# Physics 107 - Making Comparisons

Learning Goals:

•  How to use mean and standard deviation when comparing data
•  Scatter plots in a spreadsheet

Part I  -  Radiation Count Rate

You will be measuring the rate at which radioactive particles are measured close to an alpha-emitter. The radioactive particles are emitted randomly, so you will need to use the statistical techniques learned so far to come up with a measurement of the average count rate (in counts/minute) and the uncertainty in that count rate.

•  Sign out one of the radioactive sources and place it source-side up (the black material pointing up) beneath the geiger counter
•  Geiger counter height should be set at 2.0 cm
•  Spend 10 minutes with others at your lab bench, discussing what measurements to take in a strictly limited data-taking session of 20 minutes
•  Spend 15 minutes analyzing your data to determine the average counts per minute, and uncertainty in this average
•  Do not touch the apparatus any further - you will need to remeasure again at the end of the lab period.

Part II

Remeasure the pendulum period at angles from 5 to 25 degrees. Spend 5 minutes discussing what measurements to take in a limited period of 25 minutes You must ensure that you achieve at least 0.1% precision in the period in order to look for a small effect. Compare different angles by calculating t-values for different pairs of angles. Is there a significant angle-dependence?
Plot a scatter plot of the period (y-axis) versus angle (x-axis).

Part III

Remeasure the decay rate of the radioactive source. Are the counts per minute different than they were at the beginning of the lab period?

Marking Scheme

1 mark for writing down a plan for 20 minutes of data-taking.
3 marks for measuring the radiation count rate (including histogram, mean, standard deviation, and uncertainty in the mean).
1 mark for writing down a plan to re-measure pendulum periods in 25 minutes.
3 marks for high-precision measurments of pendulum period, including t-comparisons of different angles
2 marks for scatter plot of period versus angle
3 marks for second measurement of count rate and analysis
1 mark for conclusion on whether the count rate has become smaller