Physics 107 - Light Intensity I
- Use of semi-log plots to reveal exponentail behaviour in
- 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
- check your meter zeroing occasionally
- Plot the data on a linear-linear plot as you go along
REFLECTING ON YOUR DATA
Once you have an initial set of data, consult with another group and
decide what to do next to improve the quality of the data set. This
could include, but are not limited to:
Based on your discussion, write down what you think is wrong with
your data so far, and what you plan to do next, and then take more
- trying more thicknesses
- trying more extreme thicknesses
- retaking some data points (but do not throw data out)
THE SEMI-LOG PLOT
Produce a semi-log plot of your data so far to qualitatively confirm
whether or not it shows exponential decrease.
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.
for worked examples at the start
2 marks for description of experimental technique, for
your first measurements
2 marks for critique of first data and plan for more
2 marks for
critiqe after your second set of data and plan for more
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