Presenting & Interpreting Results (OCR A Level Physics): Revision Note

Exam code: H556

Katie M

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Katie M

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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 notes

The 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 notes

Use 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

Answer:

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/C–1/2 against x

  • Comparing this to the equation of a straight line, y = mx

    • y = 1/C–1/2 (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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Katie M

Author: Katie M

Expertise: Physics Content Creator

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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