Measurement

C8 1.Measurement

1. Define physical quantity with examples.
Ans: The quantity which can be measured directly or indirectly is called physical quantity.
For example: Length, Mass, Time, Luminous Intensity, etc.
2. Write the types of physical quantities.

Ans: There are two types of physical quantities.They are:
-Fundamental physical quantity
-Derived physical quantity
3. Define area and volume.

Ans: The surface covered by an object is called area.
The space occupied by an object is called volume.
4. What do you mean by fundamental physical quantity and derived physical quantity? Give examples of each.

Ans: Those physical quantities which do not depend upon other physical quantities and exist independently are called fundamental physical quantities.For example : length, time, temperature, Mass, etc.
Those physical quantities which are to be expressed in terms of other fundamental quantities or exists by combination of fundamental quantities are called derived physical quantities. For example: area, velocity, volume, density, acceleration, etc.
5. Define measurement and unit.

Ans. The process of comparing a physical quantity with known standard quantity of the same kind is called measurement.
Unit is a fixed definite quantity which is used as standard of reference to measure the quantity of same kind.
6. What do you mean by SI unit?

Ans: The extended form of MKS system which is derived in order to maintain uniformity in the measurement of fundamental quantities is SI unit. It consists of seven fundamental units. They are Kilogram (kg), meter(m), second(s), candela (cd), ampere(a), mole(mol), Kelvin(K).
7. What is the importance of measurement?

Ans: The importance of measurement are as follows:
-It helps in buying and selling of goods.
-It is important in performing scientific experiments to establish truth about the physical phenomenon.
-It is used to obtain accurate results about physical quantities.
-It helps in performing experiments for making our daily food easier.
8. Define fundamental and derived quantities with two examples of each.

Ans: Those units which are used to measure the fundamental physical quantities and which do not depend on other units are called fundamental units. For example: Meter, second, kilogram,etc.
Those units which are used to measure the derived physical quantities and which depends on other units are called derived units. For example:Area,Volume, Power,etc.
9. What is the standard unit used to measure the mass?

Ans:The standard unit used to measure the mass is kilogram(kg).
10. The unit of the area is derived unit. Why?

Ans: The unit of area is derived unit because the unit of area can be expressed by multiplying two fundamental units of length i.e, meter. Hence, unit of area is a derived unit.
11. What is the SI unit of current?

Ans: The SI unit of current is Ampere(A).

12. Define: a. length, b. Mass c. Time
a. Length: Length is defined as the the distance between two points.
b. Mass:Mass is defined as the quantity of matter contained in the body.
c. Time: Time is the duration between two events.

13. Write some formula used to calculate the area of a regular object?

Ans: Some formula used to calculate the are of regular objects are:
A= l×b, A = 1/2 b×h, A= l2 etc.
14. Name the fundamental units involved in the unit of force.

Ans: the fundamental units involved in the unit of force are:  Kg, m and s.
15. Distinguish between fundamental and derived unit.

Ans: The differences between fundamental and derived units are:

Fundamental units	Derived units
1. The units of fundamental quantities are called fundamental units	1. The units of derived quantities are called derived units.
2. These units are independent of each other.	2. These units are obtained one or more fundamental units i.e these depend upon each other.
3. Examples: second, kilogram, Kelvin, mole etc.	3. Examples: Joule, watt, Newton etc.

16. Distinguish between mass and weight.
Ans: The differences between mass and weight are: 

S.no	Mass	Weight
1	It is the quantity of matter contained in a body.	It is the amount of force of gravity acted on a body.
2	Mass of an object does not vary from place to place	Weight of an object varies from place to place.
3	Mass is scalar quantity	Wight is the vector quantity.
4	Mass is measured by beam balance.	It is measured by spring balance.
5	There is no place or condition under which mass of an object be zero.	Weight of an object will be zero, at the centere of the earth or at the place where R = 0.
6	The SI unit of mass is kilogram(Kg).	The SI unit of weight is Newton(N).

17. Distinguish between density and relative density.
Ans: The differences between density and relative density are:

Density	Relative density
1. It is the mass per unit volume.	1. It is the ratio of density of a substance to the density of water at 4°C.
2. It can be expressed as: $D=\frac{m}{v}$	2. It can be expressed as: $R.D=\frac{\text{Density of substance}}{\text{density of water at 4}{}^\circ \text{C}}$
3. Its SI unit is kg/ m3.	3. It has no unit.

