Physics 9th - Unit 1 - Notes - Physical Quantities and Measurement

 Physical Quantities and Measurement

Notes

  

Q1. Define Science?

Ans: Science:

The knowledge gained through observations and experimentations is called Science. The word science is derived from the Latin word Scientia, which means knowledge. Not until the eighteenth century, various aspect of material objects was studied under a single subject called natural philosophy.

 

 

Q2. Describe the division of science into two main streams?

Ans: Division of science:

As knowledge increased, it was divided into two main streams.

• Physical sciences:

Physical sciences – which deal with the study of non-living things.

• Biological: sciences:

Biological sciences – which are concerned with the study of living things.

 

 

 

Q3. Define Physics?

Ans :  Physics is that branch of science which deals with the study of properties of matter-energy and their mutual relationship.

Q4. Describe the different branches of physics?

Ans: Branches of physics:

• Mechanics:

         It is the study of the motion of objects, its causes and effects.

• Heat:

Deals with the nature of heat modes of transfer and effects of heat.

 iii.   Sound:

It deals with, the physical aspects of sound waves, their production, properties and applications.

• Light (Optics):

It is the study of physical aspects of light, its properties, working and use of optical instruments.

• Electricity and Magnetism:

It is the study of the charges at rest and in motion, their effects and their relationship with magnetism.

• Atomic Physics:

It is the study of the structure and properties of atoms.

• Nuclear Physics:

It deals with the properties and behaviour of nuclei and the particles within the nuclei.

 viii. Plasma Physics:

It is the study of production, properties of the ionic state of matter – the fourth state of matter.

• Geophysics:

 It is the study of the internal structure of the Earth.

 

 

 

Q5. Describe the Lord Kelvin statement?

Ans: Kelvin statement:

When you can measure what you are speaking about and express it in numbers, you know something about it. When you cannot measure what you are speaking about or you cannot express it in numbers, your knowledge is of a meagre and an unsatisfactory kind.

 

 

FOR YOUR INFORMATION

Andromeda:

Andromeda is one of the billions of galaxies of the known universe.

Q6. Describe the crucial role of physics in science, technology and society?

Ans: Crucial role of physics in science, technology and society:

The rapid progress in science during recent years has become possible due to the discoveries and inventions in the field of Physics. The technologies are the applications of scientific principles. Most of the technologies of our modern ° society throughout the world are related to Physics.

Examples:

1. A car is made on the principles of mechanics and a refrigerator is based on the principles of thermodynamics.
2. Consider pulleys that make it easy to lift heavy loads.
3. Electricity is used not only to get light and heat but also mechanical energy that drives fans and electric motors etc.
4. Consider the means of transportation such as car and aeroplanes; domestic

appliances such as air-conditioners, refrigerators, vacuum cleaners, washing, machines, and microwave ovens etc.

5. Similarly, the means of communication such as radio, TV, telephone and computer are the result of applications of Physics. These devices have made out lives much easier, faster and more comfortable than the past.
6. A mobile phone allows us to contact people anywhere in the world and to get the latest worldwide information. We can take and save pictures, send and receive messages from our friends. We can also receive radio transmission and can use it as e calculator as well.

 

 

 

 Q7. List the harmful effects of the scientific inventions on nature?

Ans: The scientific inventions have also caused harms and destruction of serious nature. One of which is the environmental pollution and the other is the deadly weapons.

 

 

DO YOU KNOW?

 

Wind turbines are used to produce pollution-free electricity.

 

Quick Quiz

 

1. Why do we study physics?

Ans:   We study physics because Physics is the branch of science which deals with the matter, energy and their interaction. Most of the technologies of our modern society throughout the world are related to physics.

 

 

 

2. Name any five branches of physics?

 Ans: i. Mechanics

      ii. Thermodynamics

iii. Electromagnetism

iv. Atomic Physics

       v. Plasma Physics

 

 

 

Q8. Explain with examples that science is based on physical quantities which consist of numerical magnitude and a unit.

 Ans: Physical Quantities:

All measurable quantities are called physical quantities such as length, mass, time and temperature.

A physical quantity possesses at least two characteristics in common. One is its numerical magnitude and the other is the unit in which it is measured.

Examples:

For example, if the length of a student is 104 cm then 104 is its numerical magnitude and centimetre is the unit of measurement.

Similarly, when a grocer says that each bag contains 5 kg sugar, he is describing its numerical magnitude as well as the unit of measurement. It would be meaningless to state 5 or kg only.

Physical quantities are divided into base quantities and derived quantities.

 

 

 

Q9. What is the difference between base quantities and derived quantities? Give three examples in each case.

