What is a systematic error?

A systematic error is an error that causes all measurements to be shifted in the same direction from the true value by a consistent amount.

A zero error is a type of systematic error where an instrument does not read zero when it should.

If a balance consistently reads 0.5 g when empty, what type of error is this?

This is a zero error, which is a type of systematic error.

Can systematic errors be reduced by repeating measurements and calculating an average?

No, systematic errors cannot be reduced by repeating measurements and averaging because they shift all readings by the same amount in the same direction.

What are random errors?

Random errors are errors that cause measurements to scatter unpredictably above and below the true value.

OCR A-Level Physics A H556

Practical Skills in the Written Papers

Topic overview Planning an experiment Implementing and recording Processing and interpreting data Plotting and interpreting graphs Evaluating results and procedures Mathematical skills and notation

The Practical Endorsement

Topic overview Analogue and digital measuring instruments Improving accuracy with repeat timing, fiducial markers and plumb lines Timing, calipers and micrometers Constructing and testing circuits Signal generators and oscilloscopes Generating and measuring waves Data loggers, modelling software and ionising radiation

Physical Quantities and Units

Topic overview Physical quantities, estimation and unit conversions S.I. base and derived units Prefixes, homogeneity and labelling conventions

Making Measurements and Analysing Data

Topic overview Systematic and random errors Precision, accuracy and uncertainties

Nature of Quantities

Topic overview Scalars and vectors Adding and resolving vectors

Motion

Topic overview Displacement, speed, velocity and acceleration Motion graphs and the equations of motion Measuring g and investigating motion experimentally Free fall, reaction time and stopping distance Projectile motion

Forces in Action

Topic overview Newton's second law and weight Drag and the factors affecting it Terminal velocity Moments, couples and equilibrium Density, pressure and upthrust

Work, Energy and Power

Topic overview Work done and conservation of energy Kinetic and gravitational potential energy Power and efficiency

Materials

Topic overview Hooke's law and springs Force-extension graphs and work done Elastic potential energy, stress and strain The Young modulus Stress-strain graphs and material behaviour

Newton’s Laws of Motion and Momentum

Topic overview Newton's three laws and linear momentum Force as rate of change of momentum Impulse and force-time graphs Conservation of momentum and collisions

Charge and Current

Topic overview Electric current and the coulomb Elementary charge, charge carriers and Kirchhoff's first law Mean drift velocity

Energy, Power and Resistance

Topic overview Circuit symbols and diagrams Potential difference and e.m.f.Energy transfer in circuits Ohm's law and I-V characteristics Filament lamps, diodes, thermistors and LDRs Resistivity and how it is measured How resistivity varies with temperature Electrical power and the kilowatt-hour

Electrical Circuits

Topic overview Kirchhoff's laws and combining resistances E.m.f., internal resistance and lost volts Potential dividers

Waves

Topic overview Progressive waves and their properties The wave equation Reflection, refraction and diffraction Wave graphs and intensity The electromagnetic spectrum Polarisation Refraction and refractive index Critical angle and total internal reflection The principle of superposition Interference, coherence and path difference Two-source interference, Young's double-slit experiment and the diffraction grating Forming stationary waves Stationary waves on strings and in air columns Measuring the speed of sound Node spacing, amplitude and phase in stationary waves Harmonics and the fundamental mode

Quantum Physics

Topic overview Photons, electronvolts and the Planck constant from LEDs Demonstrating the photoelectric effect Work function and Einstein's equation Electron diffraction The de Broglie equation

Thermal Physics

Topic overview Thermal equilibrium and absolute temperature The kinetic model of solids, liquids and gases Brownian motion and internal energy Specific heat capacity Measuring specific heat capacity Specific latent heat Measuring specific latent heat Moles, the Avogadro constant and kinetic theory Gas laws, the ideal gas equation and r.m.s. speed Maxwell-Boltzmann distribution, Boltzmann constant and internal energy

Circular Motion

Topic overview Radians, angular velocity and period Centripetal force and acceleration

Oscillations

Topic overview Describing simple harmonic motion The defining equation of simple harmonic motion and timing oscillations Velocity, period and graphical relationships Energy in a simple harmonic oscillator Damping, forced oscillations and resonance

Gravitational Fields

Topic overview Gravitational fields and field strength Newton's law of gravitation Field strength of a point mass and the uniform field near Earth Kepler's laws and orbital motion Orbital period and geostationary orbits Gravitational potential Gravitational potential energy and escape velocity

