SCERT KERALA TEXTBOOKS SOLUTIONS & NOTES: Class 8 Basic Science (English Medium) Chapter 08 Measurements and Units
Textbooks Solution for Class 8th Basic Science (English Medium) | Text Books Solution Physics (English Medium) Chapter 08 Measurements and Units
ഈ അദ്ധ്യായം Malayalam Medium ഉടൻ അപ്‌ലോഡ് ചെയ്യും.
SCERT Solutions for Class 8 Basic Science Chapterwise 
Class 8 Physics - Questions and Answers 
Chapter: 08 - Measurements and Units 
* Measurement.
Measurement is the comparison of a given physical quantity with a convenient or familiar standard of the same physical quantity. That standard value is called unit.
When we measure the length of a table with our forearm (much), we compare the length of the table with our forearm.  And state how many times longer the table than that of the forearm. Now we use ‘length of our forearm’ as the unit for measuring the length of the table.
We use various units for measuring length. Eg:- centimetre, inch, muzham etc.
But the basic unit of length is metre. Its symbol is 'm'.
Centimetre and millimetre are the smaller units of length.
In the metre scale, the distance between two successive long lines is 1 cm and the distance between two successive small lines is one millimetre. 
(1/100)th part of a metre is one centimetre. That is, 100 cm is equal to 1 m.
Similarly, 1000 millimetre is 1 metre.
Kilometre (km), Astronomical unit (AU), Light year (ly) are bigger units of length.
1 km = 1000 m
The astronomical unit is the average distance between the sun and the earth. AU and light year are used to measure the distance to planets and stars respectively. 

* Area of a leaf
Take the leaf and place it on a graph paper and trace the outer edges using a pencil. After removing the leaf, count the number of complete squares and number of squares having half or more. Then the total number of squares will be the approximate area of the leaf. (Area of a square = 1 cm²)
The area is a derived quantity. Its basic unit is m²

* Volume
The space occupied by a body is referred to as its volume.
Volume = length x breadth x height
The basic unit of volume is cubic metre (m³), it is a derived unit.

* Density
The mass per unit volume of a substance is referred to as its volume.
Density= Mass / Volume
Unit: kg/m³. It is a derived unit.

* Fundamental quantities and fundamental units.
Quantities which are not related to one another and cannot be expressed using other quantities are called fundamental quantities. Length, mass, time, Electric current, Temperature, amount of substance and luminous intensity are the fundamental quantities. The units of fundamental quantities are fundamental
units. The system based on these fundamental units is called SI units.
Fundamental quantities and their units are tabled below.

1. If petrol, diesel etc catches fire one should never try to extinguish it using water. Why?
Ans: Because petrol, diesel etc have a lower density than water. So it floats over water. That is why we cannot extinguish using water.

2. Find the density of an object of mass 60 kg having length 5 m, breadth 3 m and height 2 m?
Ans: 
Density = Mass / Volume
Volume = l x b x h = 5 x3 x2 = 30 m³
Density = 60/ 30 = 2 kg/m³

* Observe the units of different in measurements written by a student in her science diary. correct the wrong units.
a) 75 cms, b) 10 m/s²   c) 15Kg/m³  d) (d) 10 m 25 cm (e) 5 newton (f) 100 m
Ans.
(a) 75 cm
(c) 15 kg/m³
(d) 10.25 m 

* The units of Fundamental quantities are Fundamental units.
(a) What is the fundamental unit of length?
(b) What is the derived unit?
(c) Find out the derived units of Area and Density?
Ans.
(a) m
(b) defenition
(c)m², kg/m³ 

* A solar day is the time period from one noon to the next noon.
(a) What is the unit of time?
(b)How many seconds make a solar day?
Ans.
(a) Second
(b) 24 x 60 x 60 second 

* 1 quintal = 100 kg
1 tonne = ?
Ans.1000 kilogram.  

* Various units of mass are given below. Write these units in ascending order.
quintal, milligram, tonne, gram, kilogram
Ans. milligram, gram, kilogram, quintal, tonne 
* Teacher is drawn different types of lines on the board with chalk. Write a method to find out the length of a curved line?
Ans. Using a thread and meter scale
eg. The length of the curve cannot be measured directly using a metre scale.
Here we can adopt a technique with a twine. For this place, a twine gently along the curve from A to B. Then measure the straight length of the twine.

* In the class you have seen the experiment to find out the diameter of spherical objects.
Write the procedure of the experiment to find out the diameter of a tennis ball?
Ans. Take two wooden blocks and insert the ball in between them. Take the diameter of the ball by measuring the gap between the wooden blocks using a scale.
* Write the method you adopt to find out the thickness of a thin wire having a one-meter length
Ans. Wind the wire over a pencil and find out the total thickness. Divide it by the number of turns.

