##### Class 9^{th} Science Tamilnadu Board Solution

**Multiple Choice Questions**- Choose the correct one
- Rulers, measuring tapes and metre scales are used to measure
- 1 metric ton is equal to
- Distance between Chennai and Kanyakumari can be found in
- Which among the following is not a device to measure mass?

**Long Answer Type**- Explain a method to find the thickness of a hollow tea cup.
- How will you find the thickness of a one rupee coin?
- Find out any ‘ten words’ related to measurement from the

**Activity****Fill In The Blanks**- Metre is the unit of ________
- 1 kg of rice is weighed by ______
- The thickness of a cricket ball is measured by _______
- The radius of a thin wire is measured by ________
- A physical balance measures small differences in mass up to ______…

**True Or False**- The SI unit of electric current is kilogram
- Kilometre is one of the SI units of measurement
- In everyday life, we use the term weight instead of mass.
- A physical balance is more sensitive than a beam balance as it can accurately measure even…
- One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K.…

**Match The Following**- Column IColumn IILengthKelvinMassmetreTimekilogramTemperaturesecond…
- Column IColumn IIScrew gaugeVegetablesVernier caliperCoinsBeam balanceGold…
- Column IColumn IITemperatureBeam balanceMassRulerLengthDigital clockTimeThermometer…

**Assertion And Reason Type**- Assertion (A): The SI system of units is the improved system of units for…
- Assertion (A): The skill of estimation is important for all of us in our daily life.Reason…
- Assertion(A): The scientifically correct expression is “ The mass of the bag is 10…
- Assertion (A): 0 °C = 273.16 K. For our convenience we take it as 273 K after rounding off…
- Assertion (A): The distance between two celestial bodies is measured in the unit of light…

**Comprehensive Type**- Read the passage and answer the questions given below.Mass is the amount of matter…
- Read the passage and answer the questions given below.Mass is the amount of matter…

**Very Short Answer Type**- Define measurement.
- Define standard unit.
- What is the full form of SI system?
- Define least count of any device.
- What do you know about pitch of screw gauge?
- Can you find the diameter of a thin wire of length 2 m using the ruler from your…

**Short Answer Type**- Write the rules that are followed in writing the symbols of units in SI system.…
- Write the need of a standard unit
- Differentiate mass and weight
- What is the measuring unit of the thickness of a plastic carry bag?…
- How will you measure the least count of vernier caliper?

**Numerical Problem**- Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 × 1015 m and…
- The main scale reading while measuring the thickness of a rubber ball using Vernier…
- Find the thickness of a five rupee coin with the screw gauge, if the pitch scale reading…
- Find the mass of an object weighing 98 N.

**Multiple Choice Questions**

- Choose the correct one
- Rulers, measuring tapes and metre scales are used to measure
- 1 metric ton is equal to
- Distance between Chennai and Kanyakumari can be found in
- Which among the following is not a device to measure mass?

**Long Answer Type**

- Explain a method to find the thickness of a hollow tea cup.
- How will you find the thickness of a one rupee coin?
- Find out any ‘ten words’ related to measurement from the

**Activity**

**Fill In The Blanks**

- Metre is the unit of ________
- 1 kg of rice is weighed by ______
- The thickness of a cricket ball is measured by _______
- The radius of a thin wire is measured by ________
- A physical balance measures small differences in mass up to ______…

**True Or False**

- The SI unit of electric current is kilogram
- Kilometre is one of the SI units of measurement
- In everyday life, we use the term weight instead of mass.
- A physical balance is more sensitive than a beam balance as it can accurately measure even…
- One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K.…

**Match The Following**

- Column IColumn IILengthKelvinMassmetreTimekilogramTemperaturesecond…
- Column IColumn IIScrew gaugeVegetablesVernier caliperCoinsBeam balanceGold…
- Column IColumn IITemperatureBeam balanceMassRulerLengthDigital clockTimeThermometer…

