Energy production in the twenty-first century is changing as the world moves toward renewable and sustainable energy sources. Technologies like wind turbines, geothermal and hydroelectric generators, and solar cells are harnessing the energy available around us in nature to put it to use in our homes, schools, and offices.

By the end of this lab, you will have…

• … gained experience using the scientific process;
• … explored electrical power, specifically the relationships between current, voltage and power;
• … explored the concept of stored energy, specifically the change from mechanical to gravitational potential energy; and
• … designed an experiment to investigate what parameters affect wind turbine power output.

You will be working with the wind turbine setup. Use the turbine to raise various masses in order to generate work. You will design an experiment to investigate the relationship between work and power in the wind turbine.

Your TA will provide more details on each step, but you can consult the outline below as you progress. Remember to write down everything you see and do in your lab notebook. This document serves as a record of your experiment and it should include pictures, notes, data, calculations and conclusions.

Remember also that you will need to share your experiment and its results with the class at the end of the period. It may be helpful to use the whiteboards to make diagrams, notes, tables, or plots of information you want to communicate to others as you go.

Remember to write down everything you see and do in your group lab notebook.

• Make sketches, do calculations, take notes, and record observations. Your TA may ask to see your notebook during lab, and will read over it afterwards to assign a grade to the group.
• Use the digital group lab report to communicate the process and results from your experiment.

One of the important quantities you will want to measure today is the electrical power ($P$) delivered by your solar panel. In electrical circuits, work is done by moving electric charges around. Mathematically, power is work done ($W$) per unit time ($t$) (or equivalently, energy transferred, $E$ per unit time):

Electrical power (usually measured in units of watts, W) is calculated as the product of voltage ($V$, usually measured in units of volts, V) and current ($I$, usually measured in units of amps, A) as

In order to measure these quantities, we provide a small measurement board and two meters. The board has the following four connections:

• Source: Connect your source (e.g. your wind turbine or your solar cell) here.
• Load: Connect the “thing” you want to power with your circuit (e.g. a fan, a lightbulb, or an LED) here.
• Voltage: Connect a meter (set to DC voltage on the 20 V range) here.
• Current: Connect a meter (set to DC current on the 200 mA range) here.

We show a schematic and a photo of these connections in the figure below.

A schematic (top) and a photo (bottom) showing how to wire your circuit in order to measure both current and voltage with the meters. In this example, the ammeter reads a current of $I$ = 6.4 mA and the second meter reads a voltage of $V$ = 3.35 V. That means the total power is $P = IV$ = 21.4 mW. (Click on the photos to expand.)

Your measurement board may have red & black connectors, orange & grey connectors, or orange & brown connectors; all boards work the same. Plug all your red cables into one color (e.g. red or orange) and plug all the black cables into the other color (e.g. black, grey, or brown).

Consider: What happens as you change one variable and keep the others the same? In what ways can you measure your results? Can you make these measurements more accurate?

Consider: What is your independent variable? Your dependent variable? Your control variables? What is your hypothesis for this experiment and what specific prediction does it make?

Consider: What materials do you require? How will measurements be taken? By what methods are control variables being considered? What tools can be used to decrease the experimental error in the lab setup?

Consider: Do you trust your measurements? What uncertainties are present in the data and how can you quantify them? If measurements are repeated, do you get similar results?

Consider: How can you represent your results? Does any relationship exist between the variables being looked at? Are your data consistent with your prediction? Inconsistent? Inconclusive?

Consider: What do you want others to know about your experiment? How can you present your methods and results succinctly and clearly? Can you anticipate questions others might have? Can you think of improvements you’d make if you had more time?

At the end of the lab, you will need to record your final conclusions (about 1 or 2 paragraphs) in your lab report summing up the important results and take-away points from your experiment. Remember that you should only draw conclusions which are supported by the data, so be ready to back up any statements you make!

When you're finished, save your file as a PDF and upload it to Canvas. (Only one student needs to submit the report, but make sure everyone's name is on it!) If you make a mistake, you can re-submit, but work done after the end of the lab period will not be accepted.