Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Measurement: Physical Quantities, Units and Measurement
Candidates should be able to:
n
a) show understanding that all physical quantities consist of a numerical magnitude and a unit
tio
b) recall the following base quantities and their units: mass (kg), length (m), time (s), current (A),
temperature (K), amount of substance (mol)
ca
c) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the
SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G)
typical atom to the Earth
Ed
u
d) show an understanding of the orders of magnitude of the sizes of common objects ranging from a
e) state what is meant by scalar and vector quantities and give common examples of each
f) add two vectors to determine a resultant by a graphical method (#)
l
g) describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules,
ny
a
micrometers and calipers, using a vernier scale as necessary
h) describe how to measure a short interval of time including the period of a simple pendulum with
Da
appropriate accuracy using stopwatches or appropriate instruments
* not in combined Science syllabus
# not in N level Science syllabus
O Level Physics – Physical Quantities, Units and Measurement
1
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
A physical quantity is a quantity that can be
measured.
Eg, length, area, volume, velocity, acceleration
It consists of a numerical magnitude and a
measurement unit.
What is a vector quantity? Give 3 examples.
It is a physical quantity with both numerical
magnitude and direction.
Examples: force, velocity, acceleration, weight,
displacement (any 3)
10n
Value
tera-
1012
One trillion
T
giga-
109
One billion
G
mega-
106
One million
M
kilo-
103
One thousand
k
deci-
10-1
n
What are the common prefixes used to describe larger
or smaller quantities?
One tenth
d
10-2
One hundredth
c
One thousandth
m
One millionth
μ
Prefix
centimilli-
Symbol
tio
What is a physical quantity?
10
-3
What is a scalar quantity? Give 3 examples.
micro-
It is a physical quantity with only numerical
magnitude.
Examples: mass, energy, time, volume, density,
power, temperature, speed (any 3)
nano-
10-9
One billionth
n
pico-
10-12
One trillionth
p
Ed
u
ca
10-6
What are the 7 base quantities?
What is the size of a typical atom?
The diameter of a typical atom is around 10-10
metres.
l
Arrange these objects in ascending orders of
magnitude in terms of their sizes: a mountain; an
atom; planet Earth; a bus; a paper clip; an electron;
the Sun
ny
a
An electron; an atom; a paper clip; a bus; a
mountain; planet Earth; the Sun.
Physical Quantity
S.I. Unit
Symbol
Length
metre
m
Mass
kilogram
kg
Temperature
Kelvin
K
Time
second
s
Current
ampere
A
Amount of
mole
mol
candela
cd
substance
Luminous Intensity
How do you decide which instrument to use when taking measurements of length?
Da
The instrument to use will depend on the length to be measured and the degree of accuracy of
measurement required.
Length to be
Instrument to use
measured
Accuracy of
measurement
Below 2cm
Micrometer screw
To the nearest 0.001cm
gauge
Between 0 and 10 cm
Vernier calipers
To the nearest 0.01cm
10cm to 100cm
Metre rule
To the nearest 0.1cm
5cm and above
Measuring tape
To the nearest 0.1cm
O Level Physics – Physical Quantities, Units and Measurement
2
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Da
ny
a
l
Ed
u
ca
tio
n
Describe how to measure the period of a simple pendulum.
O Level Physics – Physical Quantities, Units and Measurement
3
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Da
ny
a
l
Ed
u
ca
tio
n
A vernier calipers
O Level Physics – Physical Quantities, Units and Measurement
4
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Da
ny
a
l
Ed
u
ca
tio
n
A micrometer screw gauge
O Level Physics – Physical Quantities, Units and Measurement
5
c) main scale: 8.1cm
vernier scale: 0.08cm
reading: 8.18cm
tio
b) main scale: 3.6cm
vernier scale: 0.06cm
reading: 3.66cm
Ed
u
ca
a) main scale: 6.1cm
vernier scale: 0.05cm
reading: 6.15cm
n
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Da
ny
a
l
Zero error: +0.04cm
Unadjusted reading: 5.29cm
Adjusted reading = Unadjusted reading – zero error
= 5.29cm – (+0.04cm)
= 5.25cm
a) zero error: - 0.04cm
b) Adjusted reading = 1.78cm – (-0.04cm) = 1.82cm
O Level Physics – Physical Quantities, Units and Measurement
6
ca
b) Adjusted reading = 6.73 – (-0.02) = 6.75mm
b) Zero error = 5.09 – 5.06 = +0.03mm
Da
a) 5.09mm
ny
a
l
Ed
u
a) Negative zero error: -0.02mm
tio
n
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
O Level Physics – Physical Quantities, Units and Measurement
7
Danyal Education (Contact: 9855 9224)
“A commitment to teach and nurture”
Da
ny
a
l
Ed
u
ca
tio
n
Vector Diagram
O Level Physics – Physical Quantities, Units and Measurement
8