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Class 9 · Advanced ScienceNCERT 2026 Revised Syllabus

Chapter 1: Measurement - The Foundation of Science

Science Advanced

Systems of units (CGS, FPS, SI), unit conversion, why measurement matters in physics and trade, and the relation Magnitude = Numerical value × Unit.

Find complete NCERT solutions for Class 9 Advanced Science, Science Advanced Chapter 1. Every question has a clear, step-by-step answer.

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Quick Check(4 questions)

1

Name any two systems of units.

Board Level Answers

Ans.
Solution:The CGS (centimetre-gram-second) system and the FPS (foot-pound-second) system are two commonly used systems of units.Answer: The CGS system and the FPS system.
2

Why is the SI system preferred over other systems?

Board Level Answers

Ans.
Solution:- The SI system is internationally accepted. - It is based on the decimal system. - It provides one uniform unit for each physical quantity, avoiding confusion.Answer: The SI system is internationally accepted, based on the decimal system, and provides one uniform unit for each physical quantity, avoiding confusion.
3
Hard

Convert 250 N into gcm/s2.

Board Level Answers

Ans.
Solution:$1 \text{ N} = 10^{5} \text{ g cm/s}^{2}$$250 \text{ N} = 250 \times 10^{5} = 2.5 \times 10^{7} \text{ g cm/s}^{2}$Answer: $250 \text{ N} = 2.5 \times 10^{7} \text{ g cm/s}^{2}$.
4
Hard

Convert 1000 kg/L into kg/m3.

Board Level Answers

Ans.
Solution:$1 \text{ L} = 10^{-3} \text{ m}^{3}$$1000 \text{ kg/L} = 1000 / 10^{-3} = 1 \times 10^{6} \text{ kg/m}^{3}$Answer: $1000 \text{ kg/L} = 1 \times 10^{6} \text{ kg/m}^{3}$.

Check Your Understanding(17 questions)

1

Which of the following is not an SI unit? (a) Meter (b) Kilogram (c) Second (d) Foot

Board Level Answers

Ans.
Solution:- SI base units include the metre, kilogram and second. - Foot belongs to the FPS system, not the SI system.Answer: (d) Foot is not an SI unit.
2

The SI unit of mass is: (a) Gram (b) Kilogram (c) Pound (d) Tonne

Board Level Answers

Ans.
Solution:- The SI base unit of mass is the kilogram. - Gram, pound and tonne are not SI base units of mass.Answer: (b) Kilogram is the SI unit of mass.
3

Name the system of units used internationally.

Board Level Answers

Ans.
Solution:The International System of Units (SI) is used internationally.Answer: The International System of Units (SI).
4

Why is a common system of units necessary?

Board Level Answers

Ans.
Solution:- Avoids confusion in trade. - Prevents errors in scientific calculations. - Allows scientific data to be shared and compared globally.Answer: A common system avoids confusion in trade, prevents errors in scientific calculations, and allows scientific data to be shared and compared globally.
5

Why is measurement necessary in physics?

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Ans.
Solution:- Physics is built entirely on measurable quantities. - Without accurate measurement of length, mass, and time, physical laws cannot be tested or applied.Answer: Physics is built entirely on measurable quantities; without accurate measurement of length, mass, and time, physical laws cannot be tested or applied.
6

Why was there a need for a common system of units?

Board Level Answers

Ans.
Solution:- Different regions used different units. - This caused confusion in trade, calculation errors, and difficulty comparing scientific data internationally.Answer: Different regions used different units, which caused confusion in trade, calculation errors, and difficulty comparing scientific data internationally.
7

Explain the relation: Magnitude = Numerical value × Unit.

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Ans.
Solution:- A physical quantity Q equals $n \times u$, where n is the numerical value and u is the unit chosen. - Q stays constant, but n changes when u changes.Answer: $Q = n \times u$; the physical quantity stays constant, but the numerical value changes when the unit changes.
8

Why does the same classroom floor give different numerical values when measured with sticks of different lengths?