Astrophysics and Cosmology

Topic overview The solar system and the birth of a star The death of a low-mass star Supernovae, neutron stars and black holes The Hertzsprung-Russell diagram Energy levels and emission spectra Absorption spectra and spectral lines Photon energy and the diffraction grating Wien's law and Stefan's law Astronomical distances, parallax and the cosmological principle Doppler shift and Hubble's law The expanding universe and the Big Bang Evidence for the Big Bang and dark energy

Capacitors

Topic overview Capacitance and charging a capacitor Capacitors in series Capacitors in parallel and combined circuits Energy stored by a capacitor Charging and discharging through a resistor Investigating capacitor discharge The time constant Iterative modelling, exponential decay and the constant-ratio property

Electric Fields

Topic overview Electric fields and field lines Coulomb's law and electric field strength Uniform fields, parallel plates and permittivity Electric potential Electric potential energy and capacitance of a sphere

Electromagnetism

Topic overview Magnetic fields and field patterns Fleming's left-hand rule and the motor effect Magnetic flux density and the tesla Charged particles in magnetic fields Magnetic flux, flux linkage and Faraday's law Transformers and the a.c. generator

Nuclear and Particle Physics

Topic overview Alpha-particle scattering and the nuclear model Proton number, nucleon number and isotopes The strong nuclear force and nuclear radius Particles, antiparticles and hadrons Leptons and the quark model Quark composition and charges Beta decay in the quark model Radioactive decay and the three radiations Nuclear decay equations Activity, decay constant and half-life Exponential decay and radioactive dating Mass-energy equivalence Annihilation, mass defect and binding energy Binding energy per nucleon and induced fission The fission reactor and nuclear waste Nuclear fusion and balancing nuclear equations

Medical Imaging

Topic overview The X-ray tube X-ray attenuation and imaging CAT scanning Medical tracers and the gamma camera PET scanning Ultrasound and the piezoelectric transducer Acoustic impedance and reflection Doppler ultrasound

Making Measurements and Analysing Data

2 subtopics
6 things to know
All three papers

What Making Measurements and Analysing Data covers

The treatment of error and uncertainty: what distinguishes a systematic error from a random one, and how uncertainty is expressed, combined and shown on a graph.

Where it is assessed

All three papers

Practical skills and physical quantities, assumed throughout.

Check the OCR specification ↗

The 2 subtopics

Each one has its own page.

What you need to know

Answer each one before you reveal it.

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Evaluation

How is percentage uncertainty calculated from absolute uncertainty, and how are percentage uncertainties combined when quantities are multiplied or divided, or when a quantity is raised to a power n?

Evaluation

Define a worst line on a graph, and state how it is used to find the uncertainty in the gradient.

Evaluation

In what units are absolute and percentage uncertainties expressed, and how are uncertainties combined when quantities are added or subtracted?

Evaluation

Which type of error affects precision, and which affects accuracy?

Key term

Define a zero error.

Key term

Why does repeating measurements and averaging help reduce random errors but not systematic errors?

Take Making Measurements and Analysing Data further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

Systematic error vs Random error
Systematic error: an error that shifts every reading in the same direction by the same amount. Random error: an unpredictable scatter that repeating and averaging can reduce.
Accuracy vs Precision
Accuracy: how close a measurement lies to the true value. Precision: how closely repeated measurements agree with one another.
Absolute uncertainty vs Percentage uncertainty
Absolute uncertainty: the uncertainty expressed in the same unit as the measurement. Percentage uncertainty: the uncertainty expressed as a proportion of the measurement.

Questions from this topic

Each one with the model answer underneath.

1
What is a systematic error?
Model answer
A systematic error is an error that causes all measurements to be shifted in the same direction from the true value by a consistent amount.
2
Define a zero error.
Model answer
A zero error is a type of systematic error where an instrument does not read zero when it should.
3
If a balance consistently reads 0.5 g when empty, what type of error is this?
Model answer
This is a zero error, which is a type of systematic error.
4
Can systematic errors be reduced by repeating measurements and calculating an average?
Model answer
No, systematic errors cannot be reduced by repeating measurements and averaging because they shift all readings by the same amount in the same direction.
5
Why does repeating measurements and averaging help reduce random errors but not systematic errors?
Model answer
Random errors scatter unpredictably above and below the true value, so averaging cancels them out. Systematic errors shift all readings in the same direction, so averaging does not eliminate them.
6
What are random errors?
Model answer
Random errors are errors that cause measurements to scatter unpredictably above and below the true value.

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Making Measurements and Analysing Data revision questions

What does Making Measurements and Analysing Data cover in OCR A-Level Physics A?: 2 subtopics: systematic and random errors and precision, accuracy and uncertainties. Each one has its own page with questions and model answers.
How is Making Measurements and Analysing Data organised?: By the OCR H556 specification, subtopic by subtopic, so it matches the order you are taught it in.

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