9th Class Physics# (2025), Measurement of Physical Quantity# and Interna...

Measurement of Physical Quantities

Physical Quantity:
A physical quantity is any quantity in physics that can be measured and expressed numerically. Examples include length, mass, time, temperature, current, etc.

Types of Physical Quantities:

1. Base Quantities:
   These are fundamental quantities that cannot be derived from other quantities. There are 7 base quantities in physics:

   • 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)

2. Derived Quantities:
   These are quantities derived from base quantities through mathematical operations. Examples include:

   • Velocity (m/s)
   • Acceleration (m/s²)
   • Force (newton, N = kg·m/s²)
   • Pressure (pascal, Pa = N/m²)

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International System of Units (SI Units)

The International System of Units (SI) is a globally accepted system for measuring physical quantities. It ensures uniformity and consistency in measurements worldwide.

Key Features of SI Units:

1. There are 7 base units corresponding to the 7 base quantities.
2. Derived units are formed using base units (e.g., speed = m/s).
3. SI prefixes are used to express multiples and submultiples of units (e.g., kilo = 10³, milli = 10⁻³).

SI Base Units:

Base 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

Common SI Prefixes:

Prefix	Symbol	Multiplier
Mega	M	$10^6$
Kilo	k	$10^3$
Deci	d	$10^{-1}$
Centi	c	$10^{-2}$
Milli	m	$10^{-3}$
Micro	μ	$10^{-6}$

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Importance of SI Units

1. Universality: Allows scientists and engineers to communicate results without confusion.
2. Consistency: Provides standardized measurements for accurate scientific research and industrial applications.
3. Convenience: Covers both large and small measurements using prefixes.

Let me know if you'd like to dive deeper into specific examples or applications!

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