think)
• experiment (let’s explore)
• conclusion (let’s think)
• etc.
Lab units operate this way:
• Students belong to a peer group of 4 students (one
• Lab start by introducing the QUESTION
• The question is related to the lecture subjects
• The students have to define the parameters of the
• They have to discuss options in their groups
• They shuttle back and forth between “class” and “lab”
• They have to discuss the results at the end of the lab
Week 5
Making Light Efficiently
Today’s Agenda:
 Review understanding of light.
 Develop the day’s problem.
 Perform the first challenge: measure the light emitted by an incandescent light
 Analyze results: determine the amount of light generated at different
wavelengths. Determine the amount of energy generated at different wavelengths.
 Perform the final challenge: measure the light emitted by other light sources.
 Analyze results: determine the amount of light and energy generated at different
 Secondary analysis: compare light generated to power required.
 Final analysis: draw conclusions.
The chemistry of green
Why would
someone say that
the 21st century
must be the
“Green Century”?
Global Warming
Why the concern?
What do you understand by efficiency?
How would you express the efficiency of a
light source?
The efficiency of a light source is a measure of
the amount of energy produced as visible light
compared to the total energy emitted:
efficiency = visible light energy / total energy
Consider this source of light.
What other forms of energy are
produced, besides visible light?
Let′s think!
In your groups:
 Predict what you think graphs of light intensity
versus wavelength for an “ideal” light source and an
incandescent light bulb will look like.
 Based on the graphs, propose a strategy to
determine the efficiency of the light emitted by a light
 What will you need to make
this determination?
A spectrometer is an optical
instrument that allows us to
measure the amount of light
(number of photons) as a
function of wavelength.
The instrument
essentially counts the
number of photons
hitting the detector in a
specific period of time.
Let′s explore!
Your First Challenge
Obtain a graph (spectrum) of the light
output of an incandescent light bulb.
Save the spectrum and load it into a
spreadsheet program.
Available resources:
 an incandescent light bulb,
Learn how to
use the
 an Ocean Optics Spectrometer.
You have 45
Let′s think!
 Create a graph of your spectral data.
 Compare this spectra to your prediction. Discuss
with your group any differences.
 Using the spectral data determine the fraction of
light emitted by the incandescent light bulb that falls
in the visible region.
Record your results for this
fraction on the board.
Let′s think!
Economic efficiency
 For each source compare the light
emitted in the visible region with the power
rating (wattage) for that source.
 Discuss the results with your group. Are
they what you expected?
No Report
No report is required for
this experiment.
In lieu of a report your group
is to generate a results
presentation and answer a
few discussion questions.
Completion of this activity
will be counted as the
equivalent of another prelab activity. You will also
be held responsible for this
material on the exams.