Measurements, quantities and uncertainty: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Physics Topic 1, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
One of the seven units all others derive from: metre, kilogram, second, ampere, kelvin, mole and candela.
Homogeneity of equations
Both sides must have identical base units. A homogeneous equation may still be wrong, but a non-homogeneous one is definitely wrong.
Scalar vs vector
Scalars have magnitude only (speed, energy, mass); vectors have magnitude and direction (velocity, force, momentum) and must be resolved.
Resolving a vector
Splitting a vector into perpendicular components: the horizontal is Fcos(theta), the vertical Fsin(theta) for an angle to the horizontal.
Random error
Scatters readings either side of the true value. Reduced by repeating measurements and averaging.
Systematic error
Shifts every reading the same way, often from a zero error or miscalibration. Repeating does not reduce it.
Precision vs accuracy
Precise readings cluster closely together; accurate readings sit near the true value. Measurements can be precise yet badly inaccurate.
Absolute vs percentage uncertainty
Absolute carries the unit of the measurement; percentage is that divided by the value. Percentages add when quantities are multiplied or divided.
Combining uncertainties
Add absolute uncertainties when adding or subtracting; add percentage uncertainties when multiplying or dividing; multiply by the power when raising to a power.
Error bars
Show the uncertainty range of each plotted point. The gradient uncertainty is found from the steepest and shallowest lines that still pass through them.
Estimating an order of magnitude
Rounding quantities to the nearest power of ten to check whether an answer is physically plausible.
Vernier scale
Gives a reading finer than the main scale by using slightly offset divisions, typically resolving to 0.1 millimetres or better.
Significant figures in answers
Quote to the same number as the least precise measurement used. Extra digits imply a precision the data does not support.
Micrometer zero error
A systematic offset when the jaws are closed. Subtract it from every reading rather than repeating the measurement.
Straight-line graph form
Rearranging an equation into y equals mx plus c lets gradient and intercept give the physical constants directly.
Anomalous result
A point far from the trend. Investigate and, if a cause is found, exclude it — never simply delete inconvenient data.