Q: How do you linearise H2 Physics practical data in a spreadsheet? A: Rearrange the physics model into straight-line form, calculate the transformed columns, plot an XY scatter graph, add a linear trendline or use LINEST, then interpret the gradient and intercept in terms of the original constants.
TL;DR
Linearisation means turning a curved physics relationship into a straight-line graph by choosing the right processed column.
For RC discharge, plot LN(Current) against time; the gradient is negative and the time constant is -1 divided by gradient.
Keep raw data unchanged, add processed columns beside it, and use an XY scatter graph instead of a line chart.
Fast answer for Paper 4 For RC discharge, plot lnI against t. If I=I0e−t/τ
Want supervised lab practice?
Explore practical lessons, with timings, fees, and locations on the programme page.
Status: SEAB H2 Physics 9478 requires spreadsheet use for practical assessment from the 2026 examination and provides an Excel reference guide for Paper 4.
Quick spreadsheet map
If the model looks like...
Create this column
Plot this
Exponential decay
LN(y)
LN(y) against x
Power law
LOG10(x) and LOG10(y)
LOG10(y) against LOG10(x)
Reciprocal relationship
1/x
y against 1/x
Area under graph
Delta x, mean y, strip area
Sum the strip areas
Concrete example: reading an RC gradient
If the trendline for LN(Current) against time is y = -0.42x - 3.10, then:
time constant = -1 / -0.42 = 2.38 s
The negative gradient is expected. Do not report a negative time constant.
1 | Linearisation choices
Choose the transformation from the equation, not from the graph shape by eye.
Original relationship
Spreadsheet columns to create
Straight-line graph
Gradient meaning
I=I0e−t/τ
t, LN(I)
lnI against t
−1/τ
y=axn
LOG10(x), LOG10(y)
lgy against lgx
n
y=a/x+b
1/x, y
y against 1/x
a
y=a+bx2
x^2, y
y against x2
Always keep raw data columns unchanged. Add processed columns beside them so a marker can follow the workflow.
2 | RC discharge and time constants
For a capacitor discharging through a resistor:
I=I0e−t/τ
Take natural logarithms:
lnI=lnI0−τt
Spreadsheet workflow:
Enter Time / s and Current / A.
Add a new column LN(Current).
Use =LN(B2) if current is in column B.
Plot LN(Current) against Time / s as an XY scatter graph.
Add a linear trendline and display the equation.
Calculate τ=−1/gradient.
If the trendline shows y = -0.42x - 3.10, then:
τ=−−0.421=2.38 s
The intercept is lnI0. To recover I0, use =EXP(intercept).
3 | Power laws and reciprocal rearrangements
For a power law:
y=axn
Taking base-10 logarithms gives:
lgy=lga+nlgx
The gradient of lgy against lgx is n. The intercept is lga, so a=10intercept.
For reciprocal relationships, do not force a curved graph to become straight by choosing a narrow range. Create a processed 1/x column and plot the dependent variable against it. This is common when a variable is inversely proportional to distance, resistance, or another measured quantity.
4 | Trendline equation or LINEST
The displayed trendline equation is quick, but LINEST is better when uncertainty matters.
the question asks for the standard error in the gradient;
you need more significant figures than the chart label displays;
you need to show a reproducible calculation route;
multiple processed columns make the chart equation hard to audit.
Use a chart trendline when the question only asks for a best-fit line and the gradient can be read from the displayed equation.
5 | Radians in spreadsheet trigonometry
Excel and most spreadsheet tools use radians in SIN, COS, and TAN.
If the angle column is in degrees, convert before applying trigonometry:
Angle / degree
Formula for sine
30
=SIN(RADIANS(A2))
45
=SIN(RADIANS(A3))
If you use =SIN(30), the spreadsheet treats 30 as 30 radians, not 30 degrees. That error can make a later gradient look physically impossible.
6 | Area under curve and trapezoidal summation
Some Paper 4 tasks ask for the area under a graph, not just a gradient.
Use trapezoidal summation between consecutive data points:
area strip=21(y1+y2)(x2−x1)
Then sum all strips.
Graph
Area meaning
Current against time
Charge transferred
Force against time
Impulse
Force against displacement
Work done
Spreadsheet column pattern:
Keep raw x and y columns.
Add Delta x as =A3-A2.
Add Mean y as =(B3+B2)/2.
Add Strip area as =C2*D2.
Use =SUM(E2:E20) for the total area.
Do not average all y-values and multiply by total time unless the data points are equally spaced and the question accepts a rough rectangle estimate. The trapezoidal method is the safer Paper 4 response.
7 | Common spreadsheet mistakes
Plotting a line chart instead of an XY scatter graph.
Putting transformed data on the wrong axis, so the gradient has the inverse meaning.
Using LOG10() when the model calls for natural logarithm, or using LN() and then interpreting it as lg.
Forcing the trendline through the origin without a physics reason.
Rounding transformed columns too early.
Interpreting a negative RC gradient as a negative time constant.
