CSEC Physics Lesson 2 | Graphs & Measurement

PHYS

CSEC Physics • Lesson 2 of 2Graphs & Measurement · Myers Science Hub Student Centre

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CourseCSEC Physics

Practice formatMCQ • Structured • Experimental

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Notes Video MCQ Structured Experiment

Learning objectives

Plot a graph using correctly labelled axes and suitable scales.
Draw a line of best fit and determine its gradient using a large triangle.
Report measurements/calculations to an appropriate number of significant figures.
Select a ruler, Vernier calipers, micrometer, balance or timer for an appropriate quantity.
Identify sources of measurement error and suggest improvements.

Core notes

Good graph practice

Give a meaningful title; place the independent variable on the horizontal axis; label each axis with quantity, symbol and unit; choose a convenient scale that uses much of the grid; plot fine crosses.

Best-fit line

A best-fit line shows the overall trend. It should have a reasonable balance of points on either side rather than simply joining dot-to-dot.

Gradient

Gradient = change in vertical quantity ÷ change in horizontal quantity. CXC guidance specifies using a triangle that covers at least half of the best-fit line. Derive and state the gradient unit.

Measurement

Length may be measured by ruler, Vernier calipers or micrometer depending on scale and precision. Mass uses a balance; time uses clocks/stop clocks. Discuss sensitivity, accuracy and range when comparing instruments.

Common lost marks: missing units in table headings, inconsistent significant figures, tiny gradient triangles, poorly chosen scales and conclusions that are not supported by the plotted data.

Video lesson

Verified CSEC-specific walkthrough of a simple-pendulum graph.

Paper 01-style MCQ

1. Which instrument is MOST suitable for measuring the diameter of a thin wire?UK • 1

Metre rule Measuring cylinder Micrometer screw gauge Stopwatch

2. When finding the gradient of a best-fit line, the chosen triangle should ideallyKC • 1

use two adjacent data points only. cover at least about half the length of the best-fit line. have no units. be drawn outside the graph.

Paper 02-style structured questions

3. A graph of T²/s² against L/m gives two well-separated points on the best-fit line: (0.20, 0.80) and (0.80, 3.20). Calculate the gradient and state its unit.UK • 4

ΔT² = 3.20−0.80 = 2.40 s² (1); ΔL = 0.80−0.20 = 0.60 m (1); gradient = 2.40/0.60 = 4.0 (1); unit = s² m⁻¹ (1).

4. A ruler has millimetre divisions. A student records a length as 12.347 cm. Explain why this is inappropriate and give a more suitable form.UK • 2

The ruler cannot justify that many decimal places / precision exceeds instrument sensitivity (1). A suitable record would be to the nearest 0.1 cm, e.g. 12.3 cm, depending on the observed reading (1).

Experimental analysis question

5. In a pendulum experiment one timing is much larger than the others at the same length. State TWO possible causes and describe how the student should respond before drawing the final graph.XS/AI • 6

Possible causes include reaction-time error, miscounted oscillations, accidental push, length changed, bob striking an object, excessive angle (1 each, max 2). Repeat the measurement under the same controlled conditions (1); do not automatically discard unless there is justification (1); calculate/compare repeat values and use a representative mean if appropriate (1); record anomaly/decision transparently before graphing (1).

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Graphs, Significant Figures & Measurement