18. Define: a. 1 Kg                           b. 1 m                    c. 1 s
Ans:
a. One kg: One standard kilogram is the mass of Platinum Iridium cylinder of length equal to height at the international bureau of weights and measures in France. This cylinder is about 4 cm height with a diameter of 4 cm.

b. One meter: One standard metre is the distance between two fine gold lines on Platinum-Iridium rod at 0°C, which is kept at international bureau of weight and measure in France.

c. One second: One standard second is the time taken by 9192631770 vibrations of the radiation emitted by Cesium - 133 atom.

19. What is SI system? Write the differences between SI system and CGS system.
Ans: Scientists all over the world realized the necessity of common system of units for the sake of uniformity and convenience. So, in 1960 AD, the eleventh general conference of scientists held on France recommended a common system of units. It is an extended form of metric system ie. MKS which is called SI system.

CGS system is the French system of measurement. In this system, the unit of length is centimetre(cm), mass is gram(gm) and time is second (s). 

20. What is mass? Write its SI unit.

Ans: It is the quantity of matter contained in a body. It is a scalar constant quantity ie. it does not vary from place to place. It is measured by beam balance. There is no place or condition under which mass of an object be zero. Its SI unit is kilogram (kg).
21. What do you mean by physical quantity?

Ans: The quantity that can be measured directly or indirectly is called physical quantity. Examples: area, density, volume, pressure etc.
22. What is density? Define relative density.

Ans:
Density: 
Density is defined as the mass per unit volume. Its is scalar quantity. Its SI unit is kg / m3. Mathematically,
                                             Density $D=\frac{M}{V}$
Relative density: 
Relative density is defined as the ratio of density of a substance to the density of water at 4°C.
Mathematically,
                                             Relative density \[\text{R}\text{.D}=\frac{\text{Density of substance}}{\text{Density of water at 4 }\!\!{}^\circ\!\!\text{ C}}\]
Relative density has no unit because it the ratio between two densities.

Meaning of Relative Density:

• If a substance has relative density less then 1, it will float in the liquid taken.
• If a substance has relative density equal to 1, it will float with completely immersed in the liquid. 
• If a substance has relative density greater then 1, it will sink in the liquid.  

23. Define: a. FPS system       b. MKS system                  c. SI system                        d. CGS system

Ans:
a. FPS system: It is the British system of unit. In this system, the unit of length, mass and time are foot (ft), pound (lb) and second (s) respectively.

b. MKS system: In this system the units of the length, mass and time are meter (m), kilogram (kg) and second (s) respectively. In our country Nepal, M.K.S system is used as the standard for measuring physical quantities.

c. SI system: Scientists all over the world realized the necessity of common system of units for the sake of uniformity and convenience. So, in 1960 AD, the eleventh general conference of scientists held on France recommended a common system of units. It is an extended form of metric system (MKS). This conference defined various quantities and ready to provide sample of defined quantities to every-nation. Thus, it provides the uniformity on measurement.

d. CGS system: It is the French system of unit. In this system, the unit of length is centimetre (cm) that of mass is gram (gm) and time is second (s).
24. Define a light year. What quantity does it measure?

Ans: Light year is the distance traveled by light in one year. It is used to measure the large distances such as distance between two planets, tow stars etc. One light year equal to 9.46×10^15 meter.
25. Name the instruments that are used for the measurement of volume of liquid.

Ans:The instruments that are used to measure the volume of liquid are measuring cylinder, burette, pipette, volumetric flask etc.
26. How is the volume of an irregular body determined?

Ans:The volume of an irregular body is determined by immersing the irregular object into a  measuring cylinder by water displacement method.
27. Give the derived units of: a. Pressure                             b. Force                                c. power
Ans: The derived units of:
a. Pressure: $\frac{Kg}{m{{s}^{2}}}$
b. Force: $\frac{Kgm}{{{s}^{2}}}$
c. Power: $\frac{Kg{{m}^{2}}}{{{s}^{2}}}$

28. Define SI units. What are the other basic units involved in it?
Ans:Scientists all over the world realized the necessity of common system of units for the sake of uniformity and convenience. So, in 1960 AD, the eleventh general conference of scientists held on France recommended a common system of units. It is an extended form of metric system (MKS).
The other basic units involved in it are: Amount of substance (mol), Electric current (A), Luminous intensity (cd), and Temperature (K).