Data Collection (Edexcel International A Level Physics)

Revision Note

Katie M


Katie M



Data Collection

  • 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

Equation of a Straight Line Notes Diagram 1

A straight life graph showing the y-intercept and gradient, m

  • The mathematical skills required for the analysis of quantitative data include:
    • Using standard form
    • Quoting an appropriate number of significant figures
    • Calculating mean values

Using Standard Form

  • Often, physical quantities will be presented in standard form
    • For example, the speed of light in a vacuum equal to 3.00 × 108 m s−1This makes it easier to present numbers that are very large or very small without having to repeat many zeros
  • It will also be necessary to know the prefixes for the numbers of ten

Prefixes Table

Prefixes Table

Using Significant Figures

  • Calculations must be reported to an appropriate number of significant figures
  • Also, all the data in a column should be quoted to the same number of significant figures

Significant Figures Table, downloadable AS & A Level Physics revision notes

It is important that the significant figures are consistent in data

Calculating Mean Values

  • When several repeat readings are made, it will be necessary to calculate a mean value
  • When calculating the mean value of measurements, it is acceptable to increase the number of significant figures by 1

Calculating Mean Values, downloadable AS & A Level Physics revision notes

Graph Skills

  • In several experiments during A-Level Physics, the aim is generally to find if there is a relationship between two variables
  • This can be done by translating information between graphical, numerical, and algebraic forms
    • For example, plotting a graph from data of displacement and time, and calculating the rate of change (instantaneous velocity) from the tangent to the curve at any point

  • Graph skills that will be expected during A-Level include:
    • Understanding that if a relationship obeys the equation of a straight-line y = mx + c then the gradient and the y-intercept will provide values that can be analysed to draw conclusions
    • Finding the area under a graph, including estimating the area under graphs that are not linear
    • Using and interpreting logarithmic plots
    • Drawing tangents and calculating the gradient of these
    • Calculating the gradient of a straight-line graph
    • Understanding where asymptotes may be required

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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Katie M

Author: Katie M

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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