Measurement and Units Class 8 Questions and Answers Notes Basic Science Chapter 1 Kerala Syllabus

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Class 8 Basic Science Chapter 1 Measurement and Units Question Answer Notes

Class 8 Basic Science Chapter 1 Notes Kerala Syllabus Measurement and Units Question Answer

Measurement and Units Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
Identify the odd one out in each group and explain common features of the others.
I a) Kilogram b) Kilometre c) Second d) Mole
II a) Time b) Area c) Mass d) Electric current
III a) Metre b) Kilogram c) Second d) Degree Celsius
Answer:
I. b) Kilometre
Kilometre is a unit of length. Others are SI unit of mass, time and amount of substance respectively.

II. b)Area
Area is a derived quantity. Others are fundamental quantities.

III. d) Degree Celsius
This is a unit of temperature. Others are SI unit of length, mass and time respectively.

Question 2.
Different units of length are given below. Fill in the table below.

Answer:

Unit	Relationship with metre
Kilometre	1 km = 1000 metre
Millimetre	1 m = 1000 millimetre
Centimetre	100 cm = 1m

Question 3.
Convert the following measurements to SI units without changing their values.
a) 2000 g
b) 1 h
c) 1.5 km
d) 200 cm
Answer:
a) 2000 g = \(\frac{2000}{1000}\) = 2 kg
b) 1 h = 60 × 60 = 3600 s
c) 1.5 km= 1.5 × 1000 = 1500 m
d) 200cm = \(\frac{200}{100}\) = 2m

Question 4.
Different units of mass are given below. Arrange them in the ascending order of their values.
a) Kilogram
b) Milligram
c) Quinta
d) Gram
Answer:
b) Milligram < d) Gram < a) Kilogram < c) Quintal

Basic Science Class 8 Chapter 1 Question Answer Kerala Syllabus

In our daily life, it is necessary to measure and state the characteristic properties of objects and phenomena. Such measurable quantities are physical quantities.
Question 1.
Observe the following situations in our life. Find the physical quantities in each of them.


Record the quantities you identified, in the table.
Answer:

Situation	Physical quantity
1. Measuring the depth of a pit	Length
2. Measuring the weight of vegetables	Mass
3. Taking measurements by a tailor	Length
4. Using a stopwatch in a race	Time
5. Measuring blood pressure	Pressure
6. Measuring body heat	Temperature

Question 2.
Find and write more physical quantities that you are familiar with.
Answer:

• Electric current
• Amount of substance
• Luminous intensity

All the physical quantities cannot be measured directly. In situations where direct measurement is not possible, we can write them with reference to other physical quantities.

Question 3.
Find out the physical quantities mentioned in the table 1.1 and list them below.
Answer:

1. Length
2. Mass
3. Time
4. Temperature

Question 4.
Look at the pictures. What are the physical quantities in these situations?

Answer:
• Area
• Volume

Question 5.
Record how each of them is found out and complete the table appropriately.

Answer:

Situation	Physical Quantity	Method of Finding
For painting the wall	Area	Area = Length × Width
Measurement of medicine/liquid	Volume	Volume = Area of the measuring jar × Height

a) Which are the quantities used here to find area and volume?
Answer:
Length, width, area and height.

b) All of them are distances between two positions, aren’t they?
Answer:
Yes. All of them are distances between two positions.

The distance between two positions represents a physical quantity called length. We have used the fundamental quantity of length to find the quantities of area and volume. Such quantities that can be found out using fundamental quantities are called derived quantities.

Quantities that can be expressed in terms of fundamental quantities are derived quantities.

See, how the mass is marked on a gas cylinder.

Mass marked on the cylinder = 14.2 kilogram
Here, the physical quantity of mass is indicated using a numerical value i.e., 14.2 (magnitude) and a unit i.e., kilogram.

Question 6.
Similarly, complete the table with the physical quantities shown in the pictures below, along with their numerical values and units.

Answer:

Situation	Physical quantity	Numerical Value	Unit	Mode of marking measurements
Fig. 1.12	Temperature	37.8	Celsius	37.8° C
Fig. 1.13	Height	165	Centimetre	165 cm
Fig. 1.14	Mass	1	Kilogram	1kg

A physical quantity is expressed by a number indicating its value followed by its unit.

Question 7.
Tabulate the measurements from both the activities.