**Assertion And Reason Type**

- Assertion (A): The SI system of units is the improved system of units for…
- Assertion (A): The skill of estimation is important for all of us in our daily life.Reason…
- Assertion(A): The scientifically correct expression is “ The mass of the bag is 10…
- Assertion (A): 0 °C = 273.16 K. For our convenience we take it as 273 K after rounding off…
- Assertion (A): The distance between two celestial bodies is measured in the unit of light…

**Comprehensive Type**

- Read the passage and answer the questions given below.Mass is the amount of matter…
- Read the passage and answer the questions given below.Mass is the amount of matter…

**Very Short Answer Type**

- Define measurement.
- Define standard unit.
- What is the full form of SI system?
- Define least count of any device.
- What do you know about pitch of screw gauge?
- Can you find the diameter of a thin wire of length 2 m using the ruler from your…

**Short Answer Type**

- Write the rules that are followed in writing the symbols of units in SI system.…
- Write the need of a standard unit
- Differentiate mass and weight
- What is the measuring unit of the thickness of a plastic carry bag?…
- How will you measure the least count of vernier caliper?

**Numerical Problem**

- Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 × 1015 m and…
- The main scale reading while measuring the thickness of a rubber ball using Vernier…
- Find the thickness of a five rupee coin with the screw gauge, if the pitch scale reading…
- Find the mass of an object weighing 98 N.

###### Multiple Choice Questions

**Question 1.**Choose the correct one

A. mm< cm < m < km

B. mm > cm > m > km

C. km < m < cm < mm

D. mm > m> cm> km

**Answer:**We know that 1km = 10^{3} m = 10^{5} cm = 10^{6} mm

So, mm < cm < m < km.

**Question 2.**Rulers, measuring tapes and metre scales are used to measure

A. Mass

B. Weight

C. Time

D. Length

**Answer:**Metre is a unit of length and rulers, metre scales and measuring tapes are used to measure length.

**Question 3.**1 metric ton is equal to

A. 100 quintals

B. 10 quintals

C. 1/10 quintals

D. 1/100 quintals

**Answer:**1 metric ton = 1000 kg and 1 quintal = 100 kg

So, 1 metric ton = 10 quintals.

**Question 4.**Distance between Chennai and Kanyakumari can be found in

A. Kilometres

B. Metres

C. Centimetres

D. Millimetres

**Answer:**Chennai and Kanyakumari are two cities and distance between them is large. So, it is measured in kilometres.

**Question 5.**Which among the following is not a device to measure mass?

A. Spring balance

B. Beam balance

C. Physical balance

D. Digital balance

**Answer:**Spring balance is used to measure weight not mass.

**Question 1.**

Choose the correct one

A. mm< cm < m < km

B. mm > cm > m > km

C. km < m < cm < mm

D. mm > m> cm> km

**Answer:**

We know that 1km = 10^{3} m = 10^{5} cm = 10^{6} mm

So, mm < cm < m < km.

**Question 2.**

Rulers, measuring tapes and metre scales are used to measure

A. Mass

B. Weight

C. Time

D. Length

**Answer:**

Metre is a unit of length and rulers, metre scales and measuring tapes are used to measure length.

**Question 3.**

1 metric ton is equal to

A. 100 quintals

B. 10 quintals

C. 1/10 quintals

D. 1/100 quintals

**Answer:**

1 metric ton = 1000 kg and 1 quintal = 100 kg

So, 1 metric ton = 10 quintals.

**Question 4.**

Distance between Chennai and Kanyakumari can be found in

A. Kilometres

B. Metres

C. Centimetres

D. Millimetres

**Answer:**

Chennai and Kanyakumari are two cities and distance between them is large. So, it is measured in kilometres.

**Question 5.**

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

A. Spring balance

B. Beam balance

C. Physical balance

D. Digital balance

**Answer:**

Spring balance is used to measure weight not mass.

