IB MYP 4-5 Physics- SI units and standard prefixes- Study Notes - New Syllabus
IB MYP 4-5 Physics- SI units and standard prefixes- Study Notes
Key Concepts
- SI Units, Prefixes & Conversion
SI Units, Prefixes & Conversion
SI Units
SI (Système International) Units are the globally accepted standard units used in scientific measurements. Each physical quantity has a base SI unit.
- 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)
Derived SI Units (with examples)
Derived units are formed by combining base units using multiplication or division.
- Velocity: \( \text{m/s} \)
- Acceleration: \( \text{m/s}^2 \)
- Force (Newton, N): \( \text{kg·m/s}^2 \)
- Energy (Joule, J): \( \text{kg·m}^2/\text{s}^2 \)
- Power (Watt, W): \( \text{kg·m}^2/\text{s}^3 \)
Standard SI Prefixes
Prefixes are used to express very large or very small quantities more conveniently. They are powers of 10 applied to SI units.
| Prefix | Symbol | Factor | Scientific Notation |
|---|---|---|---|
| tera | T | \( 1\,000\,000\,000\,000 \) | \( 10^{12} \) |
| giga | G | \( 1\,000\,000\,000 \) | \( 10^9 \) |
| mega | M | \( 1\,000\,000 \) | \( 10^6 \) |
| kilo | k | \( 1\,000 \) | \( 10^3 \) |
| centi | c | \( 0.01 \) | \( 10^{-2} \) |
| milli | m | \( 0.001 \) | \( 10^{-3} \) |
| micro | \( \mu \) | \( 0.000001 \) | \( 10^{-6} \) |
| nano | n | \( 0.000000001 \) | \( 10^{-9} \) |
| pico | p | \( 0.000000000001 \) | \( 10^{-12} \) |
Unit Conversion
Unit conversion is the process of changing a quantity from one unit to another using multiplication or division by a conversion factor.
- Use prefix values or known conversion factors between units.
- Make sure units cancel appropriately when multiplying/dividing.
- Always express the final answer in the desired unit with proper SI formatting.
Common conversions using prefixes:
- \( 1\,\text{km} = 1000\,\text{m} = 10^3\,\text{m} \)
- \( 1\,\text{cm} = 0.01\,\text{m} = 10^{-2}\,\text{m} \)
- \( 1\,\text{mg} = 0.001\,\text{g} = 10^{-6}\,\text{kg} \)
- \( 1\,\mu\text{s} = 10^{-6}\,\text{s} \)
To convert from one prefix to another, subtract the powers of 10 and move the decimal accordingly.
Example:
Convert a mass of \( 3.5\,\text{kg} \) to grams.
▶️ Answer/Explanation
\( 1\,\text{kg} = 1000\,\text{g} \)
So, \( 3.5\,\text{kg} = 3.5 \times 1000 = 3500\,\text{g} \)
Final Answer: \( \boxed{3500\,\text{g}} \)
Example:
Convert a distance of \( 250\,\text{cm} \) to metres using SI prefixes.
▶️ Answer/Explanation
\( 1\,\text{cm} = 10^{-2}\,\text{m} \)
\( 250\,\text{cm} = 250 \times 10^{-2} = 2.5\,\text{m} \)
Final Answer: \( \boxed{2.5\,\text{m}} \)
Example:
Express a time of \( 0.000003\,\text{s} \) in microseconds using an appropriate SI prefix.
▶️ Answer/Explanation
\( 1\,\mu\text{s} = 10^{-6}\,\text{s} \)
\( 0.000003\,\text{s} = 3 \times 10^{-6}\,\text{s} = 3\,\mu\text{s} \)
Final Answer: \( \boxed{3\,\mu\text{s}} \)
Example:
An electric current of \( 0.005\,\text{A} \) flows through a circuit. Express it in milliamperes (mA).
▶️ Answer/Explanation
\( 1\,\text{mA} = 10^{-3}\,\text{A} \)
\( 0.005\,\text{A} = \dfrac{0.005}{10^{-3}} = 5\,\text{mA} \)
Final Answer: \( \boxed{5\,\text{mA}} \)