Unit 1 - Measurement - Class 8 & 9

1.      What do you mean by physical quantities?

-          Those quantities which can be measured and can be expressed in terms of some numerical value are called physical quantities. For example: length, mass, time etc.

2.      Why love, sympathy, anger etc are not physical quantities?

-          These cannot be expressed in terms of some numerical value. So these are not physical quantities.

3.      What is measurement?

-          The comparison of unknown quantities with same standard quantities is known as measurement.

4.       What is the importance of measurement in our daily life?

-          Measurement has very important role in our daily life in the following way:

a.       To conduct scientific experiments.

b.      To simplify trade and transactions

c.       Taking proper medicines.

d.      Cooking properly.

e.       To get accurate time.

f.       For sports.

g.       For transportation. Etc

5.      Why we cannot imagine our daily life without measurement?

-          Measurement is very useful in our various sector of life as scientific study, trade, medicine, cooking, sports, time, transportations etc. So we cannot imagine our daily life without measurement.

6.      What do you mean by fundamental quantities?

-          Those quantities which are independent of other quantities are fundamental quantities. For example: length, mass, time etc. ( In another language the quantities which can neither be formed nor can be divided into other quantities are called fundamental quantities.)

7.      What do you mean by derived quantities?

-          Those quantities which can only be formed with the help of fundamental physical quantities are known as derived quantities. For example: area, volume, speed etc.

8.      Differentiate between fundamental and derived physical quantities.

(Instructions to students: in the section of differentiate questions, you need to show comparative points not definitions. And you should not show the points which cannot be compared. For example if you are showing the difference between you and your friend, then don’t compare eye and hand, compare eye and eye, hand to hand, foot to foot. I hope you understood)

(Dear students! the question is about quantities, so be careful, don’t include units.)

-          The difference between fundamental and derived physical quantities are as follows:

Fundamental Physical Quantities	Derived Physical Quantities
1.      These are independent to other quantities.	1.      These are dependent on fundamental physical quantities.
2.      These are 7 in number.	2.  These are numerous.
3.      These can be measured directly.	3.  These can’t be measured directly. Parent quantities should be measured first.
4.      For example: Length, mass, time etc.	4.  For example: Area, volume, speed etc.

9.      What do you mean by unit of measurement?

-          The unit of measurement is defined as the definite magnitude of quantity which is used as a reference for the measurement. For example, unit of length is Meter; unit of time is Second etc.

10.  What do you mean by fundamental units?

-          Those units which are independent of other units are called fundamental units. For example: meter (m), kilogram (Kg), second (s), ampere (A), candela (Cd), mole (Mol), Kelvin (K).
( In another language fundamental and derived quantities can be defined as given in video)

11.  What do you mean by derived units?

-          Those units which are dependent on fundamental units are called derived units. For example: m/s², m³, kgm^-3etc,

12.  Differentiate between fundamental and derived units.

-The differences between fundamental and derived units are as follows:

Fundamental Units	Derived Units
1.      These are independent of other units.	1.   These are dependent on fundamental units.
2.      These are 7 in numbers.	2. These are numerous.
3.      For example: meter, second, kilogram, candela, mole, ampere, Kelvin.	3. For example: m/s, kg/m3 etc.
4.      These are the units of fundamental quantities.	4. These are the units of derived quantities.

13.  Define MKS (Metric System) System.

-          The system of measurement in which length is measured meter, mass is measured in kilogram and time is measured in second is known as MKS System.

14.  Define CGS System.

-          The system of measurement in which length is measured in centimeter, mass is measured in gram and time is measured in second is known as CGS System.

15.  Define FPS System.

-          The system of measurement in which length is measured in foot, mass is measured in pound and time is measured in second is known as FPS System.

16.  Why unit of density is called as a derived unit?

-          The unit of density (kg/m³) is obtained from two fundamental units: kg and m. So it is called as a derived unit.

17.  Why unit of power is called as a derived unit?

-          The unit of power (kgm²/s³) is obtained from three fundamental units: kg, m and s. So it is called as a derived unit.

(Dear students you may be asked similar type of questions as pressure, work, momentum, velocity, acceleration, area etc. which are to be answered like above illustrations.)

18.   What is SI System?

-          The International System of units which is accepted all over the world is known as SI System. SI system uses seven fundamental units which are meter (m) of length, kilogram (Kg) of mass, second (s) of time, ampere (A) of current, candela (Cd) of luminous intensity, mole (Mol) of amount of substance and Kelvin (K) of temperature.

