## Physics 107 - Light Intensity II |

- Use of log-log plots and other linearized plots to discover functions in scatter plots
- Comparing functions (models) to data using residual plots

- Reflecting on data while you take it, in order to continuously improve a scatter plot

First, go through worked example II and answer all of the
questions. Work in pairs on this and hand in when you are done.

Goal is to to develop a model
relating intensity to distance between the detector and lamp.

A few tips to get started:

- Experiment with the zero-ing of your meter. If it reads "CALO" when you try to zero it, switch on and off.
- A light shield is in place to reduce the effect of your
movements on the background light. Investigate how well this is
working and how carful you must be about your movements.

- Regularly check your meter zeroing as you proceed with
measurements

- Plot the data on a linear-linear plot as you go along
- Note that distance is the distance from the detector
element to the lamp filament. make sure the plane of
the lamp filament is perpendicular to the line between the lamp
and detector.

- Measure intensity versus distance, for distances from 50-150
cm.

- Plot the data on a linear-linear plot.
- Comment on the quality of your data plot and make a plan for any improvements to the measurements
- After collecting further data to the point where you are satisfied, move on to part II

- Use a log-log plot to see if the data follows a power-law
model

- Estimate the exponent in the power law using your log-log
plot.

- Comment on the quality of your data plot and make a plan for improvements to the measurements
- After collecting further data to the point where you are satisfied with you log-log plot, move on to part III
- note that any new data can be combimed with previous
data, especially if you have a few repeated data distances
to chack that there have been no significant changes over
time.

- For this experiment, the power law involves a simple, integer exponent.
- Use a stright line model corresponding to this simple power law and adjust one free parameter to get the model close to your data
- Plot the residuals (difference between model and data points)
and further adjust your free parameter to see if you can get
residuals that look randomly scattered around zero.

- Perforn measurments at closer distances

- Use the log-log and residuals plot to comment on the behviour
in closer.

**Marking Scheme
**2

__2 marks__ for description of experimental technique, for
your first measurements

__2 marks__ for critique of first data and plan for more
data-taking

2 marks for
critique after your first log-log plot and plan for more
data-taking

__3 marks__ for total, final data set with uncertainty

2 marks for
log-log plot of data

2 marks for plot of residuals

2 marks for
conclusion, including function that describes the far-field data
and comments on the near-field data.