Answer:

Activity	Physical quantity	Reference object used for measurement	Recorded quantity
Measuring the height of the child	Length	Longer stick	2 stick
		Shorter stick	6 stick
Measuring the quantity of water	Volume	Larger glass	5 glass
		Smaller glass	10 glass

Question 8.
Analyze the table. Two different reference objects were used in each case to determine a physical quantity.
a) In both cases, are the measurements obtained the same?
Answer:
No, the measurements obtained are not the same.

b) Why are the measurements not equal?
Answer:
It is because the reference object used for each measurement is different.

c) When everyone uses the same reference object, isn’t measurement the same?
Answer:
When the same reference object is used, the measurement is the same.
When a physical quantity is measured anywhere in the world, the measurement should be the same. For this, everyone should adopt a fixed reference. This is called the unit of a physical quantity.

A unit is a standardised reference accepted universally to measure a physical quantity.

In the past, different units were used for measurement and recording in each region. For example, units like the foot, cubit and hand span were used locally to measure length.

Question 9.
Different units were also used in other countries. What would be the practical problems of using different units in different countries?
Answer:

• Low accuracy
• Difficulty for the people in other regions to analyse measurements.
• Lack of uniformity
• Difficulty with transaction

Today, the unit ’metre’ is used everywhere in the world to measure length.

There are internationally accepted units for all physical quantities. This is called the International System of Units, abbreviated as ‘SI’ units. Measurement using the SI units always has a universal result.

Now we can understand that with the help of SI units which always, has a universal result, parts of vehicles and equipment we use, even if manufactured in different countries can be perfectly assembled in any factory in the world.

Different units are required for the same physical quantity in various contexts. Larger units are used for larger quantities and smaller units for smaller quantities.

Question 10.
Now complete the following relationship given below.
Answer:
1 metre = 100 centimetre
1 centimetre = 10 millimetre
1 metre = 1000 millimetre
There are situations where we have to use smaller measurements.

Question 11.
Pay attention to the notice of a municipality.

Prohibited The sale of plastic bags below 30 micron is prohibited in shops within the limit of the municipality with effect from 30.10.2022.

What is the measurement mentioned in the notice?
Answer:
The measurement mentioned is micron. Micron is the abbreviation of micrometre.

Question 12.
How many micrometres would make one metre?
Answer:
1 metre = 1000000 micrometre

There are also situations where we need units larger than metre.
The abbreviation “km” on the traffic sign stands for kilometre.
1 kilometre = 1000 metre
Are there situations where we need even larger units? Read the following excerpt from a science article.

Scale of the Solar System Astronomical Unit (AU) is the average distance from the Earth to the Sun. It is approximately 150 million kilometre. A light year is the distance light travels in a year in vacuum. Light travels at a speed of approximately 300,000 km/s.

Question 13.
Discuss the situations where the units mentioned in the article are used.
Answer:
Astronomical unit is used to measure the distance between Earth and the Sun, distance from Sun to different planets and distance between planets in our solar system. Light year is used to measure the distance between Earth and stars, distance between galaxies or stars.

Question 14.
Look at the picture of weighing apples in a shop. The weight is measured by placing weight blocks on one side of the scale.

Here, why are weight blocks placed on one side?
Answer:
This is done to ensure that the apples taken have the same mass as weight of blocks.

The amount of matter contained in a substance is its mass.

Question 15.
Examine the picture of the weight blocks shown in figure below. What is written on them?

Answer:
The mass of the weight block is written on them

The unit of mass is the kilogram. Its symbol is ‘kg’.

We need units other than kilogram for mass.

Question 16.
You might have noticed the quantity of toothpaste and tablet printed on their packages. What does it mean?

Answer:
The quantity printed on them indicates their mass.

Milligram and gram are the smaller units of mass. 1 gram = 1000 milligrams

Question 17.
You might have seen trucks carrying load. Which are the larger units commonly used in such situations?
Answer:
Quintal and tonne are the larger units of mass commonly used in such situations.
Identify the relationship between the units of mass and kilogram from the table given below.

Unit	Relation to kilograms
Milligram	1 kilogram = 1000000 milligram
Gram	1 kilogram = 1000 gram
Quintal	1 quintal = 100 kilogram
Tonne	1 tonne = 1000 kilogram

Question 18.
Minute and hour are the other units used to denote time. Identify the relationship between these units and ‘second’.

Answer:

Unit	Relationship with second
Minute	1 minute = 60 second
Hour	1 hour = 3600 second

Question 19.
The figure shows thousand cubes each with sides of 1 cm arranged to form a large cube.

