A physical quantity needs both a number and a unit
A numerical value is meaningful only alongside its unit. Estimating the expected scale before calculating can reveal a missed prefix or an implausible result.
Follow the reasoning
- State the quantity being measured or calculated.
- Choose or convert to a consistent unit.
- Compare the result with an estimate of a realistic scale.
Try it in a past paper 4
Open the question, then use its mark scheme to check your work.
Question 9
Interpret the giga prefix in a material’s modulus.
Build the supporting skills. Practise SI units before exploring this connection. This question has not been checked as a combined example of the connection.
Question 1
Identify an SI base unit.
Build the supporting skills. Practise Physical quantities and SI units before exploring this connection. This question has not been checked as a combined example of the connection.
Question 8
Describe electron diffraction and compare the de Broglie wavelengths of electrons and a car.
Build the supporting skills. Practise Physical quantities and SI units before exploring this connection. This question has not been checked as a combined example of the connection.
Question 1
Estimate a microwave wavelength and recognise its scale.
Build the supporting skills. Practise Physical quantities before exploring this connection. This question has not been checked as a combined example of the connection.
A curated collection checked against the question papers and mark schemes; not a complete past-paper catalogue. Links open official OCR PDFs in a new tab.
Put the ideas to work
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Specification outcomes (5)
- 2.1.1(a) Physical quantities have a numerical value and a unit.
- 2.1.1(b) Make estimates of physical quantities listed in the specification.
- 2.1.2(a) Système Internationale (S.I.) base quantities and their units – mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol).
- 2.1.2(b) Derived units of S.I. base units, such as momentum (kg m s⁻¹) and density (kg m⁻³).
- 2.1.2(e) Use prefixes and their symbols to indicate decimal submultiples or multiples of units (pico, nano, micro, milli, centi, deci, kilo, mega, giga, tera).