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Analysing conclusions and evaluating experiments

Key idea: Analyse O-Level Physics practical results, draw evidence-based conclusions and match significant experimental errors to specific improvements.

  • SEC G3 Physics 2027
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Learning objectives

  • Measurements of length, mass, temperature, time interval, volume of liquids/solids and force (e.g. weight) using appropriate instruments
  • Determination of the density of a liquid, or of a regularly or irregularly shaped solid that sinks in water
  • Determination of the value of the acceleration of free fall
  • Investigation of the effects of balanced and unbalanced forces
  • The principle of moments
  • Determination of the position of the centre of gravity of a plane lamina
  • Investigation of the factors affecting transfer of energy by thermal processes
  • Determination of heat capacities of materials
  • Latent heat of substances
  • The law of reflection
  • Determination of the position and characteristics of an optical image formed by a plane mirror or a thin converging lens
  • The refraction of light through glass blocks
  • The principle of total internal reflection
  • The focal length of lenses
  • Determination of the speed, wavelength and frequency of waves
  • Determination of the resistance of a circuit component
  • Investigation of the magnetic effect of current in a conductor
  • Investigation of the effects of electromagnetic induction

1. Definition

Analysis, conclusions and evaluation (ACE) means processing evidence, deciding what relationship it supports, identifying important limitations and proposing improvements that directly address those limitations.

2. Key Ideas

  • Describe a relationship with direction and form: increasing, decreasing, linear, proportional or non-linear.
  • Support a conclusion using a calculated quantity, gradient, intercept or comparison.
  • Do not claim proportionality unless the evidence supports a straight line through the origin.
  • Distinguish random scatter from a systematic offset.
  • State how an error affects a result when its direction can be deduced.
  • Match each improvement to the named source of error.
  • Keep predictions within the measured trend unless a physical model justifies extrapolation.

3. Detailed Explanations

A. Move from pattern to conclusion

“Extension increases with force” describes a trend. “Extension is directly proportional to force because the best-fit graph is a straight line through the origin within experimental scatter” is a supported conclusion. If the line has a significant intercept, do not ignore it; consider zero offset, initial extension or whether proportionality is inappropriate.

B. Use evidence, not impressions

Compare repeated values, ratios, gradients or percentage differences. A conclusion should answer the stated question and refer to the evidence that matters. Avoid claiming that a small difference is significant when it is comparable to the measurement scatter or resolution.

C. Evaluate an error as a chain

Use source → effect → improvement:

Significant sourceEffect on evidenceMatched improvement
hand timing variesrepeated times scattertime more cycles, repeat and use the mean
constant zero errorevery reading shiftedmeasure the zero offset and apply a correction
parallax from changing viewpointsreadings may scatter or shiftread perpendicular to the scale using a fixed eye position
resistor heatsresistance changes during the runuse smaller current and open the switch between readings
heat escapes to surroundingscalculated thermal quantity may be biasedinsulate, use a lid and reduce transfer time

Repeating cannot remove a constant zero error. A higher-resolution instrument cannot correct a flawed alignment. The improvement must target the mechanism.

D. State limitations honestly

An experiment may support a relationship only over the measured range. A single anomalous result does not automatically disprove the trend, but it should be checked. If no accepted value is provided, do not invent one to claim accuracy.

4. Common Mistakes

  • Calling any upward graph “directly proportional.”
  • Restating raw readings instead of interpreting them.
  • Writing “human error” without a specific action or measurement.
  • Suggesting repeats for a systematic offset.
  • Naming an improvement without explaining how it reduces the error.
  • Claiming an effect direction that cannot be deduced.
  • Extending a conclusion far beyond the measured range.

5. Exam Tips

For an evaluation mark, write one complete sentence containing all three links: “Because …, the measured … is likely too high/low or scattered; therefore … would reduce this by … .” If the direction is genuinely uncertain, state that it increases scatter rather than guessing high or low.

6. Worked Examples

Modelled example 1

Evaluating an irregular-solid density method

Core

Problem

Air bubbles remain attached when an irregular solid is submerged for a density measurement. Explain the effect on the calculated density and give a matched improvement.
Study the worked solution

  1. Identify the affected measurement

    Method

    Recognise that attached air adds to the displaced volume.

    Reason

    The measuring cylinder records the space occupied by both the solid and trapped air.

    Working

    The measured volume V is too large.

  2. Propagate the bias

    Method

    Use the density relationship to determine the result direction.

    Reason

    For the same measured mass, dividing by an overestimated volume gives an underestimated density.

    Working

    ρ = m/V; V too large ⇒ ρ too small

  3. Match the improvement

    Method

    Remove the bubble mechanism before taking the final volume reading.

    Reason

    Repeating unchanged readings would reproduce the same directional bias.

    Working

    Wet the object, lower it slowly, tap it to release bubbles, then read the meniscus at eye level.

Guided practice 2

Supporting a force–extension conclusion

About 6 min

Problem

A spring gives the data below. State the relationship supported over this range and use the values as evidence.