###### Long Answer Type

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

**Answer:**We can find the thickness of a hollow tea cup by using screw gauge. To find the thickness of the cup, follow given steps:

i) Determine the least count, pitch and the zero error of the screw gauge.

ii) Hold the cup between anvil and spindle.

iii) Rotate the head until the cup is held firmly but not tightly, with the help of the ratchat .

iv) ) Note the reading of the pitch scale crossed by the head scale (PSR) and the head scale division that coincides with the pitch scale axis (HSC).

v) The thickness of the cup is given by PSR + CHSR (Corrected HSR). Repeat the experiment for different positions of the coin.

vi) Note the readings in a table.

vii) The average of the last column readings gives the thickness of the cup.

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

**Answer:**We can find the thickness of a one rupee coin by using a screw gauge. It can be done in following steps:

i) Determine the pitch, the least count and the zero error of the screw gauge.

ii) Place the coin between the two studs.

iii) Rotate the head until the coin is held firmly but not tightly, with the help of the ratchat .

iv) Note the reading of the pitch scale crossed by the head scale (PSR) and the head scale division that coincides with the pitch scale axis (HSC).

v) The width of the coin is given by PSR + CHSR (Corrected HSR). Repeat the experiment for different positions of the coin.

vi) Tabulate the readings.

vii) The average of the last column readings gives the thickness of the coin.

**Question 3.**Find out any ‘ten words’ related to measurement from the grid.

**Answer:**i) ACCURATE

ii) VERNIER

iii) KELVIN

iv) NEWTON

v) LEAST COUNT

vi) PITCH

vii) ERROR

viii) BEAM

ix) SCREW

x) CONSTANT

**Question 1.**

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

**Answer:**

We can find the thickness of a hollow tea cup by using screw gauge. To find the thickness of the cup, follow given steps:

i) Determine the least count, pitch and the zero error of the screw gauge.

ii) Hold the cup between anvil and spindle.

iii) Rotate the head until the cup is held firmly but not tightly, with the help of the ratchat .

iv) ) Note the reading of the pitch scale crossed by the head scale (PSR) and the head scale division that coincides with the pitch scale axis (HSC).

v) The thickness of the cup is given by PSR + CHSR (Corrected HSR). Repeat the experiment for different positions of the coin.

vi) Note the readings in a table.

vii) The average of the last column readings gives the thickness of the cup.

**Question 2.**

How will you find the thickness of a one rupee coin?

**Answer:**

We can find the thickness of a one rupee coin by using a screw gauge. It can be done in following steps:

i) Determine the pitch, the least count and the zero error of the screw gauge.

ii) Place the coin between the two studs.

iii) Rotate the head until the coin is held firmly but not tightly, with the help of the ratchat .

iv) Note the reading of the pitch scale crossed by the head scale (PSR) and the head scale division that coincides with the pitch scale axis (HSC).

v) The width of the coin is given by PSR + CHSR (Corrected HSR). Repeat the experiment for different positions of the coin.

vi) Tabulate the readings.

vii) The average of the last column readings gives the thickness of the coin.

**Question 3.**

Find out any ‘ten words’ related to measurement from the grid.

**Answer:**

i) ACCURATE

ii) VERNIER

iii) KELVIN

iv) NEWTON

v) LEAST COUNT

vi) PITCH

vii) ERROR

viii) BEAM

ix) SCREW

x) CONSTANT

###### Activity

**Question 1.**Complete the flow chart

**Answer:**

Unit of mass is kg and unit of volume is m^{3}. So Unit of Density is **kgm**^{-3}.

Unit of distance is m and unit of time is s. So unit of velocity is **ms**^{-1}.

Change in velocity has unit ms^{-1} and time has unit s. So unit of acceleration is **ms**^{-2}.

Unit of mass is kg and unit of acceleration is ms^{-2}. So Unit of Force in fundamental quantities is **kgms**^{-2}.

Unit of force is kgms^{-2} and unit of area is m^{2}. So unit of pressure is **kgm**^{-1}s^{-2}.

**Question 1.**

Complete the flow chart

**Answer:**

Unit of mass is kg and unit of volume is m^{3}. So Unit of Density is **kgm ^{-3}**.

Unit of distance is m and unit of time is s. So unit of velocity is **ms ^{-1}**.

