OCR A Level Physics

Revision Notes

1.2.1 Presenting & Interpreting Results

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Presenting Observations & Data

  • Data can be presented in a variety of ways, such as on graphs, charts, or tables
  • Tables are applicable to any experiment yielding data
  • Graphs, on the other hand, are a little trickier depending on the type of data collected e.g. quantitative or qualitative
    • Quantitative data uses numerical values
    • Qualitative data is observed but not measured with a numerical value e.g. colour

Presenting Data in a Table

  • When taking readings, a sensible range should be taken, and the values should all be stated to an appropriate number of significant figures or decimal places
    • This is usually the same number as the resolution of the measuring instrument

  • The columns in any table should have both a quantity and a unit in their heading
    • When labelling columns, the names of the quantities should be separated from their unit by a forward slash ( / )

  • For data displayed in a table:
    • The first column should contain the independent variable
    • The second column should contain the dependent variable
    • If repeat readings of the dependent variable are required, these should be included with a column for the mean value at the end
    • Any columns required for processing data e.g. calculations should come after this

Stationary Wave Data Table Example, downloadable AS & A Level Physics revision notes

Conventions for presenting data in a table. The length is the independent variable and the frequency is the dependent variable

Presenting Data on a Graph

  • All readings, including suspected anomalous results, should be plotted on a graph so that they can be easily identified
  • When taking repeat readings, it is the mean value that is plotted
  • The way data is presented on a graph depends on what type of data it is

Discrete data
  • Only certain values can be taken, normally a whole number e.g. number of students
    • This should be displayed on a scatter graph or bar chart

Continuous data
  • Can take any value on a scale e.g. voltage in a circuit
    • This should be displayed on a line or scatter graph

Categorical data
  • Values that can be sorted into categories e.g. types of material
    • This should be displayed on a pie or bar chart

Ordered data
  • Data that can be put in ordered categories e.g. low, medium, high
    • This should be displayed on a bar chart

Processing, Analysing & Interpreting Experimental Results

  • After an experiment has been carried out, sometimes the raw results will need to be processed before they are in a useful or meaningful format
  • Sometimes, various calculations will need to be carried out in order to get the data in the form of a straight line
    • This is normally done by comparing the equation to that of a straight line: y = mx + c

Worked example

A student measures the background radiation count in a laboratory and obtains the following readings:Required Practical 12 WE Table 1, downloadable AS & A Level Physics revision notesThe student is trying to verify the inverse square law of gamma radiation on a sample of Radium-226. He collects the following data:Required Practical 12 WE Table 2, downloadable AS & A Level Physics revision notesUse this data to determine if the student’s data follows an inverse square law.Required Practical 12 Worked Example, downloadable AS & A Level Physics revision notes

Step 1: Determine a mean value of background radiation

    • The background radiation must be subtracted from each count rate reading to determine the corrected count rate, C

Step 2: Compare the inverse square law to the equation of a straight line

    • According to the inverse square law, the intensity, I, of the γ radiation from a point source depends on the distance, x, from the source

Intensity Equation

    • Intensity is proportional to the corrected count rate, C, so

    • The graph provided is of the form 1/C1/2 against x
    • Comparing this to the equation of a straight line, y = mx
      • y = 1/C1/2 (counts min–1/2)
      • x = x (m)
      • Gradient = constant, k

    • If it is a straight line graph through the origin, this shows they are directly proportional, and the inverse square relationship is confirmed

Step 3: Calculate C (corrected average count rate) and C–1/2 

Required Practical 12 WE Table 3, downloadable AS & A Level Physics revision notes

Step 4: Plot a graph of C–1/2 against x and draw a line of best fit

Required Practical 12 Worked Example(1), downloadable AS & A Level Physics revision notes

    • The graph shows C–1/2 is directly proportional to x, therefore, the data follows an inverse square law

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