F/N1.02.03.04.0
e/cm2.04.16.08.1

Write the evidence-based conclusion

Hints

Hint 1: compare changes or ratios
Check whether doubling force approximately doubles extension and whether e/F stays nearly constant.
Hint 2: scope the claim
Use “within experimental scatter” and limit the conclusion to the measured range.
View solution step by step

  1. Extract numerical evidence

    Method

    Compare extension per unit force across the readings.

    Reason

    A nearly constant ratio supports direct proportionality when the graph is consistent with the origin.

    Working

    e/F = 2.0, 2.05, 2.0, 2.025 cm/N

  2. State a bounded conclusion

    Method

    Describe the relationship and acknowledge the small scatter.

    Reason

    Experimental measurements need not produce identical ratios to support an approximate physical trend.

    Working

    Over 1.0–4.0 N, extension is directly proportional to force within the scatter, provided the best-fit graph passes through the origin within uncertainty.

Common misconception 3

Repeats do not remove a zero offset

Find and correct the mistake

Learner response

A length scale reads 0.4 cm when the true input is zero. A learner takes five readings, calculates their mean and claims that the zero error has been removed. Locate the first reasoning error and give the correct treatment.

Diagnose before viewing the correction

First error

View solution step by step

  1. Classify the error

    Method

    Treat the + 0.4 cm reading as a systematic zero offset.

    Reason

    The same shift affects every measurement in the same direction.

    Working

    Each raw reading equals true value + 0.4 cm.

  2. Apply a correction

    Method

    Subtract 0.4 cm from each affected reading or repair and re-zero the scale.

    Reason

    Averaging reduces random scatter but leaves a constant offset unchanged.

    Working

    L_corrected = L_observed-0.4 cm

Examiner practice 4

Heat loss in a specific heat capacity experiment

4 marks

Examination question

In an electrical heating experiment, the candidate assumes all measured electrical energy heats the block and calculates c = E/(mΔ T). Some energy heats the surroundings. State the effect on calculated c and propose a matched improvement with reasoning. [4 marks]

Write the source–effect–improvement chain

View solution step by step

  1. Trace the measurement effect

    2 marks

    Method

    Recognise that the block receives less energy than the measured electrical input.

    Reason

    Energy transferred to the surroundings does not contribute to the block’s temperature rise.

    Working

    The measured Δ T is smaller than it would be if all input energy heated the block.

  2. Determine the bias direction

    1 mark

    Method

    Apply the smaller denominator in c = E/(mΔ T).

    Reason

    The calculation still uses the full electrical input E while Δ T is reduced.

    Working

    The calculated c is too large.

  3. Match the improvement

    1 mark

    Method

    Insulate the block and improve thermal contact while reducing exposed transfer time.

    Reason

    These changes increase the fraction of measured electrical energy transferred to the block.

    Working

    Wrap the block in insulation and fit the heater and thermometer securely in suitable holes.

Challenge 5

Resistance drifting during a run

Minimal support

New context

During repeated current–voltage measurements, a resistor becomes warm and the calculated resistance rises as the run continues. Evaluate the limitation, its effect on the intended constant-temperature relationship and a matched improvement.

Attempt the evaluation without the worked chain

Hints

Hint 1: name the changed control
Temperature is no longer controlled while the electrical readings are collected.
Hint 2: match the improvement
Reduce current and switch-on time, or allow cooling between readings; repeats alone do not restore constant temperature.
View solution step by step

  1. Identify the limitation

    Method

    State that current heating raises the resistor’s temperature during the run.

    Reason

    The experiment intends to compare electrical behaviour while other conditions remain controlled.

    Working

    Later readings belong to a warmer resistor rather than the same constant-temperature state.

  2. Explain the evidence effect

    Method

    Connect the temperature drift to the rising calculated resistance.

    Reason

    For a metallic resistor, higher temperature generally increases resistance in this context.

    Working

    The apparent relationship includes both the imposed voltage/current change and an unintended temperature change.

  3. Give a matched improvement

    Method

    Use smaller currents, open the switch between readings and allow cooling before repeats.

    Reason

    These actions reduce the heating mechanism rather than only averaging its biased effect.

    Working

    Take paired meter readings promptly after closing the switch, then reopen it.

7. Mind Stretchers

Mind stretcher 1: Can a precise graph give an inaccurate result?Extension

Explain how closely grouped readings can produce a neat graph while the result remains inaccurate.

Show Answer

Closely grouped readings can produce a neat line while every value has the same calibration offset. Precision concerns agreement; accuracy concerns closeness to the accepted value.

8. Practice and next step

Take three vague improvements—“repeat,” “use better apparatus,” and “avoid human error”—and rewrite each as a source–effect–improvement chain. Then return to the O-Level Physics Practical Hub for applied contexts.

Continue with the next resource in this course.

Course and syllabus information
Course
SEC G3 Physics
Edition
SEC G3 Physics 2027