Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 1) Physical Quantities, Units & Measurements cover? A: Base quantities, prefixes, conversion strategies, and lab skills for IP Year 3 measurement questions.
Quick recap -- Every measurement must carry a magnitude, a unit, and an honest statement about precision. Know your SI base units, keep prefixes on autopilot, eliminate zero/parallax errors, and present data with significant figures that match your apparatus.
Keep your practice loop tight via our IP Physics tuition hub-it links each topic here to quizzes, diagnostics, and WA-style problem sets.
Base & Derived Quantities
Seven base quantities anchor the SI system. Everything else is built from them.
Base quantity
Symbol
SI unit
Unit symbol
Length
l
metre
m
Mass
m
kilogram
kg
Time
t
second
s
Electric current
I
ampere
A
Thermodynamic temperature
T
kelvin
K
Amount of substance
n
mole
mol
Luminous intensity
Iv
candela
cd
Derived quantities follow from combining base units. Example: force F=ma gives [F]=kg⋅m⋅s−2. Use dimensional homogeneity to check equations: both sides of s=ut+21at2 evaluate to metres, so the relation is dimensionally sound.
Prefixes & Scientific Notation
Memorise the common prefixes so you can convert without reaching for a calculator.
Prefix
Symbol
Factor
giga
G
109
mega
M
106
kilo
k
103
centi
c
10−2
milli
m
10−3
micro
μ
10−6
nano
n
10−9
Switch comfortably between standard notation and scientific notation N×10n where 1≤N<10. Large: 5.6×103m. Small: 4.5×10−3s. The coefficient's significant figures carry the precision--3.450×104 shows four significant figures, for instance.
Precision, Accuracy & Error Types
Precision is about spread. Tight clustering of repeated readings = precise instrument/technique.
Accuracy is about truth. Consistently hitting the accepted value = accurate measurement.
Random errors (parallax, background fluctuations) scatter readings both above and below the true value. Average repeated trials to tame them.
Systematic errors (zero error, miscalibrated apparatus) bias readings in one direction. Detect and correct using calibration checks or offset adjustments.
Significant Figures & Decimal Places
Report raw readings with all digits the instrument provides; state processed values with the limiting significant figures of the inputs.
Non-zero digits are significant; zeros between significant digits count; trailing zeros count only when a decimal point is shown.
Decimal places describe formatting; significant figures communicate precision. A balance reading 12.30 g has 4 s.f. and 2 d.p.
When multiplying/dividing, round the final answer to the smallest number of significant figures used. When adding/subtracting, match the least precise decimal place.
Converting Units Systematically
Write the starting value with its unit, e.g. 3.6m.
Multiply by conversion fractions that equal one, e.g. 1000mm/1m.
Cancel units algebraically; the numbers follow the same multiplication.
Express the answer with the same significant figures as the original measurement.
Example: 3.6m×1m100cm=3.6×102cm.
Measuring Length & Time Reliably
Common errors
Parallax error: reading a scale from an angle. Fix: align your eye perpendicular to the scale; use mirrored scales when available.
Zero error: instrument does not read zero when it should. Fix: record the offset and subtract/add it during processing.
Typical apparatus
Meter rule: minimum uncertainty ±0.1cm. Read at eye level.
Vernier calipers: resolution 0.01cm. If the jaws show +0.02cm when closed, subtract 0.02 cm from all readings.
Micrometer screw gauge: resolution 0.01mm. Watch for positive/negative zero error the same way.
Stopwatch / light gate: for intervals under a second, repeat runs and average to reduce reaction-time error; for pendulum timing, measure multiple oscillations and divide.
Recording, Processing & Presenting Data
Layout tables with headings that include units (e.g. Time/s). Keep consistent decimal places within a column.
When calculating derived values (e.g. v=ts), propagate significant figures appropriately.
Graphs: choose sensible scales, label axes with quantity and unit, plot using the largest portion of the grid, draw a best-fit line through the scatter, and use large triangles to determine gradient.
Quote gradients/intercepts with the same precision as the data that produced them. Attach units to gradients (e.g. N⋅m−1).
Precautions & Improvements
Secure the apparatus (clamps, retort stands) to prevent drift during readings.
Repeat measurements and look for outliers before averaging.
For time-based experiments, start/stop at a consistent marker; for oscillations, time 10 cyles or more.
Document ambient conditions (room temperature, zeroed instruments) so you can justify improvements when writing evaluations.
Mastering these fundamentals pays off in every later topic. The sooner you automate unit checks, prefix conversions, and data presentation habits, the more headspace you'll have for advanced mechanics and electromagnetism.
Practice Quiz
Put your measurement fluency to the test with mixed MCQs and structured responses covering base units, significant figures, calibration, and uncertainty propagation.
