Physics 5054 · Chapter 26 of 26

Practical skills: Paper 4 Alternative to Practical

10 revision notes on Practical skills: Paper 4 Alternative to Practical for Cambridge O Level Physics (5054). Every Paper 4 (Alternative to Practical) paper since 2010, with mark schemes, in Yearly papers.

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About this chapter

Syllabus: Experimental skills (AO3)
Section: Paper 4: Alternative to Practical (1 hour, 40 marks, 20%)
Level: All candidates
Paper 4: 1 hour · 40 marks · 20% of the grade
Every paper: Q1 10 · Q2 10 · Q3 14 (graph) · Q4 plan 6
Always tested: a graph, a table, a calculation to 2-3 s.f., a conclusion, a plan
Same skills as: the Practical Test (Paper 3)
Reading time: 10 notes · about 153 min
Practise with: Every Paper 4 (Alternative to Practical) paper since 2010, with mark schemes, in Yearly papers.

Study these notes in order

10 notes cover this chapter. Work through them 1 → 10: each one ends with a quiz, so you know you're ready for the next.

Start here · Note 1 of 10 · 15 min read The Alternative to Practical paper: how it works and how to score

The Alternative to Practical paper

Note 2 of 10 · 18 min read Measurements and readings: scales, precision, zero error and parallax

Measurements and readings

Note 3 of 10 · 13 min read Tables and calculations: headings, units and significant figures

Tables and calculations

Note 4 of 10 · 17 min read Graphs: axes, best-fit lines, gradients and intercepts

Graphs

Note 5 of 10 · 14 min read Conclusions, errors and improvements

Conclusions, errors and improvements

Note 6 of 10 · 18 min read Variables and planning an investigation

Variables and planning

Note 7 of 10 · 17 min read Mechanics experiments: density, springs, balancing and pendulums

Mechanics experiments

Note 8 of 10 · 13 min read Thermal experiments: cooling, heating and temperature

Thermal experiments

Note 9 of 10 · 15 min read Optics experiments: ray tracing, blocks and lenses

Optics experiments

Note 10 of 10 · 13 min read Electrical experiments: circuits, meters and resistance

Electrical experiments

Formula bank

Every formula and rule in this chapter. All Physics formulas on one page →

The Alternative to Practical paper: how it works and how to score

The paperLearn it1 hour · 40 marks · 20% of the gradeSame skills as the Practical Test, but you only read about the experiment.Use it when planning your time: about 1 minute per mark.

Every answer hasLearn ita value, a unit, a sensible precisionA reading to the scale's precision; a calculated value to 2 or 3 s.f.Use it when any 'record' or 'calculate' line.

Accurate vs preciseLearn itaccurate = close to the true value; precise = readings close to each otherUse it when an 'evaluate' or 'suggest' question.

Equal within the limitsLearn itvalues within 10% of each other count as equalAlways back the statement with a calculation.Use it when 'Do the results support…?', 'Are the values equal?'

Measurements and readings: scales, precision, zero error and parallax

Value of one divisionLearn it\(\dfrac{\text{difference between two labelled marks}}{\text{number of divisions between them}}\)Use it when every analogue scale.

Analogue readingLearn itto the nearest half of a division1 °C divisions → 23.5 °C; mm on a ruler → 0.1 cm.Use it when thermometers, rulers, dials.

Zero errorLearn it\(\text{true reading}=\text{reading}-\text{zero reading}\)A meter reading 0.2 N with nothing on it: subtract 0.2 N from every reading.Use it when 'the meter does not read zero'.

Many at onceLearn it\(\text{one}=\dfrac{\text{total for } n}{n}\)Thickness of 1 sheet = stack ÷ number of sheets; period = time for 20 swings ÷ 20.Use it when anything too small or too quick to measure once.

Scale drawingLearn it\(\text{real length}=\text{length on the drawing}\times\text{scale factor}\)A quarter-size drawing: multiply by 4.Use it when 'the diagram is drawn one-quarter full size'.

Tables and calculations: headings, units and significant figures

Column headingLearn itquantity / unite.g. time / s, current / A, 1/I / 1/A. Units never go in the cells.Use it when every table you draw or finish.

Raw readingsLearn itsame number of decimal places down a columnthe precision of the instrument: 5.0, 12.5, 20.0 cmUse it when a column of measurements.

Calculated valuesLearn it2 or 3 significant figures, consistent2.33, 0.175, 12.4 - not 2.333333Use it when any column you calculate.

Unit of a quotientLearn it\(\text{unit of } \dfrac{a}{b}=\dfrac{\text{unit of } a}{\text{unit of } b}\)°C ÷ s → °C/s; N ÷ cm → N/cm; 1 ÷ A → 1/AUse it when rates, gradients, constants.

Mean of repeatsLearn it\(\bar x=\dfrac{x_1+x_2+\dots}{n}\)leave out an anomaly first; give it to the readings' precisionUse it when "calculate the average".

Graphs: axes, best-fit lines, gradients and intercepts

Which way roundLearn it"plot y against x": the FIRST quantity goes up the y-axis"plot V against I": V up, I across.Use it when every graph question.

Good scaleLearn it1, 2 or 5 units per big square (× a power of 10); points fill ≥ half the grid each waynever 3, 6 or 7 per square; never the readings at equal spacing.Use it when choosing scales.

