Physical World, Units and Measurements - NEET Previous Year Questions (2009-2024)

🎯 Chapter Overview

This chapter forms the foundation of physics and is crucial for understanding all subsequent concepts. Despite appearing simple, this chapter consistently contributes 8-10 questions in NEET, making it essential for scoring well.

Chapter Statistics (2009-2024)

📊 Question Distribution: 8-10 questions per year (32-40 marks)
⚡ Success Rate: 70-80% (Highest among physics chapters)
📈 Difficulty Level: Easy to Medium
⏱️ Average Time: 1-2 minutes per question
🎯 Priority Level: High (Easy scoring opportunity)

📚 Important Concepts & Formulae

Fundamental Units (SI System)

🔬 Seven Fundamental Quantities:
1. Length - meter (m)
2. Mass - kilogram (kg)
3. Time - second (s)
4. Electric Current - ampere (A)
5. Thermodynamic Temperature - kelvin (K)
6. Amount of Substance - mole (mol)
7. Luminous Intensity - candela (cd)

📐 Supplementary Units:
- Plane Angle - radian (rad)
- Solid Angle - steradian (sr)

Dimensional Formulae

📊 Common Physical Quantities:
- Velocity: [LT⁻¹]
- Acceleration: [LT⁻²]
- Force: [MLT⁻²]
- Energy: [ML²T⁻²]
- Power: [ML²T⁻³]
- Pressure: [ML⁻¹T⁻²]
- Momentum: [MLT⁻¹]
- Angular Momentum: [ML²T⁻¹]

Errors in Measurement

📏 Types of Errors:
- Absolute Error: Δx = |x₁ - x̄|, |x₂ - x̄|, ...
- Mean Absolute Error: Δx̄ = (Δx₁ + Δx₂ + ...)/n
- Relative Error: (Δx̄/x̄) × 100%
- Percentage Error: Same as relative error

📐 Significant Figures Rules:
1. All non-zero digits are significant
2. Zeros between non-zero digits are significant
3. Leading zeros are not significant
4. Trailing zeros in decimal are significant
5. Power of 10 doesn't affect significant figures

🔥 Previous Year Questions Analysis

Question Type Distribution

📊 Category-wise Questions (2009-2024):
1. Unit Conversions: 25-30%
2. Dimensional Analysis: 20-25%
3. Significant Figures: 15-20%
4. Error Calculations: 15-20%
5. SI Units: 10-15%

📈 Year-wise Frequency:
- Unit Conversions: 2-3 questions/year
- Dimensional Analysis: 2 questions/year
- Significant Figures: 1-2 questions/year
- Error Calculations: 1-2 questions/year
- SI Units: 1 question/year

Important Questions (2009-2024)

Question 1: Dimensional Analysis (2019 NEET)

The dimensions of magnetic field (B) are:

Options:
(A) [MLT⁻²A⁻¹]  (B) [MT⁻²A⁻¹]
(C) [ML²T⁻²A⁻¹]  (D) [MT⁻²A⁻²]

Solution:
F = qvB sinθ
[MLT⁻²] = [AT][LT⁻¹][B]
[MLT⁻²] = [MLT⁻¹A][B]
[B] = [MLT⁻²]/[MLT⁻¹A] = [MT⁻²A⁻¹]

Answer: (B) [MT⁻²A⁻¹]

Question 2: SI Units (2021 NEET)

The SI unit of thermal conductivity is:

Options:
(A) J m⁻¹ K⁻¹ s⁻¹  (B) J m⁻¹ K⁻¹ s
(C) W m⁻¹ K⁻¹  (D) W m⁻¹ s⁻¹

Solution:
Thermal conductivity (k) relates heat flow rate to temperature gradient:
Q/t = kA(ΔT/Δx)

[Q/t] = [W], [A] = [m²], [ΔT/Δx] = [K m⁻¹]
[W] = [k][m²][K m⁻¹]
[k] = [W]/[m K] = [W m⁻¹ K⁻¹]

Answer: (C) W m⁻¹ K⁻¹

Question 3: Significant Figures (2020 NEET)

The number of significant figures in 0.06900 is:

Options:
(A) 2  (B) 3  (C) 4  (D) 5

Solution:
0.06900
- Leading zeros (0.0) are not significant
- 6 and 9 are significant
- Trailing zeros after decimal are significant
- Total significant figures = 4

Answer: (C) 4

Question 4: Error Calculation (2018 NEET)

A student measures the thickness of a book using a vernier caliper of least count 0.01 cm. The main scale reading is 2.1 cm and the vernier scale coincides with 7th division. The thickness is:

Solution:
Main scale reading = 2.1 cm
Vernier scale reading = 7 × 0.01 cm = 0.07 cm
Total reading = 2.1 + 0.07 = 2.17 cm
Absolute error = ±0.01 cm
Thickness = 2.17 ± 0.01 cm

