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**Laboratory #5 **

**Fall 2017 **

**Inverse Square Law **

- This lab will be completed in class and you will need to work with a lab partner.
- Working with your lab partner(s), go to blackboard and complete the pre lab assessment for Lab #5.
- a) First complete the assessment using your account.
- b) Once you are finished, log out, let your lab partner log in, and repeat the assessment so that each person has completed it.
- Once each of you has completed the assessment, begin the lab.
- a) Get a light meter from your instructor. (You may have to wait for someone else to finish this section.) b) At the front of the room there is a bare light bulb.
- c) Turn off all of the other lights so that this is the only significant source of light in the room.
- d) Use the light meter to measure the brightness of the light at at least 5 different distances from the front of the room to the back.
- e) Use the tape measure to find the distance to each of these points.
- f) Fill out the brightness you measured and the distance at which you made the measurement on the Lab #5 spreadsheet.
- Save your data, send it to your lab partner(s), and compare your results with your classmates.
- On the worksheet, calculate the log of the brightnesses you measured and the log of the distance for each measurement.
- Make a plot of the brightness as a function of distance.
- Make a log-log plot of the brightness as a function of distance.
- Find the straight line that best fits your data on a log-log plot. Find the slope of that line.
- Prepare a lab report using the data you took in class, the two plots you made, and the answers to the questions below.
- a) You may hand write and scan it or you may use a word processor (e.g. Office or Powerpoint).
- b) Your report must be in a single PDF format document.
- c) You should do this lab with a partner and talk with them about the write up but this write up must be your own work in your own words.
- d) You can (and should) compare your results that other people took but for your report you must use the data you and your lab partner took not data taken by someone else.
- e) You must each submit your own report.
- f) The lab report should use complete sentences to describe what you did, and what you saw.
- g) Your instructor will give you additional instructions for the correct format and form of your report.
- h) When you have completed your lab report upload it to Blackboard using the link in the Lab 5 folder. 10.Do the post lab quiz on Blackboard. You may, but don’t have to, work with your lab partner on the quiz.
- You must upload your lab report and complete your post lab quiz within 7 days of your assigned lab time.

**Questions**

- What is the slope of the line that fits through your data on a log-log plot?
- What does that tell you about the relationship between the brightness you measured and the distance?
- What will the effects of other lights or reflections off of the walls be on your measurements?
- Will the data still be a power law?
- What would the slope of the line on a log plot be if brightness followed an inverse cubed law instead of an inverse squared law?