Introduction to Units and Measurement Notes for NEET Physics

  

Introduction to Units and Measurement (NEET Level – Easy Notes) 

Introduction to Units and Measurement – Complete NEET Physics Mind Map and Quick Revision Notes.

- Dr.Sanjaykumar Pawar 

1. Measurement

• Measurement means finding the value of a physical quantity by comparing it with a standard quantity.
• Example: To measure the length of a table, we compare it with a standard unit like metre (m).

2. Physical Quantity

• A physical quantity is any quantity that can be measured.
• Examples: Length, mass, time, temperature, force, speed, etc.

3. Unit

• A unit is a fixed standard used to measure a physical quantity.
• It is internationally accepted and remains the same everywhere.
• Examples:
  • Length → metre (m)
  • Mass → kilogram (kg)
  • Time → second (s)

4. Why Do We Need Units?

• Units provide a common standard for measurement.
• Without units, measurements would be confusing and inconsistent.
• Example: Saying "the rod is 5" is incomplete. We must say "the rod is 5 metres long."

5. Result of Measurement

• Every measurement has two parts:
  1. Numerical value (number)
  2. Unit
• Example:
  • Length = 10 m
  • Here, 10 is the numerical value and m is the unit.

6. Number of Physical Quantities

• There are a very large number of physical quantities in physics.
• However, only a limited number of basic units are needed to express all of them.
• This is because many physical quantities are related to one another.

7. Fundamental (Base) Quantities

• Fundamental quantities are basic physical quantities that do not depend on other quantities.
• Examples:
  • Length
  • Mass
  • Time
  • Electric current
  • Temperature
  • Amount of substance
  • Luminous intensity

8. Fundamental (Base) Units

• The units of fundamental quantities are called fundamental or base units.
• Examples:
  • Length → metre (m)
  • Mass → kilogram (kg)
  • Time → second (s)

9. Derived Quantities

• Quantities that can be expressed using fundamental quantities are called derived quantities.
• Examples:
  • Speed = Distance / Time
  • Force = Mass × Acceleration
  • Density = Mass / Volume

10. Derived Units

• Units obtained by combining base units are called derived units.
• Examples:
  • Speed → m/s
  • Force → kg·m/s² (newton, N)
  • Density → kg/m³

11. System of Units

• A complete collection of base units and derived units is called a system of units.
• It provides a standard method of measurement.

12. SI System (Most Important for NEET)

• SI stands for International System of Units.
• It is the globally accepted system of units.
• It contains 7 base units.

Fundamental Quantity	SI Unit	Symbol
Length	metre	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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NEET Quick Revision Points

✅ Measurement = Comparison with a standard unit.

✅ Physical Quantity = Quantity that can be measured.

✅ Measurement result = Numerical value + Unit.

✅ Fundamental quantities are independent quantities.

✅ Fundamental units are units of fundamental quantities.

✅ Derived quantities depend on fundamental quantities.

✅ Derived units are combinations of base units.

✅ System of units = Collection of base units + derived units.

✅ SI system is the internationally accepted system of units.

One-Line Formula

Physical Quantity = Numerical Value × Unit

Example: Length = 5 m = 5 × metre. 

Below are CBSE Class 11 Physics (Units and Measurements – Introduction) exam-oriented questions with answers.

1. Multiple Choice Questions (MCQs)

Q1. Measurement of a physical quantity involves comparison with:

(a) Instrument
(b) Unit
(c) Formula
(d) Constant

Answer: (b) Unit

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Q2. The internationally accepted standard for measurement is called:

(a) Scale
(b) Instrument
(c) Unit
(d) Quantity

Answer: (c) Unit

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Q3. Which of the following is a fundamental quantity?

(a) Force
(b) Speed
(c) Length
(d) Density

Answer: (c) Length

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Q4. Which of the following is a derived quantity?

(a) Mass
(b) Time
(c) Temperature
(d) Force

Answer: (d) Force

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Q5. SI unit of length is:

(a) cm
(b) km
(c) metre
(d) inch

Answer: (c) metre

---

Q6. The SI unit of mass is:

(a) gram
(b) kilogram
(c) tonne
(d) pound

Answer: (b) kilogram

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Q7. Which is NOT a fundamental quantity?

