📘 Class 11 Maharashtra Board Physics Chapter 1: Units and Measurements Study Guide

Chapter 1: Units and Measurements is the foundation of physics. Everything you study in physics, from motion to electricity, begins with the precise measurement of quantities. This chapter introduces you to physical quantities, systems of units, and measurement tools. You’ll also learn about accuracy, errors, and dimensional analysis — concepts that are vital in all scientific work.

Let’s dive into a detailed study guide for mastering this chapter.

🔍 1. Introduction to Physical Quantities

In physics, physical quantities are those that can be measured and expressed in numbers. They are classified into:

• Fundamental quantities: Cannot be broken down (e.g., mass, length, time)
• Derived quantities: Formed by combining fundamental ones (e.g., speed = distance/time)

📏 2. Systems of Units

Units are the standard for measuring physical quantities. There are various systems of units:

• CGS (Centimeter-Gram-Second)
• FPS (Foot-Pound-Second)
• MKS (Meter-Kilogram-Second)
• SI (International System of Units) – Globally accepted

📐 3. Measurement of Physical Quantities

To measure any quantity accurately:

• Use the right instrument
• Calibrate the instrument
• Understand the least count (smallest measurable value)

Common instruments:

• Vernier caliper (length)
• Screw gauge (small thickness)
• Stopwatch (time)

🧮 4. Accuracy, Precision & Errors

Measurements always include some errors. Understanding these errors helps improve accuracy.

Types of Errors:

1. Systematic errors: Due to faulty equipment or technique. These are consistent.
2. Random errors: Due to unknown fluctuations. These vary.
3. Gross errors: Human mistakes, e.g., misreading.

Absolute Error:

Difference between measured value and true value.

Relative Error:

Relative error= Absolute Error​/True Value

Percentage Error:Relative Error×100/1

tips

• Take multiple readings and average them.
• Use high-precision instruments.

📊 5. Significant Figures

Significant figures reflect the precision of a measurement. They include:

• All non-zero digits
• Zeros between non-zero digits
• Trailing zeros only if there's a decimal

Rules:

• While adding/subtracting: Answer should match the least number of decimal places.
• While multiplying/dividing: Match the least number of significant figures.

Example:

3.142×2.1=6.63.142 \times 2.1 = 6.63.142×2.1=6.6 (2 significant figures)

🧠 6. Dimensional Analysis

Dimensions express physical quantities in terms of base quantities.

Dimensional Formula:

It expresses a physical quantity using symbols:

Length – [L], Mass – [M], Time – [T]

Applications:

1. Checking the correctness of equations (Principle of Homogeneity)
2. Converting units
3. Deriving relations among quantities

Example:

Verify the formula v=u+at

Both sides have the dimension:[LT−1] So it's dimensionally correct.

🧪 7. Practical Use of Units and Measurements

In real-world physics labs, the correct measurement technique makes a big difference.

Common Experiments:

• Measuring diameter using Vernier caliper
• Finding thickness of a wire using screw gauge
• Time period of a pendulum with a stopwatch

Each experiment involves:

• Least count calculation
• Multiple readings
• Error analysis

🎯 8. Exam Preparation Tips

1. Understand Definitions: Be clear about the difference between precision, accuracy, and error.
2. Memorize SI Units: Ensure you know all 7 base units.
3. Practice Numerical Problems: Especially on error calculations and unit conversions.
4. Revise Dimensional Formulas: Many 2-mark questions are based on this.
5. Use Flashcards: For quick recall of formulas and rules.

🧠 9. Sample Questions

1. Define absolute error. How is it different from relative error?
2. State SI base units and their symbols.
3. Use dimensional analysis to check if s=ut+12at2s = ut + \frac{1}{2}at^2s=ut+21​at2 is correct.
4. Convert 1 N into CGS units using dimensional method.
5. A screw gauge has a pitch of 0.5 mm and 50 divisions on the circular scale. Find the least count.

✅ 10. Final Thoughts

Chapter 1: Units and Measurements is not just theoretical. It gives you tools you will use in every single chapter of physics. From calculating acceleration in motion to understanding pressure in fluids — everything depends on accurate measurement and correct units.

Take this chapter seriously, build a strong base, and your entire journey through Class 11 and 12 physics will be easier.