If volume of the large cube is 1 litre. Can you complete writing the relationship between various units based on the figure?
Answer:
1 litre = 1000 cm³
1 litre = 1000 millilitre

Question 20.
Take a cardboard box and calculate its volume. Fill it with sawdust and measure its mass. Then replace it with sand and find its mass. Tabulate the findings.

Answer:

Substance	Mass	Volume	\(\frac{\text { Mass }}{\text { Volume }}\)
Sawdust	30 g	200 cm3	\(\frac{30}{200}\) = 0.15 g/cm3
Sand	320 g	200 cm3	\(\frac{320}{200}\) =1.6 g/cm3

The mass of a substance per unit volume is called its density. Density = \(\frac{\text { Mass }}{\text { Volume }}\)

In the table given, even though the volume of sawdust and sand is the same, see how the mass per unit volume is calculated.

If volume is the same, objects with higher mass will have higher density. In the case of a particular substance, density is a fixed number.

Question 21.
Why is density displayed on the fuel dispenser in a petrol pump?
Answer:
Displaying density on the fuel dispenser in petrol pumps helps to check if the fuel is pure and not mixed with anything. If the fuel is adulterated with some impurities, then the density will change. To ensure that it is not adulterated, the density is displayed.

Question 22.
What are the characteristics of SI units?
Answer:

• They are standardised units.
• They are internationally accepted.
• Units of all other quantities can be expressed in terms of these units.

Question 23.
The table below shows common errors that may occur when writing units. Compare each of these with the correct version and suggest a general rule for each.

Answer:

Unit written incorrectly	General rules
1000 KG/M3 1.5 KG	Use lower case of the English alphabet.
1000 kgs/m3 1.5 kgs	Do not use the plural form for symbols.
1000kg/ m3 1.5kg	While writing units along with a numerical value, there must be a single space between them.
1000 kg/m/m/m	Do not use more than one slash in one derived unit.
1000 kg/ cubic metre 1000 kilogram per m3	Do not mix a symbol of a unit with the name of a unit.
1 kg 500 g	Do not use more than one unit to express a physical quantity.
273 Kelvin	Use only lowercase letters when writing the name of a unit instead of its symbol.

Now let us get familiar with some other rules.

Physical quantity	Correct method	Incorrect method	Rule
Force	N	n	The symbols of the units formed from the names of individuals should be written using uppercase of the English alphabet.
Length	60 cm is the length of the desk.	60 cm. is the length of the desk.	No full stop or comma should be used after the symbol. They can be used at the end of the sentence.
	The length of the desk is 60 cm.	The length of the desk is 60 cm
Energy	N.m Nm	Nm	A full stop/space should be used between the units formed as multiples of units.

Question 24.
What are the rules to be followed internationally when writing units and their symbols?
Answer:

1. Use lower case of the English alphabet to write the symbol of the units.
   e.g. 1000 KG/M³– wrong, 1000 kg/m³ – correct
2. Use only lowercase letters when writing the name of a unit.
   e.g. 273 Kelvin-wrong, 273 kelvin- correct
3. The symbols of the units formed from the names of individuals should be written using uppercase of the English alphabet.
   e.g. The unit of the physical quantity force is newton. This is named after sir Isaac Newton. The symbol is denoted as N.
4. While writing units along with a numerical value, there must be a single space between them, e.g. 1.5kg- wrong, 1.5 kg -correct
5. Do not use the plural form for symbols.
   e.g. 1.5 kgs- wrong, 1.5 kg -correct
6. Do not use more than one slash in one derived unit.
   e.g. 1000 kg/m/m/m -wrong, 1000 kg/m³– correct
7. Do not mix a symbol of a unit with the name of a unit.
   e.g. 1000 kg/ cubic metre-wrong, 1000 kg/m³– correct, 1000 kilogram per cubic metre (correct)
8. Do not use more than one unit to express a physical quantity.
   e.g. 1kg 500 g (wrong) 1.5 kg ( correct)
9. No full stop or comma should be used after the symbol. They can be used at the end of the sentence, e.g. 75 cm is the length of a table, (correct) 75 cm. is the length of a table, (wrong)
10. A full stop/space should be used between the units formed as multiples of units, e.g. Nm – wrong, N.m or N m – correct

Question 25.
What are the instruments used to measure length?
Answer:
Scale, tape.

