Systematic and random errors in measurement.pptx
- 1. Physics topic for senior secondary or A-Level Physics
- 2. How do errors arise? Two causes of error in measurement: Choice of instrument Techniques of measurement It is held that one’s experimental technique must reduce the uncertainties to the minimum possible The technique caused uncertainties are two kinds Systematic errors Random errors
- 3. Systematic error A systematic error occurs when readings are... Above or below the true value by fixed amount Error being in the same direction Features Systematic error can not be removed by taking a few readings and taking mean value It can be reduced by improving experimental technique
- 4. Three types of systematic error Type Main points Instrumental zero error -Scale or it’s pointer not at zero before the measurement starts Scale graduated or calibrated wrongly -Calibrations are marked wrongly at the instrument manufacturing site -Check for reading with other instruments Experimentalist’s reaction time -When the instruments are operated manually different people may report different readings with the same instruments
- 5. Random error It occurs when readings are scattered around the accepted value It affects the precision of the instrument To reduce the random error Take a few readings Find the mean or average value of readings In graphs to reduce random error: Draw the best fit line
- 6. Some examples of random errors Judgement or interpolation in rounding up the scale reading Timing without a reference marker While attempting to take reading of two variables at the same time Parallax error due to reading of scale from different angles of line of sight
- 7. Combining uncertainties In indirect measurement, often for a derived physical quantity, to get the value of a physical quantity, a few other quantities are measured with each of them having their own uncertainties Combine or add up all certainties to determine the value of uncertainty of the physical quantity being measured (for a = b + c or b – c combination error equation is Δa = Δb + Δc) Combine or add up all fractional uncertainties to determine the value of uncertainty of the physical quantity (for a = Kbc or Kb/c combination error equation is Δa = Δb/b + Δc/c)
- 8. Two simple rule statements for combining uncertainties Rule 1 For the physical quantities which are added or subtracted to give final results, add up absolute uncertainties For For the physical quantities which are either multiplied or divided, add up the fractional uncertainties