O LEVEL PHYSICS (5054) PHYSICAL QUANTITES, UNITS AND MEASURING INSTRUMENTS

Physical Quantities, Units and
Measurements
Sub Topics:
1. Physical Quantity
2. SI units
3. Base Units
4. Derived Units
5. Prefix
6. Scalar and Vector
7. Measuring Instruments



 Physical Quantity:
A quantity which can be measured and expressed in
numbers. For example
1. Mass
2. Time
3. Temperature
4. Volume
5. Distance
6. Current



SI Unit:
A SI unit is needed to express a physical quantity.
There are two kinds of SI units
1. Base SI unit

, 2. Derived SI unit


Base SI unit:
One of a set of fundamental units in a system of
measurement that is based on a natural phenomenon or
established standard and from which other units may be
derived.
S# Base Quantity Base SI unit Symbol
1. Length (l) meter m

2. Mass (m) kilogram Kg
3. Time (t) second s
4. Temperature kelvin K
(T)
5. Electric Ampere A
current (I)


Derived SI units:
A derived unit is a unit that results from a mathematical
combination of SI base units. For example:
 SI unit of Force is newton (N)
 SI unit of Pressure is pascal (Pa)
 SI unit of Work is joule (J)
 SI unit of Power is watt (W)
 SI unit of Charge is coulomb (C)
 SI unit of potential difference is Volt (V)
And so, on