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

The PLAN:• 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 bench)• Lab start by introducing the QUESTION• The question is related to the lecture subjects• The students have to define the parameters of the experiment• 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 bulb.

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 wavelengths.

Secondary analysis: compare light generated to power required.

Final analysis: draw conclusions.

The chemistry of greenWhy 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?

Electromagnetic Spectrum

.

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 source.

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.

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,

an Ocean Optics Spectrometer.

Learn how to use the

spectrometer.

You have 45 minutes

Let′s explore!

Let′s think!

Record your results for this fraction on the board.

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.

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 pre-lab activity. You will also

be held responsible for this material on the exams.