(a) Length
(b) Mass
(c) Time
(d) Speed

Answer: (d) Speed

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Q8. A complete set of units is called:

(a) Physical quantity
(b) Standard
(c) System of units
(d) Measurement

Answer: (c) System of units

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2. Very Short Answer Questions (1 Mark)

Q1. What is measurement?

Answer: Measurement is the comparison of a physical quantity with a standard unit.

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Q2. Define unit.

Answer: A unit is a fixed standard used for measuring a physical quantity.

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Q3. What are fundamental quantities?

Answer: Quantities that are independent and cannot be expressed in terms of other quantities.

---

Q4. Give one example of a derived quantity.

Answer: Force.

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Q5. Write the SI unit of time.

Answer: Second (s).

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3. Short Answer Questions (2–3 Marks)

Q1. What is a physical quantity? Give two examples.

Answer: A physical quantity is a quantity that can be measured and expressed by a number and a unit.

Examples:

1. Length
2. Mass

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Q2. Differentiate between fundamental and derived quantities.

Fundamental Quantity	Derived Quantity
Independent quantity	Depends on fundamental quantities
Cannot be expressed in terms of other quantities	Can be expressed using fundamental quantities
Example: Length	Example: Speed

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Q3. What are derived units? Give two examples.

Answer: Units obtained by combining fundamental units are called derived units.

Examples:

1. Speed = m/s
2. Force = kg m s⁻²

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Q4. Why are units necessary?

Answer: Units are necessary because they:

• Provide a standard for measurement.
• Make communication of measurements clear.
• Allow comparison of physical quantities.

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4. Long Answer Questions (5 Marks)

Q1. Explain fundamental quantities and derived quantities with examples.

Answer:

Fundamental Quantities

• These are basic physical quantities.
• They do not depend on other quantities.
• Examples: Length, Mass, Time.

Derived Quantities

• Quantities derived from fundamental quantities.
• Examples:
  • Speed = Distance/Time
  • Force = Mass × Acceleration
  • Density = Mass/Volume

Thus, all physical quantities can be expressed using fundamental quantities.

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Q2. Explain the SI system of units.

Answer:

The SI system is the internationally accepted system of units.

The seven SI base units are:

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

The SI system ensures uniformity in measurements throughout the world.

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5. Assertion and Reason Questions

Q1.

Assertion (A): Speed is a derived quantity.

Reason (R): Speed is obtained by dividing distance by time.

Answer: Both A and R are true and R is the correct explanation of A.

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Q2.

Assertion (A): Length is a fundamental quantity.

Reason (R): Length can be expressed in terms of speed and time.

Answer: Assertion is true but Reason is false.

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Q3.

Assertion (A): Force is a derived quantity.

Reason (R): Force depends on mass and acceleration.

Answer: Both A and R are true and R is the correct explanation.

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6. Fill in the Blanks

1. Measurement involves comparison with a standard ________. Answer: unit

2. The SI unit of mass is ________. Answer: kilogram

3. The SI unit of length is ________. Answer: metre

4. Force is a ________ quantity. Answer: derived

5. A complete set of units is called a ________. Answer: system of units

6. Numerical value together with unit gives the result of a ________. Answer: measurement

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7. Statement-Based Questions

Q1. Identify whether the statements are True or False.

(a) Every physical quantity has a numerical value and a unit. Answer: True

(b) Speed is a fundamental quantity. Answer: False

(c) Derived units are obtained from base units. Answer: True

(d) Kilogram is the SI unit of mass. Answer: True

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Q2. Choose the correct statement.

(a) Force is a fundamental quantity. (b) Length is a derived quantity. (c) Mass is a fundamental quantity. (d) Speed is a fundamental quantity.

Answer: (c) Mass is a fundamental quantity.

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8. Match the Following

Column A	Column B
(A) Length	(i) kg
(B) Mass	(ii) m
(C) Time	(iii) s
(D) Force	(iv) N

Answer:

A → ii

B → i

C → iii

D → iv

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9. Case Study Questions

Case Study

A student measures the length of a table and finds it to be 2 m. Here, 2 is the numerical value and m is the unit. Measurement is the comparison of a physical quantity with a standard unit.

