Physics class 11th chapter 1 detailed notes, Study notes of Physics

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UNITS AND

MEASUREMENTS

Class-11th

Physical Quantity refers to any property of a material or system that can be measured and expressed numerically along with a unit. For example, mass, length, time, temperature, and velocity are physical quantities.

Physical Quantities Physical Quantities

Components of a Physical Quantity Components of a Physical Quantity

Numerical Value: Indicates the magnitude of the quantity. Unit: Specifies the measurement standard (e.g., meter, kilogram). Physical Quantity = Numerical Value + Unit

Fundamental units are standard units used to measure fundamental physical quantities such as length, mass, time, temperature, electric current, amount of substance, and luminous intensity. There are seven fundamental units, and they are independent; they cannot be derived from any other units. Examples: Length (meter), Mass (kilogram), Time (second), Temperature (kelvin), Electric current (ampere), Amount of substance (mole), Luminous intensity (candela).

Fundamental Units Fundamental Units

Q. Write the SI unit of the following derived quantities:

1.Force

2.Pressure

3.Work

4.Power

5.Energy

For measurements to be universally understood and comparable,

we need a complete set of units for all physical quantities. This

complete set is called a system of units.

Major systems of units are:

FPS System: Foot, Pound, Second.

CGS System: Centimeter, Gram, Second.

MKS System: Meter, Kilogram, Second.

SI System (International System of Units).

Systems of Units Systems of Units

MKS System (Meter-Kilogram-Second): Fundamental Units: Length: Meter (m), Mass: Kilogram (kg), Time: Second (s) Widely used in mechanics and larger-scale measurements.

This is the globally accepted system for scientific and technical measurements. It consists of: Seven base units Derived units.

SI Units SI Units

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) 7 Fundamental SI Units 7 Fundamental SI Units

Plane Angle: Represents the angle between two intersecting lines or surfaces. SI Unit: Radian (rad). Solid Angle: Represents the three-dimensional angle subtended by a surface at a point. SI Unit: Steradian (sr). Types of Supplementary Quantities Types of Supplementary Quantities

Conversions of Units: ConceptConversions of Units: Concept Represented as: P.q. = n × u Example: Conversion of 3 meters to centimeters: n 1 ⋅ u 1 = n 2 ⋅ u 2 3 m = 300 cm

Physical Quantity = Numerical Value + Unit

Where: n = Numerical value u = Unit Conclusion: Numerical value (n) is inversely proportional to the unit (u): n ∝ 1/u For a constant physical quantity: n⋅u = constant n u

Prefixes for SI Units:Prefixes for SI Units:

Q. Convert 72 km/h into CGS unit of velocity.

Q. The value of acceleration due to gravity is 980 cm/s. What will be its value if the unit of length is kilometer and the unit of time is minute? 2

Physical Quantity Dimension Symbol Length [L] Mass [M] Time [T] Electric Current [A] (or [I]) Thermodynamic Temperature [K] (or [Θ]) Amount of Substance [mol] (or [N]) Luminous Intensity [cd] (or [J])

Dimensions Dimensions

The dimensions of a physical quantity are the powers to which the fundamental quantities (mass, length, time, etc.) must be raised to represent that quantity. Fundamental Quantities and Fundamental Quantities and Their Dimensions Their Dimensions