Lesson 1 of 4 · Grade 10 Physics
Measurement and SI units
15 min
Basic SI units
- Length: metre (m)
- Mass: kilogram (kg)
- Time: second (s)
- Electric current: ampere (A)
- Temperature: kelvin (K)
- Amount of substance: mole (mol)
- Luminous intensity: candela (cd)
Prefixes
kilo (k) = 10³, centi (c) = 10⁻², milli (m) = 10⁻³, micro (µ) = 10⁻⁶, mega (M) = 10⁶.
Instruments
- Metre rule: accuracy 0.1 cm.
- Vernier calipers: accuracy 0.01 cm; for diameters and thicknesses.
- Micrometer screw gauge: accuracy 0.01 mm; for very small diameters like wires.
- Beam balance: measures mass. Spring balance: measures weight (force).
Density
Density = mass ÷ volume (kg/m³ or g/cm³).
A stone of mass 120 g displaces 40 cm³ of water: density = 120 ÷ 40 = 3 g/cm³. Water has a density of 1 g/cm³ (1,000 kg/m³).
Key points to remember
- SI units: m, kg, s, A, K, mol, cd
- Micrometer screw gauge reads to 0.01 mm
- Density = mass ÷ volume
- Water density = 1 g/cm³
Test yourself
