Title: InkPhysics / Measurements
On every note of this deck, unless a note says otherwise:
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Front: DEFINITION
Define: Reproducibility.
Back: A different experimenter, or a different method or equipment, still obtains consistent results.

Front: DEFINITION
Define: Random error.
Back: Error that scatters readings unpredictably either side of the true value; reduced by repeating and averaging.

Front: DEFINITION
Define: Repeatability.
Back: The same experimenter, using the same method and equipment, obtains consistent results.

Front: DEFINITION
Define: Precision.
Back: How closely repeated readings cluster together; a precise result need not be accurate.

Front: EQUATION — NOT ON THE DATA SHEET
Percentage uncertainty:
percentage uncertainty = ?
Back: percentage uncertainty = uncertaintyvalue × 100

Front: CHECK YOURSELF
A wire's diameter is measured as 0.40 ± 0.01 mm. What is the percentage uncertainty in its cross-sectional area?
Show a hint
Area depends on the diameter squared. What does the power rule do to a percentage uncertainty?
Back: Percentage uncertainty in the diameter: (0.01 / 0.40) × 100 = 2.5%.
The area goes as d^2, so the power rule doubles it: the area is uncertain by 5%.
Working through the radius changes nothing: halving a value halves its absolute uncertainty too, so the percentage uncertainty is untouched.

Front: DEFINITION
Define: Resolution.
Back: The smallest change in a quantity that an instrument can display.

Front: DEFINITION
Define: Order of magnitude.
Back: A value expressed to the nearest power of ten.

Front: DEFINITION
Define: SI base quantities.
Back: The quantities from which all others at A-level are built: mass (kg), length (m), time (s), electric current (A), temperature (K) and amount of substance (mol).

Front: DEFINITION
Define: Uncertainty.
Back: The interval within which the true value can reasonably be expected to lie, quoted after a ± sign.

Front: CHECK YOURSELF
Estimate, to the nearest order of magnitude, the energy needed to climb one flight of stairs.
Show a hint
The force is your weight. Take g as 10 and a flight as about 3 m.
Back: Weight of a person: about 70 kg × 10 = 700 N. Height of a flight: about 3 m.
Energy = force × distance ≈ 700 × 3 = 2100 J, so the order of magnitude is 10^3 J, a couple of kilojoules.
The exact answer depends on the person and the staircase, and that is fine. Anyone whose calculation of this quantity produces 10^6 J has found an error, not a big staircase.

Front: DEFINITION
Define: Systematic error.
Back: Error that shifts every reading the same way, such as a zero error; repeating does not reduce it.

Front: DEFINITION
Define: Accuracy.
Back: How close a result is to the true value.

Front: CHECK YOURSELF
(a) Write 250 μm in metres, in standard form. (b) An electron has 5.0 keV of kinetic energy. How many joules is that?
Show a hint
Take one prefix at a time: micro first, then kilo, then the eV to J factor.
Back: (a) Micro means 10^−6, so 250 μm = 250 × 10^−6 m = 2.5 × 10^−4 m.
(b) 5.0 keV = 5.0 × 10^3 eV. Each eV is 1.60 × 10^−19 J, so the energy is 5.0 × 10^3 × 1.60 × 10^−19 = 8.0 × 10^−16 J.