**Lesson 1**** Measurement**

**9th Science Guide:** Hello students, on this page, you can find the 9th Standard Science Solutions for the unit ‘Measurement.’ We have covered almost all the book back questions from the first unit of Class 9 Science, which is Measurement, as well as some additional questions that we expect to be included in the final exam.

## Measurement Book Back Answers

Below, you can find the answers for the following sections: “Choose the Correct Answer,” “Fill in the Blanks,” “State Whether True or False,” and so on.

**I. Choose the correct answer :**

1. Choose the correct one.

- mm < cm < m < km
- mm > cm > m > km
- km < m < cm < mm
- mm > m > cm > km

Ans: mm < cm < m < km

2. Rulers, measuring tapes, and meter scales are used to measure

- mass
- weight
- time
- length

Ans: length

3. 1 metric ton is equal to

- 100 quintals
- 10 quintals
- 1/10 quintals
- 1/100 quintals

Ans: 10 quintals

4. Which among the following is not a device to measure mass?

- Spring balance
- Beam balance
- Physical balance
- Digital balance

Ans: Spring balance

**II. Fill in the blanks :**

1. Metre is the unit of _______________.

Ans: length

2. 1 kg of rice is weighed by _______________.

Ans: beam balance

3. Thickness of a cricket ball is measured by _________.

Ans: vernier caliper

4. Radius of a thin wire is measured by ________.

Ans: screw gauge

5. A physical balance measures small differences in mass up to ___________.

Ans: 1mg or less

**III. State whether true or false. If false, correct the statement**

1. The SI unit of electric current is the kilogram. ( False )

Correct statement: The SI unit of electric current is ampere.

2. Kilometre is one of the SI units of measurement. ( True )

3. In everyday life, we use the term weight instead of mass. ( True )

4. A physical balance is more sensitive than a beam balance. ( True )

5. One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K. ( True )

6. With the help of an vernier caliper we can have an accuracy of 0.1 mm and with a screw gauge, we can have an accuracy of 0.01 mm. ( True )

**IV. Match the following**

Column I | Column II |

1. Length | Kelvin |

2. Mass | meter |

3. Time | kilogram |

4. Temperature | second |

Ans : 1 – B, 2 – C, 3 – D, 4 – A |

Column I | Column II |

1. Screw gauge | Vegetables |

2. Vernier caliper | Coins |

3. Beam balance | Gold ornaments |

4. Digital balance | Cricket ball |

Ans : 1 – B, 2 – D, 3 – A, 4 – C |

Column I | Column II |

1. Temperature | Beam balance |

2. Mass | Ruler |

3. Length | Digital clock |

4. Time | Thermometer |

Ans : 1 – D, 2 – A, 3 – B, 4 – C |

**V. Assertion and reason type**

1. **Assertion(A):** The scientifically correct expression is “ The mass of the bag is 10 kg”

** Reason (R)**: In everyday life, we use the term weight instead of mass.

- Both A and R are true but R is not the correct reason
- Both A and R are true and R is the correct reason
- A is true but R is false
- A is false but R is true

Ans: Both A and R are true but R is not the correct reason

2. **Assertion (A)**: 0 °C = 273.16 K. For our convenience we take it as 273 K after rounding off the decimal

** Reason (R**): To convert a temperature on the Celsius scale we have to add 273 to the given temperature.

- Both A and R are true but R is not the correct reason
- Both A and R are true and R is the correct reason
- A is true but R is false
- A is false but R is true

Ans: Both A and R are true and R is the correct reason

3. **Assertion (A)**: Distance between two celestial bodies is measured in terms of light year.

** Reason (R)**: The distance traveled by light in one year is one light year

- Both A and R are true but R is not the correct reason
- Both A and R are true and R is the correct reason
- A is true but R is false
- A is false but R is true

Ans: A is false but R is true

4. **Assertion (A)**: The SI systems of units are the improved system of units for measurement.

** Reason (R):** The SI unit of mass is a kilogram

- Both A and R are true but R is not the correct reason
- Both A and R are true and R is the correct reason
- A is true but R is false
- A is false but R is true

Ans: Both A and R are true and R is the correct reason

**VI. Comprehensive type**

**Read the passage and answer the questions given below.**

Mass is the amount of matter contained in an object. Measurement of mass helps us to distinguish between a lighter and a heavier body. Beam balance, spring balance, and electronic balance are used to measure the mass of different objects. The SI unit of mass is the kilogram (kg). But different units are used to measure the mass of different objects. E.g. weight (mass) of a tablet is measured in milligrams (mg), the weight of a student is measured in kilograms (kg), and the weight of a truck with goods is measured in metric tons. One metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

**1. The value of 1 metric ton is equal to**

- 1000 kg
- 10 quintals
- 10,00,000 g
- 100 kg

Ans: 1000 kg

**2. How will you measure the weight of a tablet?**

- kg
- g
- mg
- None of these

Ans: mg

**VII. Very short answer type**

**1. Define measurement.**

Measurement is the process of comparison of the given physical quantity with the know standard quantity of the same nature

**2. Define standard unit.**

SI System of units is the modernized and improved form of the previous system of units.

**3. What is the full form of the SI system?**

An international system of units.

**4. Define the least count of any device**

- The smallest length which can be measured by meter scale is called the least count.
- Least count of the instrument = Value of one main scale division / Total number of vernier scale division

Least count _ Pitch / No. of head scale divisions

**5. What do you know about the pitch of screw gauge?**

The pitch of the screw gauge is the distance between two successive screw threads. It is measured by the ratio of distance traveled on the pitch scale to the number of rotations of the head scale.