Change in velocity has unit ms^{-1} and time has unit s. So unit of acceleration is **ms ^{-2}**.

Unit of mass is kg and unit of acceleration is ms^{-2}. So Unit of Force in fundamental quantities is **kgms ^{-2}**.

Unit of force is kgms^{-2} and unit of area is m^{2}. So unit of pressure is **kgm ^{-1}s^{-2}**.

###### Fill In The Blanks

**Question 1.**Metre is the unit of ________

**Answer:**Metre is the unit of __length__.

**Explanation:** Metre is the SI unit of Length.

**Question 2.**1 kg of rice is weighed by ______

**Answer:**1 kg of rice is weighed by __beam balance__.

**Explanation:**

A beam balance compares the sample mass with a standard reference mass. Standard reference masses are 5g, 10g, 20g, 50g, 100g, 200g, 500g, 1kg, 2kg, 5kg. So it is used to measure 1 kg of rice.

**Question 3.**The thickness of a cricket ball is measured by _______

**Answer:**The thickness of a cricket ball is measured by __vernier scale__.

**Explanation:**

The diameters of spherical objects such as cricket ball and hollow objects such as a pen cap cannot be measured with a meter scale. For this purpose, we use vernier scale to measure inner and outer diameter.

**Question 4.**The radius of a thin wire is measured by ________

**Answer:**The radius of a thin wire is measured by __screw gauge__.

**Explanation:** Radius of a thin wire is very small to measure. It can’t be measured by metre scale or vernier scale. But screw gauge can measure upto 0.01 mm. So, it is used for measuring radius of a thin wire.

**Question 5.**A physical balance measures small differences in mass up to ______

**Answer:**A physical balance measures small differences in mass up to __milligram__.

**Explanation:** Physical balance is very sensitive and used in labs for measuring. It is similar to beam balance. It can measure correctly up to milligram.

**Question 1.**

Metre is the unit of ________

**Answer:**

Metre is the unit of __length__.

**Explanation:** Metre is the SI unit of Length.

**Question 2.**

1 kg of rice is weighed by ______

**Answer:**

1 kg of rice is weighed by __beam balance__.

**Explanation:**

A beam balance compares the sample mass with a standard reference mass. Standard reference masses are 5g, 10g, 20g, 50g, 100g, 200g, 500g, 1kg, 2kg, 5kg. So it is used to measure 1 kg of rice.

**Question 3.**

The thickness of a cricket ball is measured by _______

**Answer:**

The thickness of a cricket ball is measured by __vernier scale__.

**Explanation:**

The diameters of spherical objects such as cricket ball and hollow objects such as a pen cap cannot be measured with a meter scale. For this purpose, we use vernier scale to measure inner and outer diameter.

**Question 4.**

The radius of a thin wire is measured by ________

**Answer:**

The radius of a thin wire is measured by __screw gauge__.

**Explanation:** Radius of a thin wire is very small to measure. It can’t be measured by metre scale or vernier scale. But screw gauge can measure upto 0.01 mm. So, it is used for measuring radius of a thin wire.

**Question 5.**

A physical balance measures small differences in mass up to ______

**Answer:**

A physical balance measures small differences in mass up to __milligram__.

**Explanation:** Physical balance is very sensitive and used in labs for measuring. It is similar to beam balance. It can measure correctly up to milligram.

###### True Or False

**Question 1.**The SI unit of electric current is kilogram

**Answer:**False

**Explanation:** Kilogram is unit of mass and electric current is measured in ampere.

**Question 2.**Kilometre is one of the SI units of measurement

**Answer:**True

**Explanation:** Kilogram is SI unit of mass.

**Question 3.**In everyday life, we use the term weight instead of mass.

**Answer:**True

**Explanation:** In day-to-day life, we generally ask for the weight of a substance.

**Question 4.**A physical balance is more sensitive than a beam balance as it can accurately measure even a very small mass, even milligram

**Answer:**True

**Explanation:** Physical balance is very sensitive and used in labs for measuring. It is similar to beam balance. It can measure small differences in mass up to milligram.

