Understanding base quantities and derived quantities

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Malaysia SPM Form 4, Chapter 1: Introduction to Physics
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Contents 1 Physical Quantities 1.1 Base Quantities 1.2 Derived Quantities 2 Standard Form 3 Prefixes 4 Expressing Derived Quantities and Their Units in Terms of Base Quantities and Base Units 5 Solving Problems Involving Conversion of Units 6 Frequenly Asked Question 7 Additional notes 8 External Links

Physical Quantities

1. A physical quantity is a quantity that can be measured.
2. A physical quantity can be divided into base quantity and derived quantity.

Base Quantities

1. Base quantities are the quantities that are conventionally accepted as functionally independent of one another.
2. It is a quantity that cannot be defined in term of other physical quantity.
3. The base quantities and its units are as in the table below:

The Base Quantities

Quantity	Name of unit	Unit symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Thermodynamic temperature	Kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

[Notes: Amount of substance and Luminous intensity are not discussed in SPM physics syllabus.]

Derived Quantities

A derived quantity is a Physics quantity that is not a base quantity. It is the quantities which derived from the base quantities through multiplying and/or dividing them.

Derived Unit
The derived unit is a combination of base units through multiplying and/or dividing them.

Standard Form

Prefixes

Prefixes are the preceding factor used to represent very small and very large physical quantities in SI units.

Conversion of prefixes

Prefixes to Normal Number

Example 1

The frequency of the radio wave is 350M Hz. What is the frequency of the radio wave in Hz? Answer Mega (M) = 1,000,000 or 106 Therefore, 350MHz = 250 x 106Hz

Example 2

The thickness of a film is 25nm. What is the thickness in unit meter? Answer nano (n) = 0.000000001 or 10-9 Therefore 25nm = 25 x 10-9nm

Normal number to Prefixes

Example 3

0.255 s is equal to how many ms. Answer mili (m) = 0.001 or 10-3 To write a normal number with prefixes, we divide the number with the value of the prefixes 0.0255 s = 0.0255 ÷ 10-3 = 25.5 ms

Example 4

Convert 265,500,000 W into GW. Answer Gega (G) = 1,000,000,000 or 109 Therefore 265,500,000 W = 265,500,000 ÷ 109 = 0.2655GW

Expressing Derived Quantities and Their Units in Terms of Base Quantities and Base Units

Solving Problems Involving Conversion of Units

Frequenly Asked Question

Additional notes

[Additional notes content information relates to this topic but may not be in the SPM syllabus]

External Links

NIST: Physical Quantity Technick Physchem Learn Physics Today Physchem