AS Level Physics: Physical Quantities, SI Units, and Uncertainties

Flashcards covering key definitions, SI base units, prefixes, errors, uncertainties, and scalar versus vector quantities from past exam paper problems.

Scalar quantity

A physical quantity that is completely specified by its magnitude and unit alone, having no direction.

Vector quantity

A physical quantity that is not completely specified by its magnitude and unit alone, requiring a direction to be fully defined.

Density

The ratio of mass to volume for any object, given by the relation $\rho = \frac{M}{V}$.

Systematic error

An error that shifts all measurements in a consistent direction by the same amount, often caused by an incorrectly calibrated instrument or zero error, and whose effect cannot be reduced by repeating and averaging measurements.

Zero error

A specific type of systematic error where a measuring instrument displays a non-zero value when the true value being measured is zero.

Accuracy

The degree of closeness of a measured value to the true or accepted reference value of the quantity being measured.

Precision

The closeness of agreement among repeated measurements or readings, often reflected by the smallest scale division or number of decimal places of the measuring instrument.

Volt ($\text{V}$) in SI base units

$\text{kg}\,\text{m}^2\,\text{s}^{-3}\,\text{A}^{-1}$, determined from electric potential being work done per unit charge ($V = \frac{W}{Q}$).

Spring constant ($k$) in SI base units

$\text{kg}\,\text{s}^{-2}$, derived from force per unit extension ($k = \frac{F}{e}$).

Moment of a force in SI base units

$\text{kg}\,\text{m}^2\,\text{s}^{-2}$, derived from the product of force and perpendicular distance ($\text{Moment} = F \times d$).

Coulomb's law constant ($k$) in SI base units

$\text{kg}\,\text{m}^3\,\text{s}^{-4}\,\text{A}^{-2}$, derived from the electrostatic force equation $F = \frac{k q_1 q_2}{r^2}$.

Kelvin ($\text{K}$)

The SI base unit of thermodynamic temperature.

Tera ($\text{T}$)

A metric prefix representing a power-of-ten multiple of $10^{12}$.

Nano ($\text{n}$)

A metric prefix representing a power-of-ten submultiple of $10^{-9}$.

Micro ($\mu$)

A metric prefix representing a power-of-ten submultiple of $10^{-6}$.

Pico ($\text{p}$)

A metric prefix representing a power-of-ten submultiple of $10^{-12}$.

Fractional uncertainty in $\frac{X}{Y^2}$

$x + 2y$, where $x$ is the fractional uncertainty in quantity $X$ and $y$ is the fractional uncertainty in quantity $Y$.

Vernier caliper

An instrument suitable for measuring lengths of around $0.12\,\text{m}$ to an absolute uncertainty of $\pm 0.0001\,\text{m}$ ($\pm 0.1\,\text{mm}$).

Power

A scalar quantity defined as the rate at which work is done or energy is transferred.

Momentum

A vector quantity defined as the product of the mass and velocity of an object.