## Physical Quantities

 1.1 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 $$=$$ $$-$$

 Prefix 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 $$km$$. $$200\div10^3=0.2\,km$$

 Prefix $$\rightarrow$$ No prefix ( $$\times$$ ) Example : Convert $$0.2\,km$$ to $$m$$. $$0.2\times10^3=200\,m$$

 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