* Thickness of a 100 paged science diary is measured using a scale and the value is 1.2 cm
a. Find out the thickness of a paper in the science diary?
b. convert this value of thickness into SI unit
Ans.
a. 0.012 cm
b. 0.00012 m 
(Suppose you are asked to measure the thickness of one sheet of a notebook using a scale in your instrument box. Here the direct measurement is impossible. In these situations, we follow other convenient methods. In this case, we take the height of a bundle of sheets. Then divide the height with the number of sheets in the bundle. This will be the thickness of one sheet.
Example: Thickness of a bundle of 50 sheets is 6 mm. Find the thickness of one sheet.
Ans. Thickness of one sheet = 6/50 = 0.12 mm) 

* Different measurements of lengths are tabulated here. Fill in the blanks 

 millimetre

 centimetre

 meter

 100 mm

 A

 0.1 m

 B

 500 cm

 5 m

 1000 mm

 100 cm

 C
Ans.
A = 10 cm
B = 500 mm
C = 1 m 

* Measuring jar marked 10 ml is in the figure
a) In both the measuring jar do the least count is same?
b) Find out the least count of the jar named D
Ans.
a. yes
b. 0.2 ml 

* Device used to find out the time using shadow is in the figure
a. Identify the device?
b. What is the main defect of this device?
Ans.
a. Sundial
b. It cannot be used in night 



* Correct the statements if it is wrong
- Quantity of matter in an object is its mass
- A solar day is the time period from one noon to the next noon
- Fundamental unit of time is hour
Ans. Fundamental unit of time is second 

* Different measures of distance are given below. Arrange them in descending order.
(micrometre, astronomical unit, meter, parsec)
Ans. parsec, astronomical unit, meter, micrometre 

* To measure the distance to planets and stars some units like astronomical unit(AU), light-year(ly). parsec(pc) is used
a. What do you mean by astronomical unit (AU)?
b. How much a light-year is one parsec?
Ans.
a. The average distance from the earth to the sun is AU. This is equal to 15 crore km
b. 3.26 light year 
* Find out the correct units from the following. Write the reasons of  your conclusion
kg/m³, kg per m³, kilogram per cubic meter, kilogram/m³
Ans.
kg/m³,  kilogram per cubic meter
Do not write both the name of the unit and its symbol at a time 

* Convert the following measurements into SI units without a change in their values.
a) (200 cm, 4000g, 2.5 km, 2 h)
b) Write the properties of SI units
Ans.
a) 2 m, 4 kg, 2500 m, 7200 s
b) Unified units
internationally accepted
Adequate to express all physical quantities

* Water and kerosene is taken in the beaker is shown in the figure
a) Identify A and B. Justify
b) If petrol or kerosene get caught fire. It is not good to extinguish this using water. Why?
Ans.
a). A= kerosene, B= water, A has low density than B
b). petrol and kerosene have less density than water. So when water is used for extinguishing, kerosene and petrol float over water, Then it caught fire.

* What is the basic unit of length? Write down its symbol.
Ans. metre (m)

* What is the least count? Give the least count of the metre scale.
Ans. Least count of a device is the smallest measurement that can be accurately measured using the device is called its least count.  Least count of metre scale is 1 mm.

* We use so many units other than metre for measuring distance for a various practical purpose.
a. What is known as the average distance from the earth to Sun? 
b. Define light year. Express one light-year in kilometre.
c. Which are the units suitable for measuring the distance between stars?
d. 'parsec' is the largest unit of length. How many light years is equivalent to one parsec?
c. The thickness of plastic carry bag is too small. Which is the unit suitable for stating its thickness?
Ans.
a. Astronomical unit.   
b. One light-year is the distance travelled by light in one year. It is equal to
9460800000000 km  (9.46x10¹² km)
c. light year and parsec.
d. 3.26 light year.
e. nanometre

* Common balance is used for measuring mass.
a.What is mass? What is its basic unit?
b. Write down two smaller units of mass. How are they related to the basic unit of mass?
c. How many kilograms is one tonne?
Ans.
a. Mass of a substance is the measure of matter contained in it. the kilogram is the basic unit of mass.
b. gram and milligram.
1000 g = 1 kg   1000000 mg = 1 kg
c. 1 tonne = 1000 kg

* Units expressed in terms of basic units are called derived units.
a. Write down a derived unit which is expressed using the metre. What is this unit for?
b.What is the unit of density? What are the basic units involved in it?
Ans.
a. m²: Unit of area
b. kg/m²
kilogram and metre are used in this derived unit.
Basic Science Textbooks (pdf) - Click here 

ഈ ബ്ലോഗിലെ എല്ലാ പോസ്റ്റുകളും ഒരുമിച്ച് കാണാനും ആവശ്യമുള്ളവ എളുപ്പത്തിൽ തിരഞ്ഞെടുക്കാനും ഇവിടെ ക്ലിക്കുക.
PSC Solved Question Papers ---> Click here 
PSC TODAY's EXAM RESULTS ---> Click here
PSC EXAM PROGRAMME -> Click here
CURRENT AFFAIRS QUESTIONS -> Click here
PSC Degree Level Questions & Answers - Click here
PSC LDC/LGS Questions & Answers - Click here
PSC RANK LISTS / SHORTLISTS -> Click here
PDF BOOKS - Click here
TEACHING APTITUDE TEST (K-TET, C-TET,, etc.) ---> Click here