Physics Intro-SI Prefixes, units, Dimensions, symbols etc

Physical Quantity

         All the quantities in terms of which laws of physics are described and which can be measured directly or indirectly are called physical quantities.

For example mass,  length,  speed, time etc. 

Types of Physics Quantity 

1) Fundamental Qualntities

       The physical quantities which do not depend upon other physical quantities are called fundamental quantities or also known as base physical quantities 

e.g.  Time, temperature, mass, length,                    electric current, luminous intensity 

        and amount of substance

2) Derived quantities 

     The physical quantities which depend on

     Fundamental quantities are called.                Derived quantities

e.g.  Acceleration, speed, force etc.

Unit

        The chosen standerd of measurement of a physical quantity, which has the same nature as that of the quantity is called the unit of that quantity. 

Choice of Unit

   The first thing is that it should have international acceptation that means Universally accepted and also accurately defined and it should not change with time.

Fundamental and Derived Units

     Fundamental units means which are independent of unit of other physical quantity and cannot be further resolve into any other units of the units of fundamental physical quantities are called

Fundamental or base units. 

e.g. metre, kilogram, second etc

All unit other than fundamental are Derived units, which are depend on fundamental units.

e.g. unit of speed (metre per sec) (which              depend upon length) 

      Unit of time, unit of momentum etc. 

Different types of system of units

C.G.S. units (Centimetre-Gram-Second) 
 In this system unit of length is centimeter,
 mass is gram and for time is second

M.K.S. units (Metre-Kilogram-Second) 
  In this system unit of length is metre, mass is kilogram and for time is second 

S.I. units (international System) 
     In 1971 CGPM held its meeting and decided a system of units which is known as S.I. (international system) of units. By international agreement, 7 physical quantities have been chosen as fundamental or base physical quantities.

S.No.	Quantity	Name of Units	Symbol
1	Length	metre	m
2	Mass	kilogram	kg
3	Time	second	s
4	Electric Current	ampere	A
5	Termodyanamic Temperature	kelvin	K
6	Amount of Substance	mole	mol
7	Luminous Intensity	candela	cd

S.No.	Supplementary   physical  quantity	Supplementary  unit	Symbol
1	Plane angle	radian	rad
2	Solid angle	steradian	sr

SI Prefixes:

Power of 10	prefix	symbol
18	exa	E
15	peta	P
12	tera	T
9	giga	G
6	maga	M
3	kilo	k
2	hecto	h
1	deka	da
-1	deci	d
-2	centi	c
-3	milli	m
-6	micro	μ
-9	nano	n
-12	pico	p
-15	femto	f
-18	atto	a

Some Important Practical Units :

(a) 1A.U.(Astronomical unit) = 1.496 × 10¹¹m

(b) 1ly (light year) = 9.46 × 10¹⁵ m

(c) 1 parsec = 3.1 × 10¹⁶ m

(d) 1 micron = 10¯⁶ m

(e) 1nanometre = 10¯⁹

(f) 1 angstrom = 10¯¹⁰

(g) 1 C.S.L(chandrasekhar limit) = 1.4 times        the mass of the sun

(h) 1 amu = 1.67×10¯²⁷ kg

(i) 1 pound = 453.6 g = 0.4536 kg

(j) 1 bar = 1atm pressure = 10⁵ N/m² = 760.         mmHg

Some Important Physical Constant 

• Velocity of light in vacuum (c) = 3 × 108 ms-1
• Velocity of sound in air at STP = 331 ms-1
• Acceleration due to gravity (g) = 9.81 ms-2
• Avogadro number (N) = 6.023 × 1023/mol
• Density of water at 4oC = 1000 kgm-3 or 1 g/cc.
• Absolute zero = -273.15oC or 0 K
• Atomic mass unit = 1.66 × 10-27 kg
• Quantum of charge (e) = 1.602 × 10-19 C
• Stefan’s constant = 5.67 × 10–8 W/m2/K4
• Boltzmann’s constant (K) = 1.381 × 10-23 JK-1
• One atmosphere = 76 cm Hg = 1.013 × 105 Pa
• Mechanical equivalent of heat (J) = 4.186 J/cal
• Planck’s constant (h) = 6.626 × 10-34 Js
• Universal gas constant (R) = 8.314 J/mol–K
• Permeability of free space () = 4π × 10-7 Hm-1
• Permittivity of free space () = 8.854 × 10-12 Fm-1
• The density of air at S.T.P. = 1.293 kg m-3
• Universal gravitational constant = 6.67 × 10-11 Nm2kg-2

