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Tools and Inquiry — IB Physics skills

I.3.2 Evaluating in Physics — IB Physics HL Revision Notes & Topical Questions

5 min read 10 parts Lesson 22 of 22 1 quiz

📚 IB Physics HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Lesson summary

I.3.2 Evaluating in Physics — IB PHYSICS SL notes: Evaluate the hypothesis, errors, weaknesses, limitations and assumptions, and suggest realistic improvements.A critical reflection on the methodology.It identifies weaknesses and limitations of the work.The goal is to assess data…

  • Random errors
  • Systematic errors
  • It must be relevant
  • It must be realistic
  • Close the loop
  • Be specific

Part 1 of 8Purpose of evaluation

Purpose of evaluation
A critical reflection on the methodology.
It identifies weaknesses and limitations of the work.
The goal is to assess data quality and its impact on the conclusion, and to suggest realistic improvements.

Part 2 of 8Evaluating the hypothesis

Evaluating the hypothesis
The final comment on the hypothesis, following from the conclusion.
Even supporting data should be judged against uncertainties and errors.
  • A y-intercept that misses the origin suggests a systematic error and weakens the confirmation.

Part 3 of 8Random errors

Random errors
Random errors unpredictable variations that scatter results around the true value — they affect precision.
Examples and fixes.
  • Reaction time starting and stopping a stopwatch: time many oscillations and divide.
  • Parallax reading an analogue scaleview at eye level.
  • Coarse ruleruse a millimetre scale.
Minimising them.
  • Repeat trials and take an average.
  • Measure over many intervals and divide.
  • Use a more precise device with smaller intervals.

Part 4 of 8Systematic errors

Systematic errors
Systematic errors
Systematic errors flaws in method or apparatus that make results consistently wrong in the same direction — they affect accuracy.
Examples.
  • An uncorrected zero error on a balance or ammeter.
  • Unaccounted heat loss, which always makes the temperature change too small.
Reducing them.
  • Recalibrate apparatus.
  • Use different apparatus.
  • Adjust or correct the method.
On a graph they appear as an offset of the line from the origin.

Part 5 of 8Weaknesses, limitations and assumptions

Weaknesses
Weaknesses parts of the method that cause significant systematic or random error.
  • Timing a single pendulum swing makes reaction-time error extremely significant.
Limitations
Limitations factors that limit the scope of the conclusion.
  • Lengths only up to 1.00 m mean the T2 proportional to L conclusion may not hold for much longer pendulums.
Assumptions
Assumptions simplifications that are not perfectly true.
  • Air resistance negligible and string massless for a pendulum.

Part 6 of 8Realistic and relevant improvements

Every significant weakness needs a specific improvement.
It must be relevant
  • It must be relevant it directly addresses the weakness.
It must be realistic
  • It must be realistic doable in a school laboratory.
    • (a bomb calorimeter is not)
Close the loop
  • Close the loop weakness, its impact on the result, then the improvement.
  • Length measured to the bottom of the bob makes L too long and g too high; measure to the centre of the bob.
  • Manual timing causes scatter; use a light gate at the bottom of the swing.
  • Amplitude drifting beyond the small-angle range; fixed release point and video tracking.

Part 7 of 8Writing a good evaluation

Be specific
  • Be specific never blame "human error";
    • name the source, e.g. parallax reading the pointer position on the metre rule.
Prioritise
  • Prioritise focus on the one or two errors with the biggest impact on the result.
  • For a pendulum, period timing or effective length matter more than pivot friction.
Refer to your own data
  • Refer to your own data graphs, intercepts and observations, not a generic evaluation.
  • A non-zero intercept on R against L suggests contact resistance.

Part 8 of 8More from the specification

More from the specification
Evaluating Experimental Results Against Literature Values
  • In a scientific physics investigation, experimental calculated values are compared against accepted literature benchmarks from published research.
Calculating Percentage Error
  • The percentage error quantifies discrepancy between an experimental result and the accepted literature value, calculated using: Percentage Error = × 100%.
    • (|Experimental - Accepted| / Accepted)
Evaluating Systematic Errors and Concluding Investigations
  • When concluding an investigation, discrepancies exceeding experimental percentage uncertainty indicate systematic errors in apparatus or methodology, guiding targeted improvements in future measurements.
Percentage error
  • Difference from the accepted value as a percentage of it.
Percentage uncertainty
  • The absolute uncertainty divided by the value, times 100%.
Simple pendulum
  • A small bob on a light string of length L
Linear relationship
  • Relationship that gives a straight-line graph, y = mx + c.

Key terms

TermMeaning
Random errorUnpredictable variation that scatters results about the true value.
Systematic errorConsistent error in one direction that affects accuracy.
WeaknessPart of the method causing significant error.
LimitationFactor that limits the scope of the conclusion.
AssumptionSimplification that is not perfectly true.
ImprovementSpecific realistic change that fixes a weakness.

Avoid these mistakes

1
Blaming "human error" instead of naming a specific source.
2
Suggesting an improvement that is unrealistic for a school laboratory.
3
Listing errors without explaining their effect on the result.
4
Writing a generic evaluation that could apply to any experiment.
5
Confusing random errors (affect precision) with systematic errors (affect accuracy).

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