Important MCQs and Answers for Units and Measurements in Physics Class 11
The topic of Class 11 Physics MCQs Chapter 2 Units and Measurements is important in physics and helps us understand the foundation of all physical quantities, how to conduct precise measurements, and solve calculation-based problems often seen in CBSE, JEE, and NEET exams.
Understanding Class 11 Physics MCQs Chapter 2 Units and Measurements
Units and Measurements refers to the standard methods and systems used to quantify physical quantities. In this chapter, you learn about fundamental and derived units, SI system, dimensional analysis, significant figures, and errors in measurement. Mastery of these concepts enables students to answer multiple choice questions confidently, analyze formulas, and avoid mistakes in physical calculations.
Formula or Working Principle of Units and Measurements
Key formulas in this chapter include dimensional analysis (checking or deriving equations), conversion of units, and application of significant figures. For any physical quantity Q:
Dimensional formula helps in verifying equations (e.g., [M1L2T-2] for energy).
Here’s a useful table to understand Units and Measurements better:
Units and Measurements Table
| Concept | Description | Example |
|---|---|---|
| Fundamental Unit | Base unit defined for a fundamental quantity | Metre (length), Kilogram (mass) |
| Derived Unit | Combines two or more fundamental units | Newton (kg·m/s2) |
| Dimensional Formula | Represents physical quantity in terms of fundamental quantities | Force: [M1L1T-2] |
| Significant Figures | Digits that carry meaning for measurement precision | 3 in 2.54 cm |
Worked Example / Practical Experiment
Let’s solve a problem step by step based on conversion of units:
1. Known: Distance = 1000 m; Convert to km.
2. Formula: 1 km = 1000 m
3. Calculation: Distance = 1000 m × (1 km / 1000 m) = 1 km
Conclusion: Knowing the right conversion factor and method allows precise conversion and helps avoid mistakes in exams.
Practice Questions
- Define units and measurements with one suitable example.
- How is dimensional analysis useful in checking the correctness of equations?
- Convert 1800 seconds to hours using the correct unit conversion method.
- State the SI units of force, energy, and pressure.
- How many significant figures are there in 0.00560?
- Write the dimensional formula for power.
Common Mistakes to Avoid
- Confusing the difference between fundamental and derived units.
- Using wrong conversion factors during unit conversion.
- Incorrectly counting significant figures (ignoring leading zeros).
- Mixing up physical quantities with similar units (like energy and work).
- Neglecting dimensions while solving numericals or verifying equations.
Real-World Applications
Units and Measurements are the backbone of scientific research, engineering designs, medical instruments, and even everyday tasks like weather forecasting. Accurate measurements ensure reliable experiments and correct application of physics laws. Vedantu makes this chapter easy by guiding you through solved MCQs, so you can apply concepts in various fields including technology, environment, and industry.
In this article, we explored Class 11 Physics MCQs Chapter 2 Units and Measurements — its meaning, formulas, common MCQ traps, and practical examples. Keep practicing with Vedantu and explore related topics for a stronger foundation in physics.
Explore further with these helpful pages:
- Accuracy, Precision, Error & Measurement
- Fundamental and Derived Units of Measurement
- SI Units List
- Conversion of Units
- Dimensional Analysis
- Significant Figures, Exact Numbers
- Measurement of Length, Distance
- Standard Units of Measurements
FAQs on Class 11 Physics MCQs on Units and Measurements – Chapter 2 Practice
1. What is the difference between a fundamental unit and a derived unit in Physics?
A fundamental unit is a standard unit for measuring a base physical quantity that is independent of other quantities. For example, the metre (m) for length. A derived unit is formed by combining fundamental units to measure a derived physical quantity. For example, the unit for speed is metres per second (m/s), which is derived from the fundamental units of length and time.