Ans: See Q # 1.2 from Exercise.

 

 

 

Q10. Define unit?

 Ans: Unit:

Once a. standard is set for a quantity then it can be expressed in terms of that standard quantity. This standard quantity is called a unit.

Q11. List the seven units of System International (SI) along with their symbols and physical quantities?

 Ans: An international system of units:

The eleventh General Conference on Weight and Measures held in Paris in 1960 adopted a world-wide system of measurements called the International System of Units. The International System of Units is commonly referred to as SI.

Base units:

The units that describe base quantities are called base units. Each base quantity has its SI unit. The table shows seven base quantities, their SI units and their symbols.

 

                  Base quantities, their SI units with symbols quantity Unit Name Symbols

Quantity		Unit
Name	Symbol	Name	Symbol
Length	|	meter	m
Mass	M	kilogram	kg
Time	T	second	s
Electric current	I	ampere	A
Intensity of light	L	candela	cd
Temperature	T	kelvin	K
Amount of a substance	N	mole	mol

• Q12. What are the main advantages of system international (SI units)?

                                             OR

   Why do we prefer SI units?

  Ans: i. SI system is in use all over the world.

  1. Manipulation in this system is quite easy i.e. the multiple and sub multiple of different units are obtained simply by multiplying or dividing with ten or powers of tens.

   

   

   

  Q13.  Explain with examples the derived units?

  Ans:   Derived units:

  The units used to measure derived quantities are called derived units.

  Derived units are defined in terms of base units and are obtained by multiplying or dividing one, or more base units with each other.

   Examples:

  1. The unit of area (meter)2 and the unit of volume (meter)3 are based on the unit of length, which is meter. Thus, the unit of length is the base unit while the unit of area and volume are derived units.
  2. Speed is defined as the distance covered in unit time; therefore, its unit is meter per second. In the same way, the unit of density, force, pressure, power etc. can be derived using one or more base units.

   

  Derived quantities and their SI units with symbols

  Quantity		Unit
  Name	Symbol	Name	Symbol
  Speed	V	meter per second	ms-1
  Acceleration	A	meter per second per second	ms-2
  Volume	V	cubic meter	m3
  Force	F	newton	N or (kg m s2)
  Pressure	P	pascal	Pa or (N m-2)
  Density	Ρ	kilogram per cubic meter	Kgm-3
  Charge	Q	coulomb	C or (As)

   

  Quick Quiz

   

  1. How can you differentiate between the base and derived quantities?

   Ans: Difference between the base and derived quantities:

   

  Base Quantities	Derived Quantities
  i.    Base quantities are the quantities based on which other quantities are expressed.	i. The quantities that are expressed in terms of base quantities are called derived quantities
  ii. Length, mass, time, electric current, temperature, the intensity of light | and the amount of a substance.	ii. Area, volume, speed, force, work, energy, power, electric charge, electric potential, etc.

  2. Identify the base quantity is the following:

  • Speed (ii) Area (iii)          Force (iv)           Distance

  Ans:   i.   The distance can be considered as base quantity because the distance is equal tothe length and its unit is meter.

  1.    Speed, area and force are derived quantities because these quantities are express in terms of base quantities.
  2. Identify the following as base or derived quantity: density, force, mass, speed, time, length, temperature and volume.

  Ans:

  Base Quantities	Derived Quantities
  Length, mass, time, temperature.	Density, volume, speed, force,

   

  Mini Exercise

  Volume is a derived quantity

  1L        = 1000mL

  1L       = 1 dm3

  = (10cm) 3

  = 1000 cm3

  1mL = 1 cm3

  Express 1 m3 in liters    ……… L

  Solution: -1m3 in liters=1000L

   

   

   

  Q14. Define prefixes. Interconvert the prefixes and their symbols to indicate multiples and sub-multiples for both bases and derived units?

   Ans: Prefixes:

  Prefixes are the words or letters added before Si units such as kilo, mega, giga and milli.

  SI units have the advantage that their multiples and sub-multiples can be expressed in terms of prefixes. These prefixes are given in Table.

  Some Prefixes

  Prefix	Symbol	Multiplier
  exa	E	1018
  peta	P	1015
  tera	T	1012
  giga	G	109
  mega	M	106
  Kilo	K	103
  hecto	h	102
  deca	da	101
  deci	d	10-1
  centi	c	10-2
  milli	m	10-3
  micro	M	10-6
  nano	n	10-9
  Pico	P	10-12
  femto	f	10-15
  atto	a	10-18

   

  Advantages of prefixes:

  The prefixes are useful to express very large or small quantities. For example, divide 20,000 g by 1000 to express it into kilogram, since kilo represents 103 or 1000.

