State the five SI base quantities required for this course and their base units.

mass — kilogram (kg) length — metre (m) time — second (s) current — ampere (A) temperature — kelvin (K)

Define a derived unit .

A derived unit is a unit that can be written as a combination of the SI base units (e.g. the joule or the pascal).

True or False? The newton is an SI base unit.

False. The newton is a derived unit ; in SI base units it is written as kg m s -2 .

Define a homogeneous physical equation.

A homogeneous physical equation is one in which the combined base units on both sides of the equation are the same .

How can you check whether a physical equation is homogeneous?

Reduce both sides of the equation to their SI base units and check they are equal . If they do not match, the equation cannot be correct.

What does it mean for a quantity to be dimensionless ?

It has no units — its combined base units cancel to leave a value of 1 (for example, γ in the speed-of-sound equation).

State the symbols and powers of ten for the prefixes tera, giga, mega and kilo.

tera (T) = 10 12 giga (G) = 10 9 mega (M) = 10 6 kilo (k) = 10 3

The prefix milli (m) represents a factor of .......... .

The prefix milli (m) represents a factor of 10 -3 .

True or False? The prefix micro (μ) represents a factor of 10 -9 .

False. The prefix micro (μ) represents 10 -6 ; the factor 10 -9 is nano (n).

An equation has base units of kg m s -2 on one side and kg m 2 s -2 on the other. Is it homogeneous?

No. The base units on each side are different , so the equation is not homogeneous and cannot be physically correct.

A LevelPhysicsCambridge (CIE)Flashcards1. Physical Quantities & UnitsSI Units

SI Units (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontSI Units
State the five SI base quantities required for this course and their base units.
BackSI Units
mass — kilogram (kg)
length — metre (m)
time — second (s)
current — ampere (A)
temperature — kelvin (K)
BackSI Units
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Cards in this collection (13)

State the five SI base quantities required for this course and their base units.
- mass — kilogram (kg)
- length — metre (m)
- time — second (s)
- current — ampere (A)
- temperature — kelvin (K)
Define a derived unit.
A derived unit is a unit that can be written as a combination of the SI base units (e.g. the joule or the pascal).
Express the newton (N) in SI base units.
From $F = m a$ :
$N = {kg m s}^{- 2}$
Express the joule (J) in SI base units.
From $E_{k} = \frac{1}{2} m v^{2}$ :
$J = {kg m}^{2} s^{- 2}$
Express the pascal (Pa) in SI base units.
From $p = \frac{F}{A}$ :
$Pa = {kg m}^{- 1} s^{- 2}$
True or False?
The newton is an SI base unit.
False.
The newton is a derived unit; in SI base units it is written as kg m s^-2.
Define a homogeneous physical equation.
A homogeneous physical equation is one in which the combined base units on both sides of the equation are the same.
How can you check whether a physical equation is homogeneous?
Reduce both sides of the equation to their SI base units and check they are equal. If they do not match, the equation cannot be correct.
What does it mean for a quantity to be dimensionless?
It has no units — its combined base units cancel to leave a value of 1 (for example, γ in the speed-of-sound equation).
State the symbols and powers of ten for the prefixes tera, giga, mega and kilo.
- tera (T) = 10¹²
- giga (G) = 10⁹
- mega (M) = 10⁶
- kilo (k) = 10³
The prefix milli (m) represents a factor of ...........
The prefix milli (m) represents a factor of 10^-3.
True or False?
The prefix micro (μ) represents a factor of 10^-9.
False.
The prefix micro (μ) represents 10^-6; the factor 10^-9 is nano (n).
An equation has base units of kg m s^-2 on one side and kg m² s^-2 on the other. Is it homogeneous?
No. The base units on each side are different, so the equation is not homogeneous and cannot be physically correct.

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