Board Level Answers

Ans.
Solution:- The numerical value of a measurement is inversely proportional to the size of the unit used. - A longer stick (unit) gives a smaller numerical value.Answer: The numerical value of a measurement is inversely proportional to the size of the unit used, so a longer stick (unit) gives a smaller numerical value.
9

(Based on Activity 1.1) Why are numerical values different?

Board Level Answers

Ans.
Solution:- The numerical values differ because sticks of different lengths (different units) were used. - The same fixed floor dimensions were measured each time.Answer: The numerical values differ because sticks of different lengths (different units) were used to measure the same fixed floor dimensions.
10

Is the actual size of the classroom different? Why or why not?

Board Level Answers

Ans.
Solution:- No. The actual size of the classroom does not change. - Only the numerical value changes because a different sized unit was used each time.Answer: No. The actual size of the classroom does not change; only the numerical value changes because a different sized unit was used each time.
11

What conclusion can you draw about units and measurement from this activity?

Board Level Answers

Ans.
Solution:- The numerical value of a measured quantity depends entirely on the unit chosen. - The physical quantity itself remains fixed and unchanged.Answer: The numerical value of a measured quantity depends entirely on the unit chosen, while the physical quantity itself remains fixed and unchanged.
12

Fill in the blanks: (a) Measurement compares an unknown quantity with a ______ quantity. (b) SI unit of mass is ______. (c) In CGS, unit of length is ______. (d) 1 km = ______ m. (e) The modern internationally accepted system is called ______.

  1. a.(a) Measurement compares an unknown quantity with a ______ quantity.
  2. b.(b) SI unit of mass is ______.
  3. c.(c) In CGS, unit of length is ______.
  4. d.(d) 1 km = ______ m.
  5. e.(e) The modern internationally accepted system is called ______.

Board Level Answers

Ans.
Solution:(a) standard (b) kilogram (c) centimetre (d) 1000 (e) SI (International System of Units)Answer: (a) standard (b) kilogram (c) centimetre (d) 1000 (e) SI.
13

Match the following: Column A - CGS, FPS, SI, MKS; Column B - Kelvin, Pound, International system, Meter-Kilogram-Second.

Board Level Answers

Ans.
Solution:The printed options do not form a valid one-to-one match. Kelvin belongs to the SI system, and International system also denotes SI. The correct expansion of CGS is centimetre-gram-second, but that option is missing. FPS correctly corresponds to pound and MKS to metre-kilogram-second.Answer: The question is ambiguous/incomplete as printed; CGS has no correct matching option.
14

What problems might occur if every country used its own system of units for measurement?

Board Level Answers

Ans.
Solution:- Confusion in trade. - Communication errors. - Difficulty comparing scientific data. - Higher risk of calculation mistakes internationally.Answer: It would cause confusion in trade, communication errors, difficulty comparing scientific data, and a higher risk of calculation mistakes internationally.
15

A scientist measures length in feet and another in meters. What difficulties may this lead to?

Board Level Answers

Ans.
Solution:- Comparing or combining their results becomes difficult without conversion. - This increases the chance of errors and miscommunication in shared scientific work.Answer: Comparing or combining their results becomes difficult without conversion, increasing the chance of errors and miscommunication in shared scientific work.
16

If 1 meter was defined differently in different countries, what would happen to international trade?

Board Level Answers

Ans.
Solution:- Trade would suffer from inconsistent measurements. - Unfair transactions and disputes over quantity. - Difficulty verifying goods across borders.Answer: Trade would suffer from inconsistent measurements, unfair transactions, disputes over quantity, and difficulty verifying goods across borders.
17
Hard

A shopkeeper sells rice in kilograms. A foreign customer asks for rice in pounds. (a) Why is unit conversion necessary here? (b) If 1 kg = 2.2 pounds, how many pounds are in 5 kg?

  1. a.(a) Why is unit conversion necessary here?
  2. b.(b) If 1 kg = 2.2 pounds, how many pounds are in 5 kg?

Board Level Answers

Ans.
Solution:(a) Conversion is necessary because the two people use different unit systems, and conversion ensures both understand the same actual quantity.(b) $5 \times 2.2 = 11$ pounds.Answer: (a) Conversion is necessary because the two people use different unit systems. (b) 11 pounds.

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