9702 · P5
Paper 5 Planning, Analysis & Evaluation flashcards
Revision flashcards for Cambridge 9702 Paper 5 Planning, Analysis & Evaluation (syllabus P5). Flip, recall, then mark a real past-paper question.
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What is a Worst Acceptable Line (WAL)?
The steepest or shallowest straight line that still passes through all error bars on the graph.
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How do you find gradient uncertainty from a graph?
$\Delta m = |m_{\text{LOBF}} - m_{\text{WAL}}|$ using a large triangle (≥ half the line length).
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What must Paper 5 Q1 include?
Labelled diagram, procedure, measurements, control of variables, data analysis, safety.
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Uncertainty in $y = 1/x$?
$\Delta y = \Delta x / x^2$ (same fractional uncertainty as $x$).
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Uncertainty in $y = \lg x$?
$\Delta y = \lg(x + \Delta x) - \lg(x)$ (or equivalent range method).
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Systematic error vs random error?
Systematic: consistent offset (accuracy). Random: scatter between repeats (precision).
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Accuracy vs precision?
Accuracy = closeness to true value; precision = repeatability of measurements.
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Adding absolute uncertainties?
When quantities are added or subtracted, add absolute uncertainties.
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Combining percentage uncertainties?
When multiplying/dividing or raising to a power, add fractional (percentage) uncertainties.
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Why use a large triangle on a graph?
Points far apart on the LOBF reduce uncertainty in the calculated gradient.
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What do error bars represent?
The range of plausible values for each measurement due to uncertainty.
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Paper 5 Q2 intercept uncertainty?
$\Delta c = |c_{\text{LOBF}} - c_{\text{WAL}}|$ using the same worst-acceptable-line method as gradient.
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When is a log–log graph used in P5 Q1?
When the suggested relationship is a power law — gradient and intercept yield constants $n$ and $E$.
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What improves precision in an experiment?
Repeat readings and average; use instruments with finer resolution.
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What are the 7 key elements required for a 15-mark Paper 5 planning question?
1. Defining the problem (IV, DV, controls). 2. Labelled diagram. 3. Method of data collection (step-by-step). 4. Choice of instruments and their precision. 5. Method of analysis (linearised graph). 6. At least one specific safety precaution. 7. Detail on ensuring reliability (e.g., repeat readings).
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How do you linearise the equation `V = V₀e^(-t/RC)` to find the time constant, τ = RC?
Take natural logs of both sides: `ln(V) = ln(V₀) + ln(e^(-t/RC))`, which simplifies to `ln(V) = - (1/RC)t + ln(V₀)`. This is in the form `y = mx + c`. Plot `ln(V)` on the y-axis against `t` on the x-axis. The gradient `m` will be `-1/RC`. Therefore, the time constant `RC = -1/gradient`.
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What is the rule for drawing a Line of Best Fit (LOBF)?
The LOBF should be a single, thin, continuous line that represents the general trend of the data. It should have a balanced distribution of plotted points above and below the line and should pass through as many of the error bars as possible.
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What is the definitive rule for drawing a Worst Acceptable Line (WAL)?
The WAL is the line of maximum or minimum slope that passes through *every single error bar*. It is typically drawn by pivoting on an extreme point of the first or last error bar to just touch an extreme point of the error bar at the other end of the graph.
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How is the final uncertainty in a gradient, Δm, determined and stated?
First, calculate the gradient of the Line of Best Fit (`m_LOBF`). Then, draw a Worst Acceptable Line and calculate its gradient (`m_WAL`). The uncertainty is the magnitude of the difference: `Δm = |m_LOBF - m_WAL|`. The result is stated as `m_LOBF ± Δm`.