Pitch = Distance traveled on the pitch scale / Number of rotations of the head scale

**6. Can you find the diameter of a thin wire of length 2 m using the ruler from your instrument box?**

No, I can not find the diameter of a thin wire of length 2 m using the ruler.

**VIII. Short answer type**

**1. Write the rules that are followed in writing the symbols of units in the SI system.**

(i) Units named after scientists are written in lowercase.

- Eg. joule, Kelvin, and Newton.

(ii) Symbols for the units are always written in lowercase.

- Eg. m, kg, and s.

(iii) However, the symbols for the units derived from the names of scientists are written in capital letters.

- Eg. C (Celsius), N (Newton), and J (joule).

(iv) Symbols are not followed by a full stop.

- Eg. 75 cm and not 75 cm.

(v) Symbols are never written in the plural.

- Eg. 100 kg, not 100 kgs.

**2. Write the need for a standard unit**

A Standard Unit is needed to maintain uniformity in measurements like length, weight, size, and distance.

Eg: the Standard Unit of length is a meter.

**3. Differentiate mass and weight**

Mass | Weight |

1. Fundamental quantity | Derived quantity |

2. Has magnitude alone scalar quantity | Has magnitude and direction – vector quantity |

3. It is the amount of matter contained in a body | It is the normal force exerted by the surface on the object against the gravitational pull |

4, Remains the same | Varies from place to place |

5. Itis measured using physical balance | It is measured using a spring balance |

6. Its unit is the kilogram | Its unit is Newton |

**4. How will you measure the least count of the vernier caliper?**

The least Count or L.C. is the minimum reading or value that can be measured with a measuring tool or device.

**IX. Numerical Problems**

**1. Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 x 10/5 m and Ezhilan argues that it is 9.46 x 10. km. Who is right? Justify your answer.**

Solution: (Inian is correct)

Light travels 3 x 10^{8} m in one second or 3 Lakhs kilometer in one second.

In one year we have 365 days.

The total number of seconds in one year is equal to 365 | = 24 x 60 x 60 |

Distance traveled by light in 1 year | = 3.153 x 10^{7} x 3 x 10^{8} |

= 9,46 x 10^{15} m. |

**2. The main scale reading while measuring the thickness of a rubber ball using a Vernier caliper is 7 cm and the Vernier scale coincidence is 6. Find the radius of the ball.**

Solution:

MSR | = 7cm |

VC | = 6cm |

LC | = 0.1mm=0.1 cm |

Diameter | =DR = MSR+(VC xLC) |

= 7+0.06cm | |

Diameter D | = 7.06cm |

Radius R | = D/2 = 7.06/2 = 0.035 m |

The radius of the ball = 0.0353 m. |

**3. Find the thickness of a five rupee coin with the screw gauge, if the pitch scale reading is 1 mm and its head scale coincidence is 68.**

Solution:

PSR | = Imm =1 x 10^{-3} m |

HSC | = 68 |

LC | = 0.01 mm =0.01 x 10^{-3} m |

Total reading | = PSR+(HSC x LC) |

The thickness of the five-rupee coin | = 1 x 10^{-3} +(68 « 0.01 x 10^{-3}) m |

The thickness of the five-rupee coin | = 1.68 x 10^{-3} m= 1.68 mm |

**4. Find the mass of an object weighing 98 N.**

Solution:

W | = mg |

W | = 9N |

g | = 98 m/s2 |

m | W/g = 98 / 9.8 =10 Kg. |

**IX. Long Answer Type**

**1. Explain a method to find the thickness of a hollow tea cup.**

**Step-1:** The Pitch, Least count and the type of zero error of the screw gauge are determined.

**Step-2:** The given cup is placed in between two studs.

**Step-3:** The head screw using the ratchet arrangement is freely rotated until the given cup is held firmly, but not tightly.

**Step-4:** Pitch scale reading (PSR) by the head scale and head scale coincidence (HSC) with the axis of the pitch scale, are found.

**Step-5:** The readings are recorded and the experiment for different positions of the given cup is repeated.

**Step-6:** The thickness of the cup is calculated using the formula P.’S.R+(HSCxL.C )

**Step-7:** Then the average of the last column of the table. is found.

Main Scale Reading MSR x 10^{-4} m | Vernier Scale Coincidence | Observed Reading OR = MSR + (LC X VC) | Corrected Reading = OR + ZC |

1. | |||

2. | |||

3. | |||

4. |

Hence the thickness of a hollow tea cup = _______________ mm.

**2. How will you find the thickness of a one-rupee coin?**

**Step-1:** The Pitch, Least count and the type of zero error of the screw gauge are determined.

**Step-2:** The given coin is placed in between two studs.

**Step-3:** The head screw using the ratchet arrangement is freely rotated until given one rupee coin is held firmly, but not tightly.

**Step-4:** Pitch scale reading (PSR) by the head scale and head scale coincidence (HSC) with the axis of the pitch scale are found.

**Step-5:** The reading is recorded and the experiment for different positions of the given coin is repeated.

**Step-6:** The thickness of the coin is computed using the formula P.’S.R+(HSCxL.C )

**Step-7:** Then the average of the last column of the table is found.

P.S.R. (mm) | HSC (division) | CHSC = HSC + ZC (Division) | CHSR = CHSC x LC (mm) | Total Reading = PSR + CHSR (mm) |

1. | ||||

2. | ||||

3. |

Mean = ___________ mm

Hence the thickness of a one rupee coin = ________ mm

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**Last Updated: 29th June 2023**