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Measurements - Chapter 1 (Physics)

Key Points

Physics (definition)

Physics deals with study of matter and energy and relationship between them.

Some Areas of Physics

  1. Classical Mechanics
  2. Quantum Mechanics
  3. Heat and Thermodynamics
  4. Electromagnetism
  5. Optics
  6. Sound
  7. Special Relativity
  8. Atomic Physics
  9. Molecular Physics
  10. Nuclear Physics
  11. Solid State Physics
  12. Particle Physics
  13. Plasma Physics
  14. Space Physics

Some Interdisciplinary Areas of Physics

  1. Astrophysics
  2. Biophysics
  3. Engineering Physics
  4. Geophysics
  5. Health Physics
  6. Medical Physics
  7. Physical Chemistry

Physical Quantities

The quantities in terms of which the laws of Physics are expressed.
Physical quantities are divided in 2 categories:

  1. Base Quantities
  2. Derived Quantities

Base Quantities

These quantities are not defined in terms of other physical quantities.
e.g. length, mass, time

Derived Quantities

These quantities are those whose definitions are based on other physical quantities.
e.g. velocity, acceleration, force

System International (SI)

It is an international system of units. It consists of 3 kinds of units:

  1. Base units
  2. Supplementary units
  3. Derived units
Base Units (7)
Physical Quantity SI Unit Symbol
Length metre m
Mass kilogram kg
Time second s
Electric Current ampre A
Temperature kelvin K
Intensity of Light candela cd
Amount of substance mole mol
Supplementary Units (2)
Physical Quantity SI Unit Symbol
Plane angle radian rad
Solid angle steradian sr

Derived Units

SI units for all other physical quantities are derived the base and supplementary units. Some examples are given in the the table:

Derived Units
Physical Quantity SI Unit Symbol In terms of base units
Force newton N kg m s-2
Work joule J N m = kg m2 s-2
Power watt W J s-1 = kg m2 s-3
Pressure pascal Pa N m-2 = kg m-1 s-2
Electric Charge coulomb C A s

Scientific Notation

A standard form which employs powers of 10. There should be only 1 non-zero digit left of decimal.
e.g. 134.7 = 1.347 x 102, 0.0023 = 2.3 x 10-3

Some Prefixes of powers of 10
Factor Prefix Symbol
10-18 atto a
10-15 femto f
10-12 pico p
10-9 nano n
10-6 micro u
10-3 milli m
10-2 centi c
10-1 deci d
101 deca da
103 kilo k
106 mega M
109 giga G
1012 tera T
1015 peta P
1018 exa E

Some Conventions for Indicating Units

  1. Full name of a unit does not begin with a capital letter
    e.g. newton
  2. The symbol of unit named after a scientist has initial capital letter
    e.g. N for newton
  3. A combination of base units is written each with one space apart.
    e.g. newton metre is written as N m
  4. Compound prefixes are not allowed.
    e.g. 1uuF may be written as 1pF
  5. 1 km2 = 1 (km)2 = 1 x 106 m2

Causes of Errors

  1. negligence or inexperience of a person
  2. the faulty apparatus
  3. inappropriate method/technique

Types of Errors

  1. Random Error

    Repeated measurements of the quantity, give different values under the same conditions.
    Repeating the measurement several times and taking an average can reduce the effect of random errors.

  2. Systematic Error

    An effect that influences all measurements of a particular quantity equally due to zero error of instruments, poor calibration of instruments or incorrect markings etc.
    This error can be reduced by calibrating the instrument or by applying a correction factor.

Significant figures

In any measurement, the accurately known digits and the first doubtful digit are called significant figures.

Precision and Accuracy

The precision of a measurement is determined by the instrument or device being used and the accuracy of a measurement depends on the fractional or percentage uncertainty in that measurement.

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