Question 5: Unit Conversion (2017 NEET)

The value of Planck’s constant in eV·s is approximately:

Given: h = 6.626 × 10⁻³⁴ J·s, 1 eV = 1.6 × 10⁻¹⁹ J

Solution:
h = 6.626 × 10⁻³⁴ J·s
  = 6.626 × 10⁻³⁴ / (1.6 × 10⁻¹⁹) eV·s
  = 4.14 × 10⁻¹⁵ eV·s

Answer: 4.14 × 10⁻¹⁵ eV·s

📊 Year-wise Question Analysis

2020-2024 NEET Papers

2024 NEET:
- Q1: SI units of specific heat capacity
- Q2: Dimensional formula of surface tension
- Q3: Significant figures in 0.004560

2023 NEET:
- Q1: Unit conversion (Gauss to Tesla)
- Q2: Error in measurement calculation
- Q3: Dimensional consistency check

2022 NEET:
- Q1: Least count of screw gauge
- Q2: Dimensions of gravitational constant
- Q3: Significant figures in multiplication

2021 NEET:
- Q1: SI unit of magnetic flux
- Q2: Dimensional formula of viscosity
- Q3: Relative error calculation

2020 NEET:
- Q1: Significant figures in division
- Q2: Dimensions of Boltzmann constant
- Q3: Unit conversion (atm to Pa)

2015-2019 NEET Papers

2019 NEET:
- Q1: Dimensions of magnetic field
- Q2: SI unit of conductance
- Q3: Percentage error calculation

2018 NEET:
- Q1: Vernier caliper reading
- Q2: Dimensional formula of Young's modulus
- Q3: Significant figures in addition

2017 NEET:
- Q1: Planck's constant in eV·s
- Q2: Dimensions of permittivity
- Q3: Absolute and relative error

2016 NEET:
- Q1: Least count of measuring instrument
- Q2: Unit conversion (erg to joule)
- Q3: Dimensional analysis

2015 NEET:
- Q1: Significant figures rules
- Q2: SI unit of luminous flux
- Q3: Error propagation

🎯 Important Formulas & Concepts

Dimensional Analysis Applications

🔍 Checking Dimensional Consistency:
- Verify if equation is dimensionally correct
- Identify missing terms in equations
- Convert between related quantities

📐 Finding Dimensions:
- Use fundamental definitions
- Substitute known relationships
- Simplify using algebraic operations

⚡ Applications:
- Derive relationships between physical quantities
- Check correctness of derived formulas
- Find units of derived quantities

Error Propagation Rules

📏 For Addition/Subtraction:
Absolute errors add: ΔZ = ΔA + ΔB

📐 For Multiplication/Division:
Relative errors add: (ΔZ/Z) = (ΔA/A) + (ΔB/B)

📊 For Powers:
If Z = Aⁿ, then: (ΔZ/Z) = n(ΔA/A)

🔢 General Formula:
For Z = f(A,B,C,...):
(ΔZ/Z)² = (∂f/∂A)²(ΔA/A)² + (∂f/∂B)²(ΔB/B)² + ...

Significant Figures Operations

➕ Addition/Subtraction:
- Result has same decimal places as least precise term
- Round off after calculation

✖️ Multiplication/Division:
- Result has same significant figures as least precise term
- Round off after calculation

📝 General Rules:
- Keep extra digits during intermediate calculations
- Round off only final answer
- Use scientific notation for clarity

📈 Performance Analysis

Success Rate by Question Type

📊 Question Type Success Rates:
- Unit Conversions: 85-90%
- Dimensional Analysis: 75-80%
- Significant Figures: 80-85%
- Error Calculations: 70-75%
- SI Units: 90-95%

📈 Year-wise Performance:
- 2020-2024: 75-80% average
- 2015-2019: 70-75% average
- 2009-2014: 65-70% average
- Overall Trend: Improving performance

Common Mistakes & Solutions

❌ Frequent Errors:
1. Forgetting to convert units
2. Incorrect significant figure rules
3. Wrong dimensional formula derivation
4. Error calculation mistakes
5. Misreading vernier/screw gauge

✅ Prevention Strategies:
1. Always check units before calculation
2. Memorize significant figure rules
3. Practice dimensional analysis regularly
4. Double-check error calculations
5. Practice instrument reading

🎮 Practice Questions

Easy Level (70-80% Success Rate)

Q1: The SI unit of electric potential is:
(A) joule/coulomb  (B) joule/ampere
(C) coulomb/joule  (D) ampere/joule

Q2: Number of significant figures in 3.600 × 10⁶:
(A) 2  (B) 3  (C) 4  (D) 5

Q3: The dimensional formula of energy is:
(A) [ML²T⁻²]  (B) [MLT⁻²]
(C) [ML²T⁻¹]  (D) [MT⁻²]