(Dear students if this question is as very short type, give only one line answer and if asked as a long question give all description.)

19.  What are the advantages (benefits) of SI System?

-          Following are the advantages of SI System:

a.       It brings uniformity in measurement globally.

b.      It minimizes discrepancy and false measurement.

c.       It is rational; it uses only one unit for one physical quantity.

d.      It is coherent; all derived units can easily be derived.

e.       Multiples and sub multiples can easily be expressed in terms of power of 10.

20.  Why SI system is called as extended system of MKS system?

-          It is because SI system includes seven fundamental units meter, kilogram, second, Kelvin, ampere, candela and mole which includes three fundamental units meter, kilogram and second. So SI system is called as extended system of MKS system.

21.  Measurement scales in the market should be re-calibrated by government regularly, why?

-          It is to stop the discrepancy in the measurement and false measurement by traders.

22.  What are the differences between SI and MKS system?

-Following are the differences between SI and MKS system:

SI System	MKS System
1.      It uses 7 fundamental units	1.      It uses only three fundamental units.
2.      It covers all needs of measurement in Science, Engineering and Commerce.	2.    It covers only mechanics and traditional commerce.

( What do you mean by unit? Ans.: Magnitude of measurement is known as unit.)

23.  What do you mean by mass? (Questions onward for class 8)

-          It is amount of matter contained in a body. It depends on the number of atoms and its atomic mass.

24.  What do you mean by standard mass of 1Kg?

-          It is defined as the mass of an international sample of a cylinder made of platinum-iridium which is kept at the International Bureau of Weights and Measures.

25.  What is gravity?

-          The force which attracts body towards the centre of the earth is known as gravity. Unit of gravity is m/s².

26.  What do you mean by weight?

-          The net force of gravity acting on a body is known as weight.

Unit of weight is Newton (N). It can be calculated as: W = m x g. (where, w = weight, m = mass and g = gravity, g = 9.8m/s²)

27.  Write down the differences between mass and weight?

-          The differences between mass and weight are as follows:

Mass	Weight
1.      It is total amount of matter contained in a body.	1.  It is net force of gravity acting on a body.
2.      Mass of a body remains constant everywhere.	2.  Weight of a body changes from place to place.
3.      It is scalar quantity.	3.  It is a vector quantity.
4.      Unit of mass is Kg.	4. Unit of weight is Newton (N).
5.      It is measured by using pan balance.	5. It is measured by using spring balance.

28.  Why does weight of a body changes from place to place?

-          It is due to effect of gravity. The place where the acceleration due to gravity is more, weight of a body becomes more and the place where the acceleration due to gravity is less, weight of a body becomes less.

29.  What do you mean by zenith?

-          The imaginary point in the sky just above our head when we stand straight is known as zenith.

30.  What is one solar day?

-          The time taken by the earth to rotate once on its own axis is known as one solar day.

(In another word the time taken by the sun to reach again in the same zenith when it moves once from it is known as one solar day.)

          (The time interval between two successive transits by the sun of the meridian directly opposite that of the observer is known as one solar day.)

You can write any one of your choice.

31.  What do you mean by 1 second time?

-          1/86400 part of one solar day is defined as 1 second.

       ( 1 Solar day = 24 Hrs

                            = 24 x 60 min

                                        = 24 x 60 x 60 s

                                        = 86400 s )

CONVERSION OF UNITS

For conversion of units following points to be remembered:

-          First identify in which unit we are converting, into smaller or into larger. For example: 5 km into meter: larger into smaller, 120 seconds into minute: smaller into larger.

-          Find out the relationship between units means 1 larger unit = how much smaller unit. 1km = 1000m and 1 min = 60s as given in example.

-          Multiply with smaller units to convert into smaller unit. 5km = 5 x 1000m = 5000m.

-          Divide with smaller units to convert into larger unit. 120 seconds = 120/60 min = 2 min.

32.  Convert 36 km/hr into m/s. (or covert 36km/hr into SI unit)

-          36km/hr = (36x1000)/(60x60) = 36000/3600 = 10m/s

33.  Convert 15000kg/m³ into g/cm^3.

-          15000kg/m³ = (15000x1000)/(100x100x100) = 15000000/1000000 = 15g/cm³

-          GOOD LUCK  -

Thanks for reading. Please don’t forget share any suggestions, comments and questions its my humble request.