  Thus 20,000g = 20,000 ÷ 1,000Kg  = 20kg

  or    20,000 g     = 20 x 10g             = 20kg

  Note:

  Double prefixes are not used. For example, no prefix is used with kilogram since it already contains the prefix kilo.

  Prefixes given in Table are used with both types of base and derived units.

  Multiples and sub-multiples of length:

  1km	103m
  1cm	102m
  1mm	10-3m
  1µm	10-6m
  1nm	10-9m

   

   

   

  Q15. What do you understand by scientific notation?

  Ans: Scientific notation/Standard form:

  In scientific notation, a number is expressed as some power of ten multiplied by a number between 1 and 10.

   Examples:

  3. The Moon is 384000000 meters away from the Earth. The distance of the moon from the Earth can also be expressed as 3.84 x 108 This saves writing down or interpreting large numbers of zeros.
  4. A number 62750 can be expressed as 6.275 x 104. Similarly, the standard form of 0.00045 is 4.5 x 10-4

   

   

  Quick Quiz

   

  1. Name five prefixes most commonly used.

  Ans:     (1) kilo (k) = 103      (2) centi(c)10-2        (3) milli(m) = 10-3

  (4) micro (u) = 10-6        (5) mega (M) = 106

   

   

   

  2. The Sun is one hundred and fifty million kilometres away from the Earth. Write this.

  • as an ordinary whole number

  • in scientific notation.

  Ans:    The distance of Sun from the Earth = 150 million km

  • as an ordinary whole number:

  = 150 x 106km= 150 x 106 x 103m                                         1 million 106 1 kilo = 103

                  = 150000000000 m

  • In scientific notation.

  = 150 x 106 x 103

  = 150 x 109

  = 15 x 10 x 109

  = 15 x 1010

  = 15 ÷ 10 x 10 x 1010

  =1.5 x 1011

  =1.5 x 1011 m

  3. Write the numbers given below in scientific notation.
  4. 3000000000 ms-1 (c) 6400000 m
  5. 0000000016 g (d) 0.0000548 s

  Ans:

  • 3000000000 ms-1

  = 3 x 1000000000 ms-1

  = 3x 109 ms-1

   

  • 6400000 m

  = 64 x 105m

  = 6.4 x 10 x 105

  = 6.4 x 106m

   

  • 0000000016 g

  = 0.0000000016 ÷ 10000000000 g

  = 16 x 10-10g

  =1.6x 10x 10-10g

  =1.6×10-9g

   

  • (d)  0.0000548 s

  = 0.0000548

  =    0.0000548 ÷10000000

  =    548 x 10-7

  = 5.48 x 102 x 10-7

  =5.48x 10-5 s

   

   

  FOR YOUR INFORMATION

   

  Hubble Space Telescope:

  Hubble Space Telescope orbits around the Earth. It provides information about stars.

   

   

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  Q16. What is the meter rule? What is the least count of a meter rule used in the laboratories?

   Ans: The meter rule:

  A meter rule is a length measuring instrument as shown in the figure. It is commonly used in the laboratories to measure the length of an object or distance between two points. It is one meter long which is equal to 100 centimeters. Each centimeter (cm) is divided into 10 small divisions called millimeter (mm). Thus, one millimeter is the smallest reading that can be taken using a meter rule and is called its least count.

  Least count of meter rule = 0.1 cm or 1mm

   

   

   

  Q17. What is a measuring tape? What is the least count of a measuring tape?

  Ans: The measuring tape:

  Measuring tapes are used to measure the length in meters and centimeters. A measuring tape used by blacksmith and carpenters. A measuring tape consists of a thin and long strip of cotton, metal or plastic generally 10 m, 20 m, 50 m or 100 m long. Measuring tapes are marked in centimeters as well as in inches.

  Least count of measuring tape = 0.1 cm or 1 mm

   

  Mini Exercise

   

  Cut a strip of a paper sheet. Fold it along its length. Now mark centimeters and half a centimeter along its length using a ruler. Answer the following questions:

  1. What is the range of your paper scale?

  Ans: The range of the paper scale is 20 cm.

   

   

   

  2. What is its least count?

  Ans: The least count of paper scale is 1 cm.

   

   

   

  3. Measure the length of a pencil using you. Paper scale and with a meter ruler. Which one is more accurate and why?

  Ans: The measurement of pencil measured by the meter ruler is 4.2 cm. The measurement of pencil measured by the ruler is more accurate because it even can measure the length in millimeters.