Edexcel A-Level Physics Graphs

Review graphs in Edexcel A-Level Physics through straight-line comparisons, gradient and intercept readings, processed data and logarithmic plots.

Exam points

compare a physical equation with y = mx + c to identify the gradient or intercept
use a large triangle or y-intercept to determine constants from a best-fit graph
process logarithmic data to test exponential or power-law relationships from plotted gradients

Covered syllabus points

C.3.1—Translating between data forms C.3.2—Plotting two variables C.3.3—Linear relationships C.3.4—Slope and intercept C.3.5—Rate from a linear graph C.3.6—Tangents and instantaneous rates C.3.7—Instantaneous and average rates C.3.8—Area under a graph C.3.9—Graphical calculus concepts C.3.10—Interpreting logarithmic plots C.3.11—Testing laws with logarithmic plots C.3.12—Sketching modelled relationships

[Maximum number: 3]

A student investigated the damped oscillations of a pendulum using the apparatus shown.

The paper cone acted as a damper.
The student displaced the cone and allowed the pendulum to oscillate.
He measured the amplitude A every 5 oscillations and recorded the value to the nearest 5 mm.

Figure for Question C.3 Graphs question 1 — Edexcel A-Level Physics A2

The relationship between A and the number of oscillations n is

A=A_0 e^- n

where A_0 is the initial amplitude and is a constant.

Determine the value of A_0 from the graph.

A_0=

[Maximum number: 2]

A student investigated the damping of a rotational pendulum using the apparatus shown.

Figure for Question C.3 Graphs question 2 — Edexcel A-Level Physics A2

When the metal rod is rotated through an angle and released, the rod performs angular oscillations about a vertical axis through the wire. The plastic sheets dampen the oscillations as they move through the air.

The relationship between the maximum displacement angle heta and number of oscillations n is given by

$heta= heta_0e^{-\lambda n},$

where $heta_0$ is the initial displacement angle and $\lambda$ is a constant.

Explain why a graph of $\ln heta$ against n could be used to determine a value for $\lambda$ .

Taking natural logarithms gives

$\ln heta=\ln heta_0-\lambda n.$

This has the form y=c+mx, so a graph of $\ln heta$ against n is linear with gradient $-\lambda$ .

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Covered syllabus points

C.3 Graphs question 1

C.3 Graphs question 2