GradientLearn it\(\text{gradient}=\dfrac{\Delta y}{\Delta x}=\dfrac{y_2-y_1}{x_2-x_1}\)triangle at least half the length of the line, points read from the LINE, unit = y unit / x unit.Use it when "determine the gradient".

InterceptLearn it\(y=mx+c\): c is y where x = 0read it only if the x-axis starts at 0; otherwise \(c=y-mx\) from a point on the line.Use it when "the intercept on the y-axis".

ProportionalLearn itstraight line THROUGH THE ORIGINy/x is constant.Use it when "Is y proportional to x?"

Conclusions, errors and improvements

Percentage differenceLearn it\(\dfrac{\text{difference}}{\text{value}}\times100\%\)Compare with 10%. Cambridge uses 10% as the limit of experimental accuracy at this level.Use it when "Are the values equal within the limits of experimental accuracy?"

Within 10% of a known valueLearn itbetween \(0.9\times\) and \(1.1\times\) the valuewithin 10% of 15.0 cm: 13.5 cm to 16.5 cm.Use it when "Does the result agree with the value given?"

Two-part answerLearn itstatement + justification with numbers"Yes: 25.0 and 24.5 differ by 2%, which is within 10%."Use it when every 'support your statement' question.

Proportional from a tableLearn it\(\dfrac{y}{x}\) the same (within 10%) for every rowor a straight line through the origin on a graph.Use it when "Is y proportional to x?"

Variables and planning an investigation

Independent variable (IV)Learn itthe ONE thing you change on purposee.g. diameter of the wireUse it when every plan.

Dependent variable (DV)Learn itthe thing you measuree.g. resistance (from V and I)Use it when every plan.

Control variablesLearn iteverything else that could change the DV - kept the samename it exactly: "the same length of wire", not "length"Use it when "state one variable to keep constant".

ReadingsLearn itat least 5 values of the IV, over a wide sensible range, each repeated and averagedUse it when "how many / which values?"

The plan in orderLearn itapparatus → method (measure DV, change IV) → control → table → conclusionfollow the bullet points in the question, in orderUse it when the planning question.

Mechanics experiments: density, springs, balancing and pendulums

DensityLearn it\(\rho=\dfrac{m}{V}\)g/cm³ from g and cm³.Use it when any density experiment.

Volume by displacementLearn it\(V=V_2-V_1\)water level after − before; object fully under water.Use it when an irregular solid.

ExtensionLearn it\(e=l-l_0\)stretched length − unstretched length.Use it when springs, rubber bands.

Spring constantLearn it\(k=\dfrac{F}{e}\)N/cm or N/m; = gradient of F against e.Use it when springs.

Balancing (moments)Learn it\(m_1d_1=m_2d_2\)clockwise moment = anticlockwise moment about the pivot.Use it when metre rule on a pivot.

PeriodLearn it\(T=\dfrac{t}{n}\)time for n oscillations ÷ n.Use it when pendulums, oscillating springs.

Average speedLearn it\(v=\dfrac{d}{t}\)Use it when ramps, trolleys, rolling balls.

Thermal experiments: cooling, heating and temperature

Temperature changeLearn it\(\Delta\theta=\theta_{\text{start}}-\theta_{\text{end}}\)for cooling, a positive fallUse it when comparing two containers.

Average rate of coolingLearn it\(\dfrac{\Delta\theta}{\Delta t}\)°C/s or °C/min (the sign is usually ignored).Use it when "calculate the average cooling rate".

Electrical energyLearn it\(E=VIt\) (or \(E=Pt\))J from V, A, s.Use it when an electric heater.

Specific heat capacityLearn it\(c=\dfrac{E}{m\,\Delta\theta}\)J/(kg °C); m in kg.Use it when heating a known mass.

Cooling slows downLearn itrate of cooling ∝ (temperature − room temperature), roughlyhot water cools faster than warm waterUse it when "explain why the rate changes".

Optics experiments: ray tracing, blocks and lenses

Law of reflectionLearn it\(i=r\)angles measured from the NORMAL, not from the mirror.Use it when plane mirror ray traces.

Refractive indexLearn it\(n=\dfrac{\sin i}{\sin r}\)given in the question when needed.Use it when refraction through a block.

MagnificationLearn it\(m=\dfrac{\text{image height}}{\text{object height}}\) \(\left(=\dfrac{v}{u}\right)\)no unit.Use it when lens and screen.

Object and image distancesLearn it\(u+v=D\)D = object to screen; u = object to lens; v = lens to screen.Use it when lens experiments.

Lens formula (when given)Learn it\(\dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v}\)use the equation printed in the question.Use it when focal length from u and v.

Electrical experiments: circuits, meters and resistance

ResistanceLearn it\(R=\dfrac{V}{I}\)Ω from V and A.Use it when every circuit question.

Resistance per unit lengthLearn it\(\dfrac{R}{l}\)Ω/cmUse it when a wire on a metre rule.

Series resistorsLearn it\(R=R_1+R_2\)Use it when resistors one after another.

Parallel resistors (two)Learn it\(\dfrac{1}{R}=\dfrac{1}{R_1}+\dfrac{1}{R_2}\)the total is less than eitherUse it when resistors side by side.

MetersLearn itammeter in SERIES · voltmeter in PARALLEL (across the component)Use it when drawing or completing a circuit.

Summary notes

The key points of every note, for a last read before a test.