Introduction to Units and Measurement (NEET Level – Easy Notes)
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| Introduction to Units and Measurement – Complete NEET Physics Mind Map and Quick Revision Notes. |
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:
- Numerical value (number)
- 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 |
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
Q2. The internationally accepted standard for measurement is called:
(a) Scale
(b) Instrument
(c) Unit
(d) Quantity
Answer: (c) Unit
Q3. Which of the following is a fundamental quantity?
(a) Force
(b) Speed
(c) Length
(d) Density
Answer: (c) Length
Q4. Which of the following is a derived quantity?
(a) Mass
(b) Time
(c) Temperature
(d) Force
Answer: (d) Force
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
Q7. Which is NOT a fundamental quantity?
(a) Length
(b) Mass
(c) Time
(d) Speed
Answer: (d) Speed
Q8. A complete set of units is called:
(a) Physical quantity
(b) Standard
(c) System of units
(d) Measurement
Answer: (c) System of units
2. Very Short Answer Questions (1 Mark)
Q1. What is measurement?
Answer: Measurement is the comparison of a physical quantity with a standard unit.
Q2. Define unit.
Answer: A unit is a fixed standard used for measuring a physical quantity.
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.
Q5. Write the SI unit of time.
Answer: Second (s).
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:
- Length
- Mass
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 |
Q3. What are derived units? Give two examples.
Answer: Units obtained by combining fundamental units are called derived units.
Examples:
- Speed = m/s
- Force = kg m s⁻²
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.
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.
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.
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.
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.
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.
6. Fill in the Blanks
Measurement involves comparison with a standard ________. Answer: unit
The SI unit of mass is ________. Answer: kilogram
The SI unit of length is ________. Answer: metre
Force is a ________ quantity. Answer: derived
A complete set of units is called a ________. Answer: system of units
Numerical value together with unit gives the result of a ________. Answer: measurement
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
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.
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
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
Q2. What is the numerical value?
Answer: 2
Q3. What is the unit used?
Answer: Metre (m)
Q4. Is length a fundamental or derived quantity?
Answer: Fundamental quantity
Q5. Write the SI unit of length.
Answer: Metre (m)
Important CBSE Exam Questions
- Define measurement and unit.
- What is a physical quantity?
- Differentiate between fundamental and derived quantities.
- What are derived units? Give examples.
- Explain the SI system of units.
- List the seven SI base units.
- Why are standard units necessary?
- 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
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