**Question 5.**One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K.

**Answer:**True

**Explanation:** Zero degree Celsius is equal to 273.15 K and 1 degree Celsius is equal to interval of 1 K.

1 degree Celsius = 273.15 K + 1 K = 274.15 K

**Question 1.**

The SI unit of electric current is kilogram

**Answer:**

False

**Explanation:** Kilogram is unit of mass and electric current is measured in ampere.

**Question 2.**

Kilometre is one of the SI units of measurement

**Answer:**

True

**Explanation:** Kilogram is SI unit of mass.

**Question 3.**

In everyday life, we use the term weight instead of mass.

**Answer:**

True

**Explanation:** In day-to-day life, we generally ask for the weight of a substance.

**Question 4.**

A physical balance is more sensitive than a beam balance as it can accurately measure even a very small mass, even milligram

**Answer:**

True

**Explanation:** Physical balance is very sensitive and used in labs for measuring. It is similar to beam balance. It can measure small differences in mass up to milligram.

**Question 5.**

One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K.

**Answer:**

True

**Explanation:** Zero degree Celsius is equal to 273.15 K and 1 degree Celsius is equal to interval of 1 K.

1 degree Celsius = 273.15 K + 1 K = 274.15 K

###### Match The Following

**Question 1.**

**Answer:**Hint: Based on SI unit of measurement.

SI unit of length is metre.

SI unit of mass is kilogram.

SI unit of time is second.

SI unit of temperature is Kelvin.

**Question 2.**

**Answer:**Hint: Based on things measured by devices.

Thickness of coins can be measured by using screw gauge.

Diameter of cricket ball can be measured by using vernier caliper.

Mass of vegetables can be measured by using beam balance.

Mass of Gold can be measured by using Digital balance.

**Question 3.**

**Answer:**Hint: Based on measuring devices and physical quantities.

Temperature can be measured by using Thermometer.

Mass can be measured by using Beam Balance.

Length can be measured by using Ruler.

Time can be measured by using Digital clock.

**Question 1.**

**Answer:**

Hint: Based on SI unit of measurement.

SI unit of length is metre.

SI unit of mass is kilogram.

SI unit of time is second.

SI unit of temperature is Kelvin.

**Question 2.**

**Answer:**

Hint: Based on things measured by devices.

Thickness of coins can be measured by using screw gauge.

Diameter of cricket ball can be measured by using vernier caliper.

Mass of vegetables can be measured by using beam balance.

Mass of Gold can be measured by using Digital balance.

**Question 3.**

**Answer:**

Hint: Based on measuring devices and physical quantities.

Temperature can be measured by using Thermometer.

Mass can be measured by using Beam Balance.

Length can be measured by using Ruler.

Time can be measured by using Digital clock.

###### Assertion And Reason Type

**Question 1.**Assertion (A): The SI system of units is the improved system of units for measurement.

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

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**Here, R is not giving proper reason that how SI system of units is the improved system of units of measurement. SI unit system is improved system as it has fixed reference and accepted in all over the world.

**Question 2.**Assertion (A): The skill of estimation is important for all of us in our daily life.

Reason (R): The skill of estimation reduces our consumption of time

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**Estimating a value makes calculation easy.

When we’re purchasing tickets for a group of people or splitting

the cost of dinner between 8 friends, we estimate for ease and to

save our time from more complex calculation.

**Question 3.**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

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**Reason behind assertion is “Kilogram is SI unit of mass”. So, for correct scientific expression, mass of the bag is 10 kg.

**Question 4.**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 you have to add 273 to the given temperature

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**We add 273 to temperature in Celsius to convert it into the Kelvin scale. Therefore, 0 ^{ο} c = 0+273 K = 273 K.

**Question 5.**Assertion (A): The distance between two celestial bodies is measured in the unit of light year

Reason (R): The distance travelled by the light in one year is one light year

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**The distance between two celestial bodies is measured in the unit of light year because these bodies are very far from each other and light year is larger unit for measuring length.