2. What are the seven fundamental quantities and their corresponding SI units as per the NCERT syllabus for Class 11?
As per the internationally accepted SI system for the 2025-26 syllabus, the seven fundamental physical quantities and their units are:
- Length - metre (m)
- Mass - kilogram (kg)
- Time - second (s)
- Electric Current - ampere (A)
- Thermodynamic Temperature - kelvin (K)
- Amount of Substance - mole (mol)
- Luminous Intensity - candela (cd)
3. How does dimensional analysis help in checking the correctness of a physical equation like v = u + at?
Dimensional analysis helps verify the principle of homogeneity, which states that all terms in a correct physical equation must have the same dimensions. To check v = u + at:
- Dimension of final velocity (v) = [LT⁻¹]
- Dimension of initial velocity (u) = [LT⁻¹]
- Dimension of acceleration × time (at) = [LT⁻²] × [T] = [LT⁻¹]
Since the dimensions of all three terms are identical ([LT⁻¹]), the equation is dimensionally correct.
4. Why are dimensions and units not the same thing, and how can confusing them lead to errors in MCQs?
Dimensions and units are related but distinct concepts. A dimension describes the fundamental nature of a physical quantity (e.g., length has the dimension [L]). A unit is the specific, standard measure used to quantify that dimension (e.g., metre, foot, inch). Confusing them can lead to errors in MCQs, especially in unit conversion problems or when identifying the correct dimensional formula, as a single dimension can be expressed in many different units.
5. What are the key rules for determining the number of significant figures in a measurement?
The key rules for determining significant figures are:
- All non-zero digits are significant.
- Zeros between two non-zero digits are significant (e.g., 205 has 3 significant figures).
- Leading zeros (zeros before non-zero digits) are not significant (e.g., 0.005 has 1 significant figure).
- Trailing zeros in a number without a decimal point are ambiguous, but in a number with a decimal point, they are significant (e.g., 2.500 has 4 significant figures).
6. What is the practical importance of significant figures when solving numerical problems in an exam?
The practical importance of significant figures is to reflect the precision of a measurement. In calculations, your final answer cannot be more precise than the least precise measurement used. In exams, especially in MCQs, answer options may differ only in their last digits. Using the correct rules for significant figures during addition, subtraction, multiplication, and division is crucial to select the most accurate answer and avoid losing marks.
7. What is the principle of homogeneity of dimensions and how is it applied?
The principle of homogeneity of dimensions states that a physically valid equation must have the same dimensions for every term on both sides of the equation. It is applied to:
- Check the dimensional correctness of a formula.
- Derive relationships between physical quantities.
For example, in the equation for work, W = Fd, the dimension of work [ML²T⁻²] must equal the dimensions of force [MLT⁻²] multiplied by distance [L], which is [ML²T⁻²].
8. Besides checking equations, what are the other two key applications of dimensional analysis for a Class 11 student?
Beyond just verifying the correctness of an equation, dimensional analysis has two other critical applications as per the Class 11 Physics syllabus:
- Deriving relationships: It helps in deducing the formula for a physical quantity by relating it to other quantities on which it might depend.
- Unit conversion: It provides a systematic method to convert the value of a physical quantity from one system of units (e.g., SI) to another (e.g., CGS).
9. How do you convert a physical quantity from one system of units to another using dimensional analysis?
To convert a quantity, you use the relationship n₁u₁ = n₂u₂, where n₁ and n₂ are the numerical values and u₁ and u₂ are the units in two different systems. If the dimensional formula of the quantity is [MᵃLᵇTᶜ], the conversion formula becomes n₂ = n₁ [M₁/M₂]ᵃ [L₁/L₂]ᵇ [T₁/T₂]ᶜ. For example, converting 1 Newton (SI) to dynes (CGS), we find that 1 N = 10⁵ dyne by substituting the respective base units.
10. Are dimensionless quantities always unitless? Explain with an example.
No, a dimensionless quantity is not necessarily unitless. A quantity is dimensionless if its dimensional formula is [M⁰L⁰T⁰]. While many such quantities like strain or refractive index are unitless, some possess units. A key example is angle. Plane angle, defined as the ratio of arc length to radius ([L]/[L]), is dimensionless but has the SI unit radian (rad). This is a crucial concept for solving advanced problems.