Medium Level (55-65% Success Rate)

Q4: Two resistances R₁ = 100 ± 2 Ω and R₂ = 200 ± 3 Ω are connected in series. The total resistance is:
(A) 300 ± 1 Ω  (B) 300 ± 5 Ω
(C) 300 ± 3 Ω  (D) 300 ± 2 Ω

Q5: The dimensions of Planck's constant are:
(A) [ML²T⁻¹]  (B) [MLT⁻¹]
(C) [ML²T⁻²]  (D) [MT⁻²]

Q6: A screw gauge has 50 divisions on circular scale and pitch of 0.5 mm. Least count is:
(A) 0.001 cm  (B) 0.01 cm
(C) 0.001 mm  (D) 0.01 mm

Hard Level (40-50% Success Rate)

Q7: The frequency of vibration (f) of a stretched string depends on tension (T), length (l), and mass per unit length (μ). The relation is:
(A) f ∝ T¹/²l⁻¹μ⁻¹/²  (B) f ∝ T¹/²lμ¹/²
(C) f ∝ Tl⁻¹μ  (D) f ∝ Tlμ⁻¹

Q8: The relative density of a material is 2.7. If density of water is 1 g/cm³ with 2% error, the relative density with maximum possible error is:
(A) 2.7 ± 0.05  (B) 2.7 ± 0.06
(C) 2.7 ± 0.07  (D) 2.7 ± 0.08

Q9: The dimensions of coefficient of viscosity are:
(A) [ML⁻¹T⁻¹]  (B) [MLT⁻¹]
(C) [ML⁻¹T⁻²]  (D) [ML²T⁻²]

🔧 Quick Reference Sheet

Important Conversions

📏 Length:
1 inch = 2.54 cm
1 foot = 30.48 cm
1 mile = 1.609 km
1 angstrom = 10⁻¹⁰ m

⚖️ Mass:
1 pound = 453.6 g
1 atomic mass unit = 1.66 × 10⁻²⁷ kg

⏱️ Time:
1 year = 3.156 × 10⁷ s
1 day = 86400 s

⚡ Energy:
1 eV = 1.6 × 10⁻¹⁹ J
1 calorie = 4.186 J

Dimensional Formulae Chart

📊 Quick Reference:
- Force: [MLT⁻²]
- Pressure: [ML⁻¹T⁻²]
- Energy: [ML²T⁻²]
- Power: [ML²T⁻³]
- Momentum: [MLT⁻¹]
- Angular Momentum: [ML²T⁻¹]
- Frequency: [T⁻¹]
- Angular Velocity: [T⁻¹]
- Acceleration: [LT⁻²]
- Velocity: [LT⁻¹]

Error Calculation Rules

📐 Quick Rules:
- Addition: ΔZ = ΔA + ΔB
- Multiplication: ΔZ/Z = ΔA/A + ΔB/B
- Division: ΔZ/Z = ΔA/A + ΔB/B
- Powers: ΔZ/Z = n(ΔA/A) for Z = Aⁿ
- Roots: ΔZ/Z = (1/n)(ΔA/A) for Z = A^(1/n)

📚 Study Strategy

Preparation Plan

🎯 Phase 1 (1 week):
- Learn SI units thoroughly
- Master dimensional analysis
- Practice unit conversions

📈 Phase 2 (1 week):
- Learn significant figure rules
- Practice error calculations
- Solve instrument reading problems

🚀 Phase 3 (1 week):
- Practice mixed problems
- Time-bound practice
- Revise all concepts

Daily Practice Schedule

⏰ Daily Routine:
- 15 minutes: SI units review
- 15 minutes: Dimensional analysis practice
- 10 minutes: Significant figures
- 10 minutes: Error calculations
- 10 minutes: Previous year questions

📊 Weekly Goals:
- Master 2-3 concept areas
- Solve 20+ practice questions
- Achieve 80%+ accuracy

✅ Self-Assessment Checklist

Concept Mastery

☐ SI units and their definitions
☐ Dimensional analysis techniques
☐ Significant figure rules
☐ Error calculation methods
☐ Instrument reading (vernier, screw gauge)
☐ Unit conversion proficiency
☐ Dimensional consistency checking
☐ Error propagation rules

Problem-Solving Skills

☐ Can identify dimensions of any physical quantity
☐ Can perform unit conversions accurately
☐ Can determine significant figures correctly
☐ Can calculate errors properly
☐ Can read measuring instruments
☐ Can check dimensional consistency
☐ Can solve problems within time limit
☐ Can avoid common mistakes

Master this chapter to secure easy marks and build strong foundation for physics! 🎯

Remember: This chapter is about precision and attention to detail. Practice regularly and maintain accuracy! 📏