**Question 1.**

Assertion (A): The SI system of units is the improved system of units for measurement.

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

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**

Here, R is not giving proper reason that how SI system of units is the improved system of units of measurement. SI unit system is improved system as it has fixed reference and accepted in all over the world.

**Question 2.**

Assertion (A): The skill of estimation is important for all of us in our daily life.

Reason (R): The skill of estimation reduces our consumption of time

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**

Estimating a value makes calculation easy.

When we’re purchasing tickets for a group of people or splitting

the cost of dinner between 8 friends, we estimate for ease and to

save our time from more complex calculation.

**Question 3.**

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

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**

Reason behind assertion is “Kilogram is SI unit of mass”. So, for correct scientific expression, mass of the bag is 10 kg.

**Question 4.**

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 you have to add 273 to the given temperature

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**

We add 273 to temperature in Celsius to convert it into the Kelvin scale. Therefore, 0 ^{ο} c = 0+273 K = 273 K.

**Question 5.**

Assertion (A): The distance between two celestial bodies is measured in the unit of light year

Reason (R): The distance travelled by the light in one year is one light year

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

B. Both A and R are true and R is the correct reason

C. A is true but R is false

D. A is false but R is true

**Answer:**

The distance between two celestial bodies is measured in the unit of light year because these bodies are very far from each other and light year is larger unit for measuring length.

###### Comprehensive Type

**Question 1.**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 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), weight of a student is measured in kilogram (kg) and weight of a truck with goods is measured in metric tons. 1 metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

The value of 1 metric ton is equal to

A. 1000 kg

B. 10 quintals

C. 10,00,000 g

D. 100 kg

**Answer:**1 metric ton = 10 quintals and 1 quintal = 100 kg

Therefore, 1 metric ton = 10 × 100 = 1000 kg

**Question 2.**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 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), weight of a student is measured in kilogram (kg) and weight of a truck with goods is measured in metric tons. 1 metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

How will you measure the weight of a tablet?

A. kg

B. g

C. mg

D. None of these

**Answer:**Weight of a tablet is very less. So, it is measured in milligrams (mg).

**Question 1.**

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 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), weight of a student is measured in kilogram (kg) and weight of a truck with goods is measured in metric tons. 1 metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

The value of 1 metric ton is equal to

A. 1000 kg

B. 10 quintals

C. 10,00,000 g

D. 100 kg

**Answer:**

1 metric ton = 10 quintals and 1 quintal = 100 kg

Therefore, 1 metric ton = 10 × 100 = 1000 kg

**Question 2.**

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 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), weight of a student is measured in kilogram (kg) and weight of a truck with goods is measured in metric tons. 1 metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

How will you measure the weight of a tablet?

A. kg

B. g

C. mg

D. None of these

**Answer:**

Weight of a tablet is very less. So, it is measured in milligrams (mg).

###### Very Short Answer Type

**Question 1.**Define measurement.

**Answer:**Measurement is the assignment of a number to a characteristic of an object or event which can be compared with other objects or events. It is determination of the size or magnitude of something.

**Question 2.**Define standard unit.

**Answer:**A standard unit is a reference point by which objects of weight, length, or capacity can be described. Reference point will be fixed everywhere and will not change from person to person or place to place.

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

**Answer:**Full form of SI system is International System of Units.

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

**Answer:**The smallest value that can be measured by the measuring device is called its least count.

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

**Answer:**Pitch of screw gauge is equal to the distance travelled by the tip of the screw for one complete rotation of the head.

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

**Answer:**Yes. But it will not be much accurate as least count of my ruler is 1 mm.

**Question 1.**

Define measurement.

**Answer:**

Measurement is the assignment of a number to a characteristic of an object or event which can be compared with other objects or events. It is determination of the size or magnitude of something.

**Question 2.**

Define standard unit.

**Answer:**

A standard unit is a reference point by which objects of weight, length, or capacity can be described. Reference point will be fixed everywhere and will not change from person to person or place to place.

**Question 3.**

What is the full form of SI system?

