## Physics 107 - Light Intensity I |

- Use of semi-log plots to reveal exponentail behaviour in scatter plots
- Refelecting on data while you take it, in order to continuously improve a scatter plot

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

To develop a model relating intensity to the number of plastic
sheets blocking the light, make measurements using a wide range of
number of sheets. To get started

- Write down a plan for
your first 10 measurments.

- Make measurements with several different numbers of sheets
(about 10 measurments) in front and remember to:

- adjust the light's distance so that the intensity reading is 500 lux without any sheets in front of it
- regularly remeasure the intensity with no sheets in the way is near 500 lux. Adjust distance slightly if it is has changed more than 1%.
- check your meter zeroing occasionally
- Plot the data on a linear-linear plot as you go along

- trying more thicknesses
- trying more extreme thicknesses
- retaking some data points (but do not throw data out)

Again, confer with other about what extra data you might need to improve the semi-log scatter plot.

Again, write down what you think needs improvement and what you measurments you need to do to improve things.

Continue until you are satisfied with your final result.

You need to include uncertainty in these plots and we will show
you how to handle that when rescaling graph axes.

Once you are satisfied with the data, and are satisfied with your
semilog plot, write down the model that describes intensity versus
number of sheets.

**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
critiqe after your second set of data and plan for more
data-taking

__3 marks__ for total, final data set with uncertainty

2 marks for
semi-log plot of data

2 marks for
conclusion, including estimate of the coefficient in the
exponential (what model describes the data, including estamates of
the coefficients)