**1. What are units of measurement?**

**Answer:** Units of measurement are standard quantities used to specify measurements. They provide a reference for measuring physical quantities.

**2. What is a system of units?**

**Answer:** A system of units is a complete set of units used for all physical quantities. Examples include the International System of Units (SI), the British Imperial system, and the US customary system.

**3. What are SI Units?**

**Answer:** SI Units (International System of Units) are the standard units of measurement used globally in science and industry. They include seven base units: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).

**4. Define fundamental units.**

**Answer:** Fundamental units are the basic units of measurement for physical quantities from which other units are derived. In the SI system, the fundamental units are meter, kilogram, second, ampere, kelvin, mole, and candela.

**5. What are derived units?**

**Answer:** Derived units are units of measurement that are combinations of the fundamental units. Examples include velocity (meters per second, m/s), force (newton, N), and pressure (pascal, Pa).

**6. What is least count?**

**Answer:** The least count is the smallest measurement that can be accurately read on a measuring instrument. It defines the precision of the instrument.

**7. Explain significant figures.**

**Answer:** Significant figures are the digits in a measurement that are known with certainty plus the first uncertain digit. They reflect the precision of a measurement.

**8. What are errors in measurements?**

**Answer:** Errors in measurements are the deviations of the measured value from the true value. They can be systematic (consistent and repeatable) or random (varying and unpredictable).

**9. Define systematic errors.**

**Answer:** Systematic errors are consistent, repeatable errors associated with faulty equipment or experimental design. These errors affect the accuracy of measurements.

**10. Define random errors.**

**Answer:** Random errors are unpredictable variations that occur during measurement. They affect the precision of measurements and are caused by uncontrollable factors.

**11. What are dimensions of physical quantities?**

**Answer:** Dimensions of physical quantities are the powers to which the base units are raised to represent a quantity. For example, the dimension of velocity is [L][T]⁻¹, where L represents length and T represents time.

**12. Explain dimensional analysis.**

**Answer:** Dimensional analysis is a method used to check the consistency of equations and to derive relations among physical quantities by analyzing their dimensions.

**13. How is dimensional analysis useful?**

**Answer:** Dimensional analysis is useful for verifying the correctness of equations, converting units, and deriving relationships between physical quantities.

**14. What is a dimensionless quantity?**

**Answer:** A dimensionless quantity is a quantity without any physical units and dimensions. Examples include pure numbers, angles (radians), and ratios.

**15. Give an example of a fundamental quantity and its unit.**

**Answer:** Length is a fundamental quantity, and its unit in the SI system is the meter (m).

**16. Give an example of a derived quantity and its unit.**

**Answer:** Speed is a derived quantity, and its unit in the SI system is meters per second (m/s).

**17. What is the principle of homogeneity of dimensions?**

**Answer:** The principle of homogeneity of dimensions states that all terms in a physical equation must have the same dimensions. This ensures the equation is dimensionally consistent.

**18. Why are significant figures important in measurements?**

**Answer:** Significant figures are important because they indicate the precision of a measurement and the uncertainty in the last digit.

**19. What is the base unit for temperature in the SI system?**

**Answer:** The base unit for temperature in the SI system is the kelvin (K).

**20. What is the dimension of force?**

**Answer:** The dimension of force is [M][L][T]⁻², where M represents mass, L represents length, and T represents time.