Class 11 Physics Physical Quantity Notes || class 11 physics chapter 1 physical quantities notes || class 11 physics physical quantity notes 2025

 

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1. Chapter 1: Physical Quantities and Measurement

   1. Physical Quantities

   A physical quantity is a property of a material or system that can be quantified by measurement.
   Examples: Length, Mass, Time, Force, etc. 

   2. Types of Physical Quantities

   Type	Definition	Examples
   Fundamental	Independent, base quantities	Length (m), Mass (kg), Time (s)
   Derived	Expressed in terms of fundamental units	Velocity (m/s), Force (N)
   Scalar	Only magnitude	Mass, Temperature, Energy
   Vector	Magnitude + Direction	Force, Velocity, Acceleration

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   3. Fundamental (Base) Quantities & Their SI Units

   The SI system has 7 fundamental quantities:

   Quantity	SI Unit	Symbol
   Length	meter	m
   Mass	kilogram	kg
   Time	second	s
   Electric Current	ampere	A
   Temperature	kelvin	K
   Amount of Substance	mole	mol
   Luminous Intensity	candela	cd

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   4. Derived Quantities & Their Units

   Derived from fundamental quantities.

   Quantity	Formula	SI Unit	Symbol
   Force	F = ma	newton (N)	kg·m/s²
   Energy	E = F × d	joule (J)	kg·m²/s²
   Power	P = E/t	watt (W)	J/s
   Pressure	P = F/A	pascal (Pa)	N/m²
   Velocity	v = d/t	m/s	m·s⁻¹

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   5. Scientific Notation & Prefixes

   Used to express very large/small numbers.

   Prefix	Symbol	Multiplier
   pico	p	10⁻¹²
   nano	n	10⁻⁹
   micro	μ	10⁻⁶
   milli	m	10⁻³
   kilo	k	10³
   mega	M	10⁶
   giga	G	10⁹

   Example:

   • 1 μm = 10⁻⁶ m

   • 1 GHz = 10⁹ Hz

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   6. Dimensional Analysis

   Used to check equations and derive relationships.
   Dimensions of fundamental quantities:

   • [Length] = L

   • [Mass] = M

   • [Time] = T

   Example:
   Force = mass × acceleration
   → [F] = [M][LT⁻²] = MLT⁻²

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   7. Significant Figures

   Rules for counting significant digits:

   1. Non-zero digits are always significant.

   2. Zeros between non-zero digits are significant.

   3. Leading zeros are not significant.

   4. Trailing zeros after a decimal are significant.

   Example:

   • 0.0045 → 2 significant figures

   • 3.400 → 4 significant figures

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   8. Errors in Measurement

   Error Type	Definition
   Systematic	Consistent, due to instrument/fault
   Random	Unpredictable, due to fluctuations
   Absolute	Difference between measured & true
   Relative	(Absolute error / True value) × 100

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   9. Accuracy vs Precision

   Term	Meaning
   Accuracy	Closeness to the true value
   Precision	Closeness of repeated measurements

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   Key Formulas

   1. Percentage Error = $\frac{\mathrm{\mid }\text{True Value}-\text{Measured Value}\mathrm{\mid }}{\text{True Value}}\times 100$

   2. Relative Error = $\frac{\text{Absolute Error}}{\text{True Value}}$