20 short questions with answers Class 11 Physics Chapter on Units and Measurements:

Questions & Answers:

1.Question: What is a physical quantity?

Answer: A physical quantity is a quantity that can be measured and described by a numerical value and a unit.

2.Question: Name the fundamental SI units for length, mass, and time.

Answer: Meter (m), kilogram (kg), and second (s).

3.Question: What are derived units? Give one example.

Answer: Derived units are units obtained by combining fundamental units. Example: Velocity (m/s).

4.Question: Define a light-year.

Answer: A light-year is the distance that light travels in a vacuum in one year.

5.Question: What is the purpose of using significant figures in measurements? Answer: Significant figures indicate the precision of a measurement.

6.Question: State the rules for determining significant figures in a number.

Answer: (i) All non-zero digits are significant. (ii) Zeros between non-zero digits are significant. (iii) Leading zeros are not significant. (iv) Trailing zeros in a number with a decimal point are significant. (v) Trailing zeros in a number without a decimal point may or may not be significant.

7.Question: What is dimensional analysis?

Answer: Dimensional analysis is a technique used to check the consistency of equations by comparing the dimensions of the terms on both sides.

8.Question: What are the dimensions of force?

Answer: [MLT−2].

9.Question: Write the SI unit of pressure and its dimensional formula. Answer: Pascal (Pa), [ML−1T−2].

10.Question: What is meant by the precision of a measurement?

Answer: Precision refers to the closeness of various measurements for the same quantity.

11.Question: What is meant by the accuracy of a measurement?

Answer: Accuracy refers to how close a measurement is to the true value of the quantity.

12.Question: Give an example of a systematic error.

Answer: Zero error in a measuring instrument.

13.Question: What are random errors?

Answer: Random errors are unpredictable fluctuations in measurements due to chance variations.

14.Question: How can random errors be minimized?

Answer: By taking multiple measurements and calculating their arithmetic mean.

15.Question: What is the order of magnitude of the diameter of the Earth (≈1.27×107 m)?

Answer: 107 m.

16.Question: Convert 1 kilometer to micrometers.

: 109 micrometers.

17.Question: What is the SI prefix for 10−15?

Answer: femto (f).

18.Question: Name a device used to measure very small distances.

Answer: Screw gauge or Vernier caliper.

19.Question: What is the principle behind measuring large astronomical distances using the parallax method?

Answer: Measuring the apparent shift in the position of a distant object when viewed from two different points of observation.

20.Question: Can a quantity have units but no dimensions?

Answer: No, if a quantity has a unit, it must have corresponding dimensions. Dimensionless quantities have no units.