Physical Quantities


 Physical Quantities

  What is physics?  
  • A knowledge to find a rational explanation (why and how) of the nature of matter, energy and natural phenomena.
  • Involves the quantity being measured, formula and matter
  • Many theories are proved through calculations
  • Use of standard units
  Field of Physics  
  • Heat
  • Light
  • Electrical and electronics
  • Astronomy
  • Nuclear
  • Biophysics
  • Wave
  • Force and motion
  • Plasma physics
  Physical quantities  
  • contains magnitude and unit
  • can be measured
Base quantities : Derived quantities :
Physical quantities that cannot be defined in terms of other physical quantities. A physical quantity that is derived by a combination of base quantities. Can be done by multiplication, division or both.
Example : Example :
  • length, \(\text{l}\) (\(m\))
  • mass, \(\text{m}\) (\(kg\))
  • time, \(\text{t}\) (\(s\))
  • temperature, \(\text{T}\) (\(K\))
  • current, \(\text{I}\) (\(A\))

(Other than base = derived)

  • area, \(\text{l}\times\text{l}\) (\(m^2\))
  • volume, \(\text{v}=\text{l}\times\text{l}\times\text{l}\) (\(m^3\))
  • density, \(\dfrac{\text{m}}{\text{v}}\) (\(kgm^{−3}\))
  • speed, \(\dfrac{\text{l}}{\text{t}}\) (\(ms^{−1}\))
  • acceleration, \(\dfrac{\text{speed}}{\text{t}}\) (\(ms^{−2}\))
  Standard form  

Standard form is a way of writing down very large or very small numbers easily and without using lots of zeros. We sometimes call it scientific notation. 

\(A\times10^n\;,\;1\leq A < 10\)

  Question examples  

 Example 1 :

Convert \(135\) to standard numbers.

\(\;\curvearrowleft\curvearrowleft\\1\,3\,5\;. \rightarrow 1.35 \times 10^2\)

two decimal move to the left \(=\) \(+\)


 Example 2 :

Convert \(0.00008\) to standard numbers.

\(\;\;\curvearrowright\curvearrowright\curvearrowright\curvearrowright\curvearrowright\\0.0\;\;0\;\;0\;\,0\,\;8 \rightarrow 8 \times 10^{-5}\)

five decimal move to the right \(=\) \(-\)

  Prefixes are the preceding factor used to represent very small and very large physical quantities in SI units.  
Prefix Symbol Standard form
tera \(T\) \(10^{12}\)
giga \(G\) \(10^{9}\)
mega \(M\) \(10^{6}\)
kilo \(k\) \(10^{3}\)
hecto \(h\) \(10^{2}\)
deka \(da\) \(10^{1}\)
deci \(d\) \(10^{-1}\)
centi \(c\) \(10^{-2}\)
milli \(m\) \(10^{-3}\)
micro \(µ\) \(10^{-6}\)
nano \(n\) \(10^{-9}\)
pico \(p\) \(10^{-12}\)

No prefix \(\rightarrow\) Prefix ( \(\div\) )


Example : Convert \(200\,m\) to \(km\).



Prefix \(\rightarrow\) No prefix ( \(\times\) )


Example : Convert \(0.2\,km\) to \(m\).


Scalar quantity Vector quantity
Physical quantity that has only magnitude Physical quantity that has both magnitude and direction
Example:  Distance, speed, time, mass, energy Example: Displacement, velocity, weight, force