NCERT Solutions for Class 11 Physics Chapter 1 Units and Measurements - FREE PDF Download
FAQs on NCERT Solutions for Class 11 Physics Chapter 1 Units and Measurements
1. What do the NCERT Solutions for Class 11 Physics Chapter 1 provide for the 2025-26 session?
The NCERT Solutions for Class 11 Physics Chapter 1, Units and Measurements, provide detailed, step-by-step answers for all the exercise questions in the textbook. They are fully updated for the CBSE 2025-26 syllabus and focus on explaining the correct method for solving problems related to dimensional analysis, error calculation, and significant figures.
2. How do you solve problems involving unit conversion using the method in NCERT Solutions?
The correct method, as shown in the NCERT solutions, involves using dimensional analysis. The steps are:
- Identify the given physical quantity and its current units.
- Write down the dimensional formula for the quantity (e.g., Force is [MLT⁻²]).
- Determine the conversion factors between the old and new base units (e.g., 1 m = 100 cm).
- Substitute the conversion factors into the dimensional formula and calculate the new numerical value.
3. What are the key rules for determining significant figures in a measurement as per the Class 11 Physics Chapter 1 solutions?
The NCERT solutions for Chapter 1 clarify the following rules for significant figures:
- All non-zero digits are significant.
- Zeros between two non-zero digits are significant (e.g., 6.032 has 4 significant figures).
- Leading zeros (zeros before non-zero digits) are not significant (e.g., 0.007 has 1 significant figure).
- Trailing zeros in a number with a decimal point are significant (e.g., 6.320 has 4 significant figures).
4. How are different types of errors in measurement classified in the NCERT exercises?
In Chapter 1, measurement errors are primarily classified into two types:
- Systematic errors: These are consistent, directional errors due to instrument flaws (like a zero error) or incorrect experimental procedures. They can often be minimized.
- Random errors: These are unpredictable, non-directional errors caused by unknown factors or limitations of the observer. They can be reduced by taking multiple readings and averaging them.
5. Why is using the SI system of units recommended in the NCERT Solutions for solving Physics problems?
The SI (Système International) system is a coherent and rationalised system of units. Using SI units, as emphasised in the NCERT Solutions, is crucial because it standardises calculations, prevents conversion mistakes, and ensures consistency across different topics in physics. This is the standard for CBSE exams and scientific communication worldwide, making it easier to derive and check equations.
6. What happens if a physical equation is not dimensionally homogeneous?
If an equation is not dimensionally homogeneous, it means the dimensions on the left-hand side do not match the dimensions on the right-hand side. According to the principle of homogeneity, such an equation is fundamentally incorrect. For example, you cannot add a quantity with the dimension of length [L] to one with the dimension of time [T]. Spotting this indicates an error in the formula's derivation or application.
7. What is the step-by-step approach to checking the dimensional correctness of a formula like Einstein's mass-energy relation?
To check an equation's dimensional correctness, as done in the NCERT solutions, follow these steps:
- Step 1: Write down the dimensional formula for the quantity on the Left Hand Side (LHS).
- Step 2: Write down the dimensional formula for all terms on the Right Hand Side (RHS).
- Step 3: Apply the principle of homogeneity. The dimensions of the LHS must equal the dimensions of the RHS.
- Step 4: For a relation like m = m₀ / √(1-v²/c²), you ensure that the term v²/c² is dimensionless, as it is subtracted from a dimensionless number (1).
8. How do the NCERT Solutions explain the difference between accuracy and precision in measurement?
The solutions clarify that:
- Accuracy refers to how close a measured value is to the true or accepted value of the quantity.
- Precision refers to how close multiple measurements of the same quantity are to each other, indicating the resolution or limit of the measuring instrument.
9. Why can't dimensional analysis determine the value of dimensionless constants in a formula?
Dimensional analysis is a powerful tool for checking consistency and deriving relationships between physical quantities, but it has limitations. It cannot determine dimensionless constants (like 'k', π, or 1/2) because these constants do not have physical dimensions. Their values must be found through experimentation or more advanced theoretical derivation, which is a key concept explained through problems in the NCERT solutions.
10. Why is it meaningless to call a quantity 'large' or 'small' without a standard for comparison, as explained in an NCERT problem?
Describing a physical quantity as 'large' or 'small' is relative and lacks scientific meaning without a reference point. For instance, the mass of Jupiter is 'large' compared to the mass of Earth, but 'small' compared to the mass of the Sun. The NCERT solutions stress that for a description to be meaningful, you must specify what it is being compared to, establishing a clear standard of comparison.
11. How does taking more measurements improve the reliability of an estimate, like measuring the diameter of a rod?
Taking a larger number of measurements helps to minimise the effect of random errors. Individual random errors can be positive or negative. When you take the arithmetic mean of many observations (e.g., 100 measurements instead of 5), these random positive and negative errors tend to cancel each other out. This makes the final average value a more reliable and accurate estimate of the true value, a key practical skill covered in the NCERT exercises.
12. How should a student use these NCERT Solutions to master numerical problems for their Class 11 exams?
For effective exam preparation, students should first attempt to solve the NCERT exercise problems independently. Afterwards, use these solutions to:
- Verify the final answer.
- Understand the correct step-by-step method if you are stuck.
- Identify and learn from mistakes in applying formulas or performing unit conversions.
- Pay close attention to how significant figures and error propagation are handled in the final answers, as marks are often allocated for these steps in CBSE exams.

