Question 26.
Look at the picture given.

a) Measure the length of a pen using a scale and write it down.
b) Also, use a measuring tape to determine your height.
c) What is the unit on the scale/tape used?
d) What is the smallest measurement possible using the scale/measuring tape?
Answer:
a) Length of the pen = 14.7 cm
b) Your height = 138 cm
c) Centimetre
d) 0.1 cm

The smallest value that can be measured using an instrument is called its least count.

Question 27.
The least count of a commonly used scale is 0.1 cm . Are there instruments with a least count smaller than this? Find out and write.
Answer:
Vernier caliper is an instrument used to measure the length of rod, diameter of a cylinder or sphere shaped object etc. Least count: 0.01 cm (or 0.1 mm)
Screw gauge is an instrument used to measure the thickness of glass plates and diameter of thin wires. Least count – 0.001 cm (or 0.01 mm).

Question 28.
The figure shows some papers stacked together.

Measure the thickness of the paper stack and write it down.
Answer:
Number of papers in the paper stack = 50
Thickness of the paper stack = 5 cm
Thickness of one paper = \(\frac{\text { Thickness of the paper stack }}{\text { Number of papers }}\) = \(\frac{5}{500}\)
= 0.01 cm = 0.01 mm

Question 29.
What unit is used in the measuring jar?
Answer:
millilitre

Question 30.
What is the least count of the measuring jar?
Answer:
l ml
Initial water level before dipping the stone = 50 ml
Water level after dipping the stone = 78 ml
Volume of the stone = 78 – 50 = 28 ml

Class 8 Basic Science Chapter 1 Question Answer Extended Activities

Question 1.
Identify the different units used in our locality for measuring length and mass in the past.
Answer:
Some of the different units used in our locality for measuring length and mass in the past are tabulated.

Unit of length	Unit of mass
Vaara Muzham Feet Kol Furlong Mile	Chan Kizhi Edangazhi Nazhi Para Padi

Question 2.
Prepare a seminar paper on the rules to be followed when writing ‘units’.
Answer:
Title: Rules to be followed when writing units.

Introduction: In our day to day life and in science, we make use of different units to measure various physical quantities like length, mass, time etc. A physical quantity is expressed by a number indicating its value followed by its unit. It is very important to express units in the right way to avoid confusion and to maintain accuracy in measurements.

Rules to be followed when writing units
1. The symbols of units are normally written using small letters in the English alphabet.
e.g. m (metre), s (second)

2. The symbol of units named after persons should be expressed by capital letters of the English alphabet.
e.g. The unit of the physical quantity electric current is ampere. This is named after Andre-Marie Ampere. The symbol is A.

3. While writing the names of units never use capital letters.
e.g. kelvin (correct) Kelvin (wrong)

4. Never use the plural form for symbols.
e.g. 10 kg (correct) 10 kgs (wrong)

5. Never use full stop or comma after a symbol except at the end of a sentence.
e.g. 75 cm is the length of a table. (correct)
75 cm. is the length of a table, (wrong)

6. While writing derived units a slash (/) is used to denote division. But never use more than one slash in one derived unit.
e.g. m/s² (correct) m/s/s (wrong)

7. When a derived unit is expressed as the product of other units use a dot or a space between them, e.g. N.m or N m

8. Do not mix the name of a unit with the symbol.
e.g.kg/m³ (correct)
kilogram per cubic metre (correct)
kg/cubic metre (wrong)
kilogram per m³ (wrong)
kg per m³ (wrong)
kilogram/m³ (wrong)

9. While writing units along with a numerical value, there must be single space between them, e.g. 273 K (correct), 273K (wrong)

10. Never use more than one unit to express a physical quantity, e.g. 10.25 m (correct) 10 m 25 cm (wrong)

Conclusion
Following these rules will help us to write the units in its clear and correct manner so that it can be understood by all.

