A level Physics 2020-21 - Induction Work - Physical Quantities - Significant Figures

Q: What are the differences between base units and derived units in SI?

Base units are the seven fundamental quantities defined by SI. Derived units are formed by multiplying or dividing base units and sometimes use simpler named units or equivalent notation.

Q: Why do physics values use units and unit prefixes?

Numbers represent measurable physical quantities, and units give them meaning. Prefixes help write very large or very small values more compactly.

Q: How do significant figures affect answers in physics calculations?

Calculated results must be rounded to the same number of significant figures as the least precise data used in the formula.

Sep 5, 2026

Upload by Riley West

Induction work for A level Physics 2020-21 focused on foundational measurement skills. It explains physical quantities and the distinction between base and derived units using SI, including unit symbols, derived notation, standard form, and unit conversions for comparisons. The material then introduces significant figures, detailing which digits count as significant, how precision is represented, and how calculations must be rounded to match the least precise input. Practice questions support unit expression and precision handling.

LanguageEnglish

CategoryExam

FormatPDF

Pages14

Reading Time35 min

AccessFree to download

1. Physical Quantities

Base units

Derived units

Unit prefixes and standard form

Unit conversion examples

Practice questions

2. Significant Figures

Rules for significant figures

Examples and interpretation

Significant figures in calculations

Practice questions

A level Physics 2020-21 INDUCTION WORK Student Class 12 Form SGS 2020 1. Physical Quantities Maths and Physics have an important but overlooked distinction by students. Numbers in Physics have meaning – they are the size of physical quantities which exist. To give numbers meaning we suffix them with units. There are two types of units: Base units These are the seven fundamental quantities defined by the Système international d’Unités (SI units) . Once defined, we can make measurements using the correct unit and make comparisons between values. | Basic quantity | Unit | | | --- | --- | --- | | | Name | Symbol | | Mass | kilogram | kg | | Length | metre | m | | Time | second | s | | Current | ampere | A | | Temperature | kelvin | K | | Amount of substance | mole | mol | | Luminous intensity | candela | cd | Derived units These are obtained by multiplying or dividing base units. Some derived units are complicated and are given simpler names, such as the unit of power Watt (W) which in SI units would be m2 kgs-3. Notice that at A-Level we use the equivalent notation ms-1 rather than m/s. Do not become confused between the symbol we give to the quantity itself, and the symbol we give to the unit. For some examples, see the table on the right. Often the value of the quantity we are interested in is very big or small. To save space and simplify these numbers, we prefix the units with a set of symbols. Knowledge of standard form and how to input it into your calculator is essential. For example: 245 x 10-12 m = 245 pm 2.45 x 103 m = 2.45 km We may need to convert units to make comparisons. For example: Which is bigger, 0.167 GW or 1500 MW? 0.167 GW = 0.167 x109 W = 167 x106 W = 167 MW < 1500 MW | Derived quantity | Unit | | | --- | --- | --- | | | Name | Symbols | | Volume | cubic metre | m3 | | Velocity | metre per second | ms-1 | | Density | kilogram per cubic metre | kgm-3 | | Quantity | Quantity symbol | Unit name | Unit symbols | | --- | --- | --- | --- | | Length | L or l or h or d or s | metre | m | | Wavelength | λ | metre | m | | Mass | m or M | kilogram | kg | | Time | t | second | s | | Temperature | T | kelvin | K | | Charge | Q | coulomb | C | | Momentum | p | kilogram metres per second | kg ms-1 | | Prefix | Symbol | Name | Multiplier | | --- | --- | --- | --- | | femto | f | quadrillionth | 10-15 | | pico | p | trillionth | 10-12 | | nano | n | billionth | 10-9 | | micro | µ | millionth | 10-6 | | milli | m | thousandth | 10-3 | | centi | c | hundredth | 10-2 | | kilo | k | thousand | 103 | | mega | M | million | 106 | | giga | G | billion | 109 | | tera | T | trillion | 1012 | | peta | P | quadrillion | 1015 | Physical Quantities-Questions 1) The unit of energy is the joule. Find out what this unit is expressed in terms of the base SI units. 2) Convert these numbers into normal form: a) 5.239 x 103 b) 4.543 x 104 c) 9.382 x 102 d) 6.665 x 10-6 3) Convert these quantities into standard form: a) 65345 N b) 765 s c) 486856 W d) 0.987 cm2 e) 1.951 x 10-2 f) 1.905 x 105 g) 6.005 x 103 e) 0.000567 F f) 0.0000605 C g) 0.03000045 J 4) Write down the solutions to these problems, giving your answer in standard form: a) (3 .45 x 10-5 + 9.5 x 10-6) ÷ 0.0024 b) 2.31 x 105 x 3.98 x 10-3 + 0.0013 5) Calculate the following: a) 20mm in metres b) 3.5kg in grams c) 589000 μm in metres d) 1m2 in cm2 (careful) e) 38 cm2 in m2 6) Find the following: a) 365 days in seconds, written in standard form b) 3.0 x 104 g written in kg c) 2.1 x 106 Ω written in MΩ d) 5.9 x 10-7 m written in μm e) Which is bigger? 1452 pF or 0.234 nF Mark = /27 2. Significant Figures Number in Physics also show us how certain we are of a value. How sure are you that the width of this page is 210.30145 mm across? Using a ruler you could not be this precise. You would be more correct to state it as being 210 mm across, since

FAQs

What are the differences between base units and derived units in SI?

Base units are the seven fundamental quantities defined by SI. Derived units are formed by multiplying or dividing base units and sometimes use simpler named units or equivalent notation.

Why do physics values use units and unit prefixes?

Numbers represent measurable physical quantities, and units give them meaning. Prefixes help write very large or very small values more compactly.

How do significant figures affect answers in physics calculations?

Calculated results must be rounded to the same number of significant figures as the least precise data used in the formula.

Sep 5, 2026

Upload by Riley West