Questions

Q1. What is the measured physical quantity?

Answer: Length

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Q2. What is the numerical value?

Answer: 2

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Q3. What is the unit used?

Answer: Metre (m)

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Q4. Is length a fundamental or derived quantity?

Answer: Fundamental quantity

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Q5. Write the SI unit of length.

Answer: Metre (m)

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Important CBSE Exam Questions

1. Define measurement and unit.
2. What is a physical quantity?
3. Differentiate between fundamental and derived quantities.
4. What are derived units? Give examples.
5. Explain the SI system of units.
6. List the seven SI base units.
7. Why are standard units necessary?
8. Write the difference between base units and derived units.

 INTRODUCTION TO UNITS AND MEASUREMENT

│

├── Measurement

│   ├── Comparison of physical quantity

│   ├── Compared with standard reference

│   └── Gives numerical value + unit

│

├── Physical Quantity

│   ├── Can be measured

│   ├── Examples

│   │   ├── Length

│   │   ├── Mass

│   │   ├── Time

│   │   ├── Temperature

│   │   └── Force

│

├── Unit

│   ├── Standard reference for measurement

│   ├── Arbitrarily chosen

│   └── Internationally accepted

│

├── Result of Measurement

│   ├── Numerical Value (Number)

│   └── Unit

│       └── Example: 10 m

│           ├── 10 → Number

│           └── m → Unit

│

├── Physical Quantities

│   ├── Very large in number

│   ├── Inter-related with each other

│   └── Need only limited basic units

│

├── Fundamental (Base) Quantities

│   ├── Independent quantities

│   ├── Length

│   ├── Mass

│   ├── Time

│   ├── Electric Current

│   ├── Temperature

│   ├── Amount of Substance

│   └── Luminous Intensity

│

├── Fundamental (Base) Units

│   ├── Units of fundamental quantities

│   ├── Metre (m)

│   ├── Kilogram (kg)

│   ├── Second (s)

│   ├── Ampere (A)

│   ├── Kelvin (K)

│   ├── Mole (mol)

│   └── Candela (cd)

│

├── Derived Quantities

│   ├── Depend on fundamental quantities

│   ├── Speed = Distance / Time

│   ├── Force = Mass × Acceleration

│   └── Density = Mass / Volume

│

├── Derived Units

│   ├── Combination of base units

│   ├── Speed → m s⁻¹

│   ├── Force → kg m s⁻² (N)

│   └── Density → kg m⁻³

│

└── System of Units

    ├── Collection of base units

    ├── Collection of derived units

    └── SI System

        ├── Internationally accepted

        └── Contains 7 base units

NEET FORMULA

Physical 

 = Numerical Value × Unit 

Internal Links

Physical Quantities and Their Types

SI Units and Dimensions

Errors in Measurement

Significant Figures

Dimensional Analysis

Motion in One Dimension

Vectors and Scalars

Basic Mathematics for Physics

Kinematics Complete Notes

NEET Physics Formula Sheet

Physical Quantities & SI Units: Notes for CBSE Class 11 & NEET |

Understanding the fundamental building blocks of Physics: The 7 Base SI Units.

🔗 Internal Link 

 * To a Physics Chapter: "Now that you've mastered units, check out our guide on [Dimensional Analysis and Errors]."

 * To a Practical Guide: "Learn how these units apply in the laboratory with our [Class 11 Physics Practical Manual]."

 * To a Foundation Course: "New to high school physics? Start with [The Basics of Mathematical Tools in Physics]."

Units and Measurement

The Subatomic Scale: At the level of 10^-13 m, we enter the world of the atomic nucleus. This is the domain of Nucleons (Protons and Neutrons) and heavier elementary particles. These particles are bound together by the exchange of Gluons, the messengers of the strong nuclear force.

Physical Quantities

All quantities that can be measured are called physical quantities. In physics, we study these quantities and their inter-relationships (e.g., length, mass, force, work done).

Types of Physical Quantities

• Fundamental Quantity: Physical quantities which cannot be expressed in terms of any other physical quantities.
  Examples: Length, Mass, Time, Temperature.
• Derived Quantity: Physical quantities which are derived from fundamental quantities.
  Examples: Area, Density, Force.

