Units And Measurements, Fundamentals, Types Of Physical Quantities

Units And Measurements: In order to quantify physical quantities such as mass, length, and time, we need a standard measurement. The unit of that physical quantity is this measurement standard. For instance, the metre is the unit of length, and one metre is a conventional length with a defined meaning. Finding the number of times this standard length meter is contained in an object's length is necessary to calculate its length. Comparing a physical quantity with a standard quantity is the process of measurement. Students can read all the information about Units And Measurements in the below article.

NEET Syllabus 2024

Units And Measurements

NEET Physics Chapter wise Weightage

Units And Measurements Fundamentals

1. Mass
2. Current
3. Time
4. Temperature
5. Length
6. Substance Amount
7. Luminous Intensity

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Physical Quantity

Physical quantity = Numerical value (N) × Unit (U)

Units

• A Unit of measurement is a reference standard used to express a physical quantity in multiples of that standard.
• A Measurement is expressed as a numerical value plus the appropriate unit.
• Example: metre, newton, second, kilogram, joule, watt etc.

Types Of Physical Quantities

Fundamental Physical Quantities

Plane Angle (Radian) (Rad)

Solid Angle (steradian) (sr)

• An angle in three dimensions is called a solid angle.
• It is the angle in the center of a spherical surface of unit radius that any portion of the surface subtends.
• It is represented as Ω.
• An angle that is solid has no dimensions.
• The steradian is the SI unit for solid angle.
• If A is the area of a portion of the spherical surface and r is the sphere's radius, the solid angle may be found using the following formula:

Ω = A/d2

where, W = 2Ar

• A = Area
• W = Solid angle
• r = radius

Derived Physical Quantity

Astronomical Unit

1 AU= $1.496\times {10}^{11}m$

Light Year

• The unit of distance is one light-year.
• It is the distance that a light photon covers in a Julian year while it is in the vacuum.
• Value of one light-year is constant and is represented by ly.
• Astrophysics frequently uses the phrase "light-year" to refer to the separation between two celestial objects.
• The speed of light is approximately 300,000 kilometers per second.
• It has a 10 trillion km trip range.

Parallactic Angle

Units of Lengths

1. parsec 1 parsec = 3.084 × 1016 m
2. Light year (ly) 1ly = 9.46 × 1015 m
3. 1 A.U (distance between sun and earth) 1 A.U = 1.496 × 1011 m
4. fermi 1 fm = 10–15 m
5. angstrom (Å) 1Å = 10–10 m
6. nanometre (nm) 1 nm = 10–9 m
7. Units of Mass
8. Atomic mass unit (amu) 1 amu = 1.66 × 1027 kg
9. Quintal 1 Quintal = 100 kg

Dimensions And Examples In Units And Measurements

Dimensionless Quantity

Dimensional Analysis

Applications of Dimensional Analysis

1. To determine whether a dimensional equation is consistent
2. To determine how physical quantities relate to one another in physical phenomena
3. To convert units between different systems

Principle of Homogeneity

Limitations of Dimensional Analysis

1. It provides no details regarding the dimensional constant.
2. It is not possible to derive the formula containing the logarithmic function, exponential function, and trigonometric function, among others.
3. It provides no information regarding the vector or scalar nature of a physical quantity.

Errors, Significant Figures

Significant Figures and Rounding off

Rules of Rounding off The Uncertain Digits Upto 3 Significant Figures

Accuracy

Precision

Errors In A Measurement

Systematic Error

• y Instrumental error (zero error)
• y Wrong experimental technique
• y Personal error

Random Error

Combination of Errors

Measuring Instruments

Least Count

• A meter scale is used for lengths from 10–3 m to 102 m
• y A vernier calipers is used for lengths to an accuracy of 10–4m.
• y A screw gauge and spherometer can be used to measure lengths as less as to 10–5m.

Metre Scale

Vernier Caliper

Screw Gauge

Uses of Screw Gauge

Least Count of Screw Gauge

Negative Zero Error