INTRODUCTION-

Unit – A unit is a standard measure for quantifying physical quantities .

Types of unit –

1). Fundamental or Basic units – Unit of fundamental or base quantity is called fundamental or base unit .(fundamental unit are also called base unit)

2). Derived Units – Unit obtained form derived quantity is called derived unit .

Both fundamental and Base unit are called System Of Units .

3). SUPPLEMENTARY UNIT–

Supplementary unit have 2 types

1- Radian or Plane angle or 2D Angle -1 radian is angle subtended from the center of circle which intercepts an arc equal in length to the radius of a circle.

radian = arc/radii

2- Solid angle or Steradian- 1 steradian is the solid angle subtended at the center sphere by its surface whose area is equal to square of radius

Steradian= area/(radius)^2

THE INTERNATIONAL SYSTEM OF UNITS –

Earlier scientists of different countries used different units for measurement. There are 3 system for measurement ,CGS(centimeter gram second), MKS(meter kilogram second) and FPS or british system (foot pound second).

The system of unit which is accepted Internationally for measurement is called SI units(System International).

In SI, have 7 base (or fundamental unit) units-

QUANTITY  NAMEUNIT  NAMESYMBOL  NAME
LengthMeterm
MassKilogramkg
TimeSecondS or sec.
Electric CurrentAmpereA
Thermodynamic TemperaturekelvinK
Amount of SubstanceMolemol
Luminous IntensityCandelacd

SIGNIFICANT FIGURES –

Significant Figures – It is a meaningful digits in measurement that showing its precision and accuracy .

There are 5 rules to determine significant figures –

  1. All the non-zero digit are significant (ex.-122 have 3 significant fig.).
  2. All zeros between non zero digit are significant (ex.-10034 have 5 significant fig.)
  3. If number is less than one, the zero(s) on right of decimal point are significant(ex- 0.0012 is 2 SF)
  4. The repeating zeros without decimal point is not significant(ex.- 1400 have 2 sig. fig.)
  5. The repeating zeros after decimal point and digit is significant(ex.-3.400 have 4 sig. fig.)
  6. Every constant have infinite significant figures(ex. pie have infinite sig. fig.)
  7. in scientific notation only digits consider not 10 and its power(ex.-1.2*10^5 have 2 sig. fig.)

SCIENTIFIC NOTATION –

When a number written in a form of a*10^b is called scientific notation (ex.- 14900000 = 1.49*10^7 is its scientific notation).

RULES OF ARITHMETIC OPERATION WITH SIGNIFICIANT FIGURES –

For Multiply and Divide –

First do simple multiply or divide what question ask , then identify which have least significant digits.

In answer number of significant digits is equal to number of least significant digits (ex-5.1*0.1=0.51 answer is 0.5) .

For Addition and Subtraction-

First do simple multiply or divide what question ask , then identify that which have least number significant figures after decimal .

In answer number of significant figures are equal to least sig. fig. after decimal (ex-1.3+0.33+1.11=2.74 ,answer is 2.7).

ROUNDING OFF THE UNCERTAIN DIGITS-

There are 3 main rule of rounding off on uncertain digits

If question says that round of up to 2 significant figures ,then  check that 3rd significant figure –

  1.  If 3rd digit is less than 5 ,then remove 3rd digit and write all number as it is.
  2. If 3rd digit is greater than 5 ,then increase 2nd digit by 1 and write .
  3. If 3rd digit is equal to 5 ,then check number is even ,if even write as it is otherwise increase by 1 (ex-rounding off of 1.23 is 1.2).

DIMENSION OF PHYSICSAL QUANTITY-

  • All physical quantity represent in term of fundamental (or base) quantity .
  • There are seven base quantity and all have own dimensions .
  • Dimension of all quantity represented by square bracket (ex-mass –[M] and time-[T] etc.)*our syllabus has 3 dimension vis.[M],[L],[T]*
  • The DIMENSION of quantity is power where the base quantities represent that quantity .
  • Ex.- force=mass*acceleration , F=[M]*[L]/[T]2=F=[MLT-2]
  • Dimension of other than base quantity is zero and also every number have no dimension .
  • DIMENSIONAL FORMULA-The expression of the physical quantity in terms of its basic unit with proper dimension(F-[MLT-2]).

DIMENSION ANALYSIS AND ITS APPLICATION –

  1. To check the correctness of any physical equation.
  2. To convert unit system of any physical quantity.
  3. To derive new physical formula from given data.

The velocity cannot be added to force ,or an electric current cannot be subtracted to thermodynamic temperature , this is called the Principal Of Homogeneity Of Dimensions.

There are some important Dimensions of some physical quantity. At the end of per chapters have some dimensions .

S. No.Physical  Qnt.FormulaDimensionalDimensional FormulaUnit (SI)
1Area of square(Side)2[L2][M0L2T0](Meter)2
2DensityMass/Vol.[M]/[L3][M1L-3T0]Kg/m3
3AccelerationVelocity/Time[L1T-2][M0L1T-2]Meter/sec2
4Momentum(P)P=mass*velocity[M1L1]/[T1][M1L1T-1]Kg.m/sec
5ForceMass*Acc.[M1 L1 T-2][M1 L1 T-2]Kg.m/sec2 or N
6AngleArc/Radius[L]/[L]Dimension lessDegree&radian
7PowerWork/Time[M1 L2 T-2]/[T1][M1 L2 T-3]Kg.m2/sec3&watt
1012  – Tera(T)
109 – Giga(G)
106 – Mega(M)
103– Kilo(K)
10-3– Milli(m)
10-6– Micro(u)
10-9Nano(n)
10-12– Pico(p)

These all are the notes of chapter 1 in physics. And after some time you get important questions and NCERT solutions HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