Astronomical Constant 

S. No.	Quantity	Value	Unit
1	Mass of the sun	1.99×10^30	kg
2	Radius of the sun	6.95×10^8	m
3	Mass of the earth	5.98×10^24	kg
4	Mean radius of the earth	6.37×10^6	m
5	Mass of the moon	7.36×10^22	kg
6	Radius of the moon	1.74×10^6	m
7	Mean earth-sun distance	1.50×10^11	m
8	Mean earth-moon distance	3.84×10^8	m
9	Escape speed from the earth	11.2	km/s
10	Escape sore from the moon	2.38	km/s

Unit and Dimension of Physical Quantities

S.No.	Physical  Quantity	Symbol	SI Unit	Dimension
1	Displacement	s	Metre (m)	L
2	Mass	m,M	Kilogram	M
3	Time	t	Second (s)	T
4	Area	A	m2	L2
5	Volume	V	m3	L3
6	Density	ρ	kg m–3	ML–3
7	Velocity	v,u	m s–1	LT–1
8	Acceleration	a	m s–2	LT–2
9	Force	F	newton (N)	MLT–2
10	Work	W	joule (J)	ML2T–2
11	Energy	E,U,K	joule (J)	ML2T–2
12	Power	P	watt (W)	ML2T–3
13	Momentum	p	kg-m s–1	MLT–1
14	Gravitational constant	G	N-m2 kg–2	L3M–1T–2
15	Angle	Ө	radian
16	Angular velocity	ω	rad s–1	T–1
17	Angular Acceleration	∝	rad s–2	T–2
18	Angular Momentum	L	kg-m2 s–1	ML2T–1
19	Moment of inertia	I	kg-m2	ML2
20	Torque	τ	N-m	ML2T–2
21	Angular frequency	ω	rad s–1	T–1
22	Frequency	v	hertz (Hz)	T–1
23	Period	T	s	T
24	Young's modulus	Y	N m–2	ML–1T–2
25	Bulk modulus	B	N m–2	ML–1T–2
26	Shear modulus	η	N m–2	MLT–2
27	Surface tension	S	N m–1	MT–2
28	Coefficient of viscosity	η	N-s m–2	ML–1T–1
29	Pressure	P,p	N m–2, Pa	ML–1T–2
30	Wavelength	λ	m	L
31	Intensity of wave	I	W m–2	MT–3
32	Temperature	T	Kelvin (K)
33	Specific heat capacity	c	J kg–1 -K–1	L2T–2K–1
34	Stefan's constant	σ	W m–2 -K–4	MT–3K–4
35	Heat	Q	J	ML2T–2
36	Thermal conductivity	K	W m–1 -K–1	MLT–3K–1
37	Current	I	Ampere (A)	I
38	Charge	q,Q	coulomb (C)	IT
39	Current density	j	A m–2	IL–2
40	Electrical conductivity	σ	1/Ω -m	I2T3M–1L–3
41	Dielectric constant	k
42	Electric dipole moment	p	C-m	LIT
43	Electric field	E	Vm–1	MLI–1T–3
44	Potential	V	volt (V)	ML2I–1T–3
45	Electric flux	Φ	V-m	ML3I–1T–3
46	Capacitance	C	farad (F)	I2T4M–1L–2
47	Electromotive force	E	volt (V)	ML2I–1T–3
48	Resistance	R	ohm (Ω)	ML2I–2T–3
49	Permittivity of space	ε0	C2N–1 -m–2	I2T4M–1L–3
50	Permeability of space	μ0	N A–2	MLI–2T–2
51	Magnetic field	B	tesla (T)	MI–1T–2
52	Magnetic flux	Φ0	weber (Wb)	ML2I–1T–2
53	Magnetic	μ	N-mT–1	IL2
54	Inductance	L	henry (H)	ML2I–2T–2