**Answer:**

Full form of SI system is International System of Units.

**Question 4.**

Define least count of any device.

**Answer:**

The smallest value that can be measured by the measuring device is called its least count.

**Question 5.**

What do you know about pitch of screw gauge?

**Answer:**

Pitch of screw gauge is equal to the distance travelled by the tip of the screw for one complete rotation of the head.

**Question 6.**

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

**Answer:**

Yes. But it will not be much accurate as least count of my ruler is 1 mm.

###### Short Answer Type

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

**Answer:**Rules that are followed in writing the symbols of units in SI system are:

i) The symbols of the units named after scientists should be written by the initial capital letter. E.g. N for newton, H for henry, A for ampere and W for watt.

ii) Small letters are used as symbols for units not derived from a proper noun. E.g. m for metre, kg for kilogram.

iii) No full stop or other punctuation marks should be used within or at the end of symbols. E.g. 50 m and not as 50 m.

iv) The symbols of the units are not expressed in plural form. E.g. 10 kg not as kgs.

v) Use of solidus is recommended for indicating a division of one unit symbol by another unit symbol. Not more than one solidus is used. E.g. ms^{-1} or m/s. J/K/mol should be JK^{-1} mol^{-1}

vi) Accepted symbols alone should be used. E.g. ampere should not be written as amp and second should not be written as sec.

**Question 2.**Write the need of a standard unit

**Answer:**Standard unit is needed due to following reasons:

i) We needed to have fixed reference for measurement so that it doesn’t change from person to person.

ii) People in the different parts of the world were using different units which make the exchange of things difficult due to different units.

iii) We need units that will be accepted worldwide for ease of exchange and communication.

**Question 3.**Differentiate mass and weight

**Answer:**

**Question 4.**What is the measuring unit of the thickness of a plastic carry bag?

**Answer:**Thickness of a plastic carry bag can be measured in micrometre because plastic bags are very thin and can be measured by using screw gauge.

**Question 5.**How will you measure the least count of vernier caliper?

**Answer:**Least count of vernier caliper can be measured by following steps:

i) Find main scale division. The main scale division can easily

be obtained by inspecting the main scale. It will be in centimetre, further divided into millimetre. The value of smallest main scale division is 1 mm.

ii) Then find the vernier scale division. The Vernier scale division is obtained by counting number of division in it. In the Vernier scale there will be 10 divisions.

iii) To obtain least count, divide the smallest main scale division by total number of vernier scale division.

**Question 1.**

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

**Answer:**

Rules that are followed in writing the symbols of units in SI system are:

i) The symbols of the units named after scientists should be written by the initial capital letter. E.g. N for newton, H for henry, A for ampere and W for watt.

ii) Small letters are used as symbols for units not derived from a proper noun. E.g. m for metre, kg for kilogram.

iii) No full stop or other punctuation marks should be used within or at the end of symbols. E.g. 50 m and not as 50 m.

iv) The symbols of the units are not expressed in plural form. E.g. 10 kg not as kgs.

v) Use of solidus is recommended for indicating a division of one unit symbol by another unit symbol. Not more than one solidus is used. E.g. ms^{-1} or m/s. J/K/mol should be JK^{-1} mol^{-1}

vi) Accepted symbols alone should be used. E.g. ampere should not be written as amp and second should not be written as sec.

**Question 2.**

Write the need of a standard unit

**Answer:**

Standard unit is needed due to following reasons:

i) We needed to have fixed reference for measurement so that it doesn’t change from person to person.

ii) People in the different parts of the world were using different units which make the exchange of things difficult due to different units.

iii) We need units that will be accepted worldwide for ease of exchange and communication.

**Question 3.**

Differentiate mass and weight

**Answer:**

**Question 4.**

What is the measuring unit of the thickness of a plastic carry bag?

**Answer:**

Thickness of a plastic carry bag can be measured in micrometre because plastic bags are very thin and can be measured by using screw gauge.

**Question 5.**

How will you measure the least count of vernier caliper?