Measurement and Units Class 8 Notes

Class 8 Basic Science Measurement and Units Notes Kerala Syllabus

• Fundamental quantities are quantities that exist independently and cannot be expressed in terms of other quantities.
• Quantities that can be expressed in terms of fundamental quantities are derived quantities.
• A physical quantity is expressed by a number indicating its value followed by its unit.
• A unit is a standardised reference accepted universally to measure a physical quantity.
• There are internationally accepted units for all physical quantities. This is called the International System of Units, abbreviated as ‘SI’ units. Measurement using the SI units always has a universal result.
• The SI unit of length is metre. Its symbol is ‘m’. Centimetre, millimetre, kilometre, etc. are the other units of length.
• The amount of matter contained in a substance is its mass. The unit of mass is the kilogram. Its symbol is ‘kg’. Milligram and gram are the smaller units of mass.
• Quintal and tonne are the larger units of mass commonly used.
• The SI unit of time is the second. Its symbol is ‘s’.
• Minute and hour are the other units used to denote time.
• The volume of an object is the amount of space it occupies. The SI unit of volume is cubic metre.
  It’s symbol is m³.
• The mass of a substance per unit volume is called its density. Density = \(\frac{\text { Mass }}{\text { Volume }}\)
• Fundamental units are the units of fundamental quantities.
• Characteristics of SI units
  • They are standardised units.
  • They are internationally accepted.
  • Units of all other quantities can be expressed in terms of these units.
• Derived units are units that can be stated using fundamental units or that depend on fundamental units.
• The smallest value that can be measured using an instrument is called its least count.

INTRODUCTION

In our daily life, we often need to measure physical quantities like length, mass and time. In some situations, it is very important to be accurate in these measurements. Long ago, people had many problems because they did not have accurate ways to measure, and different places used different types of measuring scales. This caused confusion and mistakes. This chapter deals with fundamental quantities and derived quantities, units of physical quantities, fundamental and derived units, rules for writing the units and measuring instruments.

FUNDAMENTAL QUANTITIES AND DERIVED QUANTITIES

There are many physical quantities. Among them length, mass, time, electric current, temperature, amount of substance and luminous intensity are called fundamental quantities. All other quantities can be expressed in terms of these fundamental quantities.

Fundamental quantities are quantities that exist independently and cannot be expressed in terms of other quantities.

UNITS OF PHYSICAL QUANTITIES
Activity

• Mark the height of a child in your class on the wall using a pencil as shown in the figure 1.5. Each one in the class may measure the height using two sticks of different lengths.
• Fill a bucket with water. Measure the water in it with two glasses of different sizes (Figure 1.16).

DIFFERENT UNITS OF LENGTH

The SI unit of length is metre. Its symbol is ‘m’. Centimetre, millimetre, kilometre, etc. are the other units of length.

The picture shows part of a metre scale.

Take a metre scale from the science lab and examine it. You can see small and large lines on the metre scale. The distance between two consecutive large lines is one centimetre and the distance between small lines is one millimetre.

DIFFERENT UNITS OF TIME

The SI unit of time is the second. Its symbol is ‘s’.

VOLUME

The volume of an object is the amount of space it occupies. The SI unit of volume is cubic metre. It’s symbol is m3.

FUNDAMENTAL AND DERIVED UNITS

FUNDAMENTAL UNITS
In 1960, an international conference held in Paris approved the International System of Units or SI units as the universal system of units for measurements. Under this system, units were assigned to all the fundamental quantities.

Fundamental units are the units of fundamental quantities.

Note the fundamental units and their symbols given below.

DERIVED UNITS
We have learned about derived quantities. Such as volume and density, whose units are obtained from fundamental units.

We can write the derived units by relating fundamental units one another. Derived units are formed using fundamental units.

See how derived units are formulated in the table given.

Derived quantities	Equation	Unit
Area	Area = length × breadth	m × m = m2
Volume	Volume = length × breadth × height	m × m × m = m3
Density	Density = \(\frac{\text { Mass }}{\text { Volume }}\)	kg/m3

Derived units are units that can be stated using fundamental units or that depend on fundamental units.

RULES FOR WRITING THE UNITS
Observe the correct notation of units for two physical quantities.

Quantity	Unit
Mass of 1.5 litre of water	1.5 kg
Density of water	1000 kg/m3 1000 kilogram per cubic metre

MEASURING THE VOLUME USING A MEASURING JAR
Let’s try to find the volume of a stone. Pour some water into a measuring jar and mark its level. Tie the stone with a thread and dip into the water. Observe the rise in the water level. From this, we can calculate the volume of the stone which is equal to the volume of water displaced.

MEASURING TIME USING A STOPWATCH
A stopwatch is used to measure a time intervals. As shown in the figure, tie a metal ball using a thread and hang it. Pull the ball slightly and release it to oscillate. Observe the motion. Measure the time taken for 10 oscillations using a stopwatch. Record the measurement.

Time required for 10 oscillations = 10 s
A good understanding of physical quantities will help you in further studies and on the proper use of measurement and units in daily life.