CIE A Level Physics: Understanding Physical Quantities and SI Units (Chapter 1)

Physical quantity

A quantity that can be measured, consisting of a numerical magnitude and a unit.

Speed

A physical quantity representing the rate of motion, measured in m s-1.

Velocity

A physical quantity that includes both speed and direction.

Volume

A physical quantity representing the amount of space an object occupies, measured in m3.

Potential difference (voltage)

A physical quantity representing the difference in electric potential, measured in volts (V).

Diameter of an atom

Approximately 10−10 m.

Wavelength of UV radiation

Approximately 10 nm.

Height of an adult human

Approximately 2 m.

Speed of sound in air

Approximately 300 m s−1.

Power of a light bulb

Approximately 60 W.

Atmospheric pressure

Approximately 1 × 10^5 Pa.

SI base units

The seven fundamental units from which all other units can be derived.

Mass (SI base unit)

Kilogram (kg).

Length (SI base unit)

Metre (m).

Time (SI base unit)

Second (s).

Current (SI base unit)

Ampere (A).

Temperature (SI base unit)

Kelvin (K).

Newton (N)

The unit of force, defined as kg m s-2.

Joule (J)

The unit of energy, defined as kg m2 s-2.

Pascal (Pa)

The unit of pressure, defined as kg m-1 s-2.

Homogeneity of physical equations

The requirement that the units on both sides of an equation must be the same.

Powers of ten

Numbers achieved by multiplying 10 times itself, used to express very large or very small quantities.

Tera-

Prefix for 10^12.

Giga-

Prefix for 10^9.

Mega-

Prefix for 10^6.

Kilo-

Prefix for 10^3.

Centi-

Prefix for 10−2.

Milli-

Prefix for 10−3.

Micro-

Prefix for 10−6.

Nano-

Prefix for 10−9.

Pico-

Prefix for 10−12.

Known Variables

Quantities provided in a problem statement.

Unknown Variables

Quantities that need to be determined.

Independent Variable

Variable changed in an experiment

Dependent Variable

Variable measured in response

Control Variables

Factors kept constant to ensure valid results.

Resolution of Measuring Equipment

Smallest increment measurable by the device.

Line of Best Fit

Straight line that best represents data points on a graph.

Systematic Errors

Consistent inaccuracies affecting all measurements in the same way.

Random Errors

Variability in measurements due to unpredictable factors.

Parallax Error

Misreading measurement due to viewing angle.

Measurement Uncertainty

Estimated error in measurement values.

Vernier scale

A tool used to measure the extension of the wire with higher precision