Chapter 1 Physical Quantities & Measurement

CHAPTER 1

Physical Quantities and Measurement

Learning outcomes

The students will be able to:

·         1. Describe base quantities, derived quantities and the International System (SI) of units.

·        2. Define scalar and vector quantities, unit conversion.

·         3.Interpret data of measurement

·         4.Describe inaccuracy and errors in measurement

·         5.Measurement equipments:-

-  Ruler

- Vernier Callipers

-  Micrometer Screw Gauge

“ Little knowledge of science makes man an atheist, but in-depth study of

science makes him a believer in God ” 

*Francis Bacon*

INTRODUCTION

Physics is a branch of science which studies physical and natural phenomena around us. The principles and concepts of physics are then applied in our daily life. The word physics actually comes from the Greek word “physikos” which means nature.

Base    Base Quantities

A base quantity is a physical quantity which cannot be defined in terms of other physical quantities.

Base Quantity	Symbol	SI unit	Symbol of unit
Length	l	Meter	m
Mass	m	Kilogram	kg
Time	t	Second	s
Temperature	T	Kelvin	K
Current	I	ampere	A

Derived Quantities

A derived quantity is a physical quantity produced from the combination of base quantities through multiplication, division or both.

PREFIXES

Prefixes are used to represent physical quantities which are very big or very small in SI units.

SCALAR QUANTITIES

 Scalar quantities are physical quantities with magnitude only.

VECTOR QUANTITIES

Vector quantities are physical quantities with direction and magnitude.

UNIT CONVERSION

Unit conversion is a multi-step process that involves multiplication or division by a numerical factor, selection of the correct number of significant digits, and rounding.

BASIC MEASURING INSTRUMENTS

TYPES OF INSTRUMENT	RULER	VERNIER CALLIPERS	MICROMETER SCREW GAUGE
Accuracy	0.1cm	0.01cm	0.001cm
Sensitivity	Less sensitive	Slightly sensitive	More sensitive

EXPERIMENTAL ERRORS 

a)      Systematic Error 

A systematic error is an error in reading the scale when a physical quantity is being measured. It is caused by the instrument 

b)       Random Error

A random error is an error which occurs when the observer is reading the scale on the measuring instrument.

Examples of random errors are :

 (a) Parallax error

                            (b) Error in the reading of scale.

 (c) Error due to a change in temperature as the experiment is being carried out.

                            (d) Error due to miscount, for example when counting the number or oscillations of 

                             simple pendulum.

MEASURING INSTRUMENTS

Ruler

Vernier Caliper

Micrometer Screw Gauge