Measurement

Measurement is the comparison of a physical quantity with a standard of the same physical quantity. A standard unit is essential for:

1. Accuracy
2. Convenience
3. Uniformity
4. Equal justice to all

Characteristics of a Standard Unit

A chosen unit should be: Consistent (Invariable), Available, Imperishable (Permanent), Convenient, and Reproducible.

Classification of Units

• Fundamental Unit: Used to measure fundamental quantities (e.g., Metre, Kilogram).
• Derived Unit: Used to measure derived quantities (e.g., Square metre for area, g/cm³ for density).

Systems of Units

System	Length	Mass	Time
FPS (British)	Foot (ft)	Pound (lb)	Second (s)
CGS (Gaussian)	Centimetre (cm)	Gram (g)	Second (s)
MKS	Metre (m)	Kilogram (kg)	Second (s)

International System of Units (SI)

The SI system is a modern modification of the MKS system. It is the most widely used system globally and consists of three categories:

• 7 Fundamental Quantities
• 2 Supplementary Quantities (Radian and Steradian)
• Derived Quantities

Physics: The Science of Measurement

Understanding the Subatomic Scale

When we talk about 10^-13 m to 10^-15 m, we are looking at the building blocks of matter:

• Nucleons: Protons and Neutrons (size approx. 0.8 x 10^-15 m).
• Gluons: The "glue" (massless particles) that hold quarks together within nucleons.
• Measurement Context: These are measured using Fermi (1 fm = 10^-15 m).

1. Physical Quantities

Anything that can be measured numerically and follows the laws of physics is a Physical Quantity.

Quantity	Type	Real-World Example / Relationship
Mass	Fundamental	Quantity of matter in an object (Scalar).
Length	Fundamental	Distance between two points.
Force	Derived	Mass × Acceleration (kg·m/s²).
Density	Derived	Mass / Volume (kg/m³).

Why do we need Standard Units?

Imagine buying cloth where the "meter" changed every day. Standards ensure:

• Invariability: The unit doesn't change with time or temperature.
• Reproducibility: A scientist in India and a scientist in Brazil get the same result.

2. Global Systems of Units

While the world has converged on SI Units, historical systems provide context for how we measure today:

System	Length	Mass	Time
FPS (British)	Foot (ft)	Pound (lb)	Second (s)
CGS (Gaussian)	Centimeter (cm)	Gram (g)	Second (s)
MKS (Standard)	Meter (m)	Kilogram (kg)	Second (s)

3. The SI System (Modern Standard)

The International System (SI) is the complete version of MKS. It includes:

• 7 Base Units: (Meter, Kilogram, Second, Ampere, Kelvin, Mole, Candela).
• 2 Supplementary Units: Radian (plane angle) and Steradian (solid angle).

Fundamental Quantities & SI Units

1. Comparison of Unit Systems

Physical Quantity	CGS (Gaussian)	MKS (Standard)	FPS (British)
Length	Centimetre (cm)	Metre (m)	Foot (ft)
Mass	Gram (g)	Kilogram (kg)	Pound (lb)
Time	Second (s)	Second (s)	Second (s)

2. The 7 Fundamental SI Units

The International System of Units (SI) is the modern form of the metric system. Below are the precise scientific definitions for the base units:

Length m

Unit: Metre

The distance traveled by light in vacuum in 1/299,792,458 of a second.

Mass kg

Unit: Kilogram

Defined by the mass of a platinum-iridium cylinder kept at the International Bureau of Weights and Measures.

Time s

Unit: Second

The duration of 9,192,631,770 periods of radiation from the transition between two hyperfine levels of Cesium-133.

Thermodynamic Temp. K

Unit: Kelvin

The fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

Electric Current A

Unit: Ampere

The constant current which produces a force of 2 × 10⁻⁷ N/m between two parallel conductors of infinite length.

Luminous Intensity cd

Unit: Candela

The intensity of a blackbody of surface area 1m² at the temperature of freezing platinum under standard pressure.

Amount of Substance mol

Unit: Mole

The amount of substance containing as many elementary entities as there are atoms in 0.012 kg of carbon-12.