**Answer:**

Least count of vernier caliper can be measured by following steps:

i) Find main scale division. The main scale division can easily

be obtained by inspecting the main scale. It will be in centimetre, further divided into millimetre. The value of smallest main scale division is 1 mm.

ii) Then find the vernier scale division. The Vernier scale division is obtained by counting number of division in it. In the Vernier scale there will be 10 divisions.

iii) To obtain least count, divide the smallest main scale division by total number of vernier scale division.

###### Numerical Problem

**Question 1.**Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 × 10^{15} m and Ezhilan argues that it is 9.46 × 10^{12} km. Who is right? Justify your answer.

**Answer:**Speed of Light = 3 × 10^{8} ms^{-1}

Seconds in 1 year = 365 × 24 × 60 × 60

= 3.153 × 10^{7} seconds

Total distance in 1 light year = speed × time

= 3 × 10^{8} × 3.153 × 10^{7}

= 9.46 × 10^{15} m

1 m = 10^{-3} km

9.46 × 10^{15} m = 9.46 × 10^{12} km

Therefore, Inian and Ezhilan both are right.

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

**Answer:**Here, thickness of the rubber ball = diameter of the ball.

Main scale reading = 7 cm

Vernier scale reading = 6

Least count = 0.01 cm

Assuming, there is no zero error

Diameter of the ball =

Main scale reading (MSR) +

(Vernier scale coincidence (VC) × least count (LC)) ± ZE

= 7 + (6 × 0.01) ± 0

= 7.06 cm

Radius of ball

= 3.53 cm

Hence, radius of the ball is 3.53 cm.

**Question 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.

**Answer:**Given, Pitch scale reading (PSR) = 1 mm

Head scale coincidence (HSC) = 68

Least count (LC) = 0.01 mm

Assuming no zero error, we get

Corrected Head scale coincidence (CHSC) = 68

Thickness of the coin = PSR + (CHSC × LC)

**=** 1 + (68 × 0.01) mm

= 1.68 mm

Hence, Thickness of the coin is 1.68 mm.

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

**Answer:**weight = mass × gravity

We know that, gravity = 9.8 ms^{-2}

Given, weight = 98 N

= 10 kg

Hence, mass of the object is 10 kg.

**Question 1.**

Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 × 10^{15} m and Ezhilan argues that it is 9.46 × 10^{12} km. Who is right? Justify your answer.

**Answer:**

Speed of Light = 3 × 10^{8} ms^{-1}

Seconds in 1 year = 365 × 24 × 60 × 60

= 3.153 × 10^{7} seconds

Total distance in 1 light year = speed × time

= 3 × 10^{8} × 3.153 × 10^{7}

= 9.46 × 10^{15} m

1 m = 10^{-3} km

9.46 × 10^{15} m = 9.46 × 10^{12} km

Therefore, Inian and Ezhilan both are right.

**Question 2.**

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

**Answer:**

Here, thickness of the rubber ball = diameter of the ball.

Main scale reading = 7 cm

Vernier scale reading = 6

Least count = 0.01 cm

Assuming, there is no zero error

Diameter of the ball =

Main scale reading (MSR) +

(Vernier scale coincidence (VC) × least count (LC)) ± ZE

= 7 + (6 × 0.01) ± 0

= 7.06 cm

Radius of ball

= 3.53 cm

Hence, radius of the ball is 3.53 cm.

**Question 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.

**Answer:**

Given, Pitch scale reading (PSR) = 1 mm

Head scale coincidence (HSC) = 68

Least count (LC) = 0.01 mm

Assuming no zero error, we get

Corrected Head scale coincidence (CHSC) = 68

Thickness of the coin = PSR + (CHSC × LC)

**=** 1 + (68 × 0.01) mm

= 1.68 mm

Hence, Thickness of the coin is 1.68 mm.

**Question 4.**

Find the mass of an object weighing 98 N.

**Answer:**

weight = mass × gravity

We know that, gravity = 9.8 ms^{-2}

Given, weight = 98 N

= 10 kg

Hence, mass of the object is 10 kg.