3. Supplementary Quantities

1. Plane Angle (Radian - rad): Defined as θ = arc / radius.

2. Solid Angle (Steradian - sr): Defined as Ω = Area / (Radius)².

Practice Module: Units & Measurement

Target: CBSE Class 11 & NEET 2026

Section A: Very Short Answer (1 Mark)

Q1. Define a Light Year.

View Solution

It is the distance traveled by light in vacuum in one year. 1 ly = 9.46 × 10¹⁵ m.

Section B: Multiple Choice Questions NEET Pattern

Q2. Which of the following is NOT a fundamental SI unit?

• (A) Ampere
• (B) Candela
• (C) Newton
• (D) Kelvin

View Solution

Correct Option: (C). Newton is a derived unit (kg·m/s²), while Ampere, Candela, and Kelvin are fundamental units.

Section C: Assertion & Reason

Directions: (A) Both A and R are true and R is the correct explanation. (B) Both A and R are true, but R is not the correct explanation. (C) A is true, R is false. (D) A is false, R is true.

Assertion (A): Light year and year, both measure time.
Reason (R): Because both have "year" in their name.

View Solution

Correct Option: (D). Assertion is false because Light Year is a unit of Distance, not time. Reason is true as a statement of naming, but does not justify the physics.

Section D: Descriptive Questions (3 & 5 Marks)

Q3. Distinguish between Fundamental and Derived units with two examples each.

View Solution

Fundamental Units: Independent units like Metre (m) and Kilogram (kg).
Derived Units: Units expressed in terms of base units, like Velocity (m/s) or Force (N).

Q4. State the characteristics of a standard unit of measurement. (Long Answer)

View Solution

A standard unit should be:

1. Invariable: It should not change with time or physical conditions.
2. Available: It should be easily accessible.
3. Reproducible: It can be recreated anywhere in the world.
4. Indestructible: It should be permanent.

Physical Quantities & Measurement

Comprehensive Question Bank for Class 11 Physics

CBSE PATTERN NEET PREP

I. Very Short Answer Questions (1 Mark)

1. What is meant by a "Physical Quantity"?

View Solution

All quantities that can be measured, either directly or indirectly, and in terms of which the laws of physics can be described are called physical quantities. Examples: Length, Mass, Force.

2. Distinguish between Fundamental and Derived quantities.

View Solution

Fundamental: Quantities that cannot be expressed in terms of others (e.g., Time, Temperature).
Derived: Quantities derived from fundamental ones (e.g., Area = Length × Breadth).

II. Multiple Choice Questions (NEET Pattern)

3. Which of the following is the fundamental unit in the FPS system for Mass?

• A) Gram
• B) Kilogram
• C) Pound
• D) Slug

View Solution

Correct Answer: C (Pound). In the FPS (British Engineering) system, the base units are Foot (length), Pound (mass), and Second (time).

4. The International System of Units (SI) is a modification of which system?

• A) FPS
• B) CGS
• C) MKS
• D) Gaussian

View Solution

Correct Answer: C (MKS). SI is an improved and extended version of the MKS system, including seven base and two supplementary units.

III. Assertion & Reason

Instructions:
(A) Both A and R are true and R is the correct explanation of A.
(B) Both A and R are true but R is NOT the correct explanation of A.
(C) A is true but R is false.
(D) A is false but R is true.

Assertion (A): Measurement is essentially a process of comparison.
Reason (R): A standard unit should be easily reproducible and invariable.

View Solution

Correct Answer: B. Both statements are factually correct. However, the reason (characteristics of a unit) does not explain the definition of measurement (the process of comparison).

IV. Long Answer Questions (5 Marks)

5. What are the essential characteristics of a standard unit? Why is SI preferred globally?

View Solution

Characteristics:

1. Invariability: It must not change with time or physical conditions (temperature, pressure).
2. Availability: It should be easily available for comparison.
3. Reproducibility: It should be possible to replicate the standard anywhere.
4. Permanency: It should not be perishable.

Why SI is Preferred: It is a coherent and rational system of units used worldwide, ensuring uniformity in scientific data exchange and international trade.

Quick Review: Unit Systems

System	Length	Mass	Time
CGS	cm	g	s
MKS	m	kg	s
FPS	ft	lb	s