PHYSICS CLASS 9TH CHAPTER-1 NOTES

CHAPTER-1 PHYSICAL QUANTITIES AND MEASUREMENT

Chapter-1 notes, solved exercise, Do you Know? , Numerical, short questions.

Q-1: What is science? How science and technology related to society? 

SCIENCE: 

“The knowledge gained through observation and experimentation is called Science”. 

Remember That: 

The word science is derived from the Latin word scientia, which means knowledge. 

Science Technology and Society: 

Man has always been inspired by the wonders of nature and remained in search of the truth and reality. He observes various phenomena and tries to find their answers by logical reasoning. 

Not until eighteenth century, various aspect of material objects were studied under a single subject called Natural Philosophy. But as the knowledge increased, it was divided into two main streams: 

Physical Sciences: 

It deals with the study of non-living things. 

Biological Sciences: 

It is concerned with the study of livening things. 

Measurement: 

Measurements are not confined to science they are part of our lives. They play an important role to describe and understand the physical world. Over the centuries, man has improved the methods of measurements. 

Q-2: Define physics? Describe different branches of physics. 

PHYSICS: “Physics is the branch of science that deals with matter, energy and their relationship”. 

BRANCHES OF PHYSICS: 

Physics is divided into the following branches: 

1. Mechanics: 

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

2. Heat: 

It deals with the nature of heat, modes of transfer and effects of heat. 

3. Sound: 

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

4. Light (Optics): 

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

5. Electricity and Magnetism: 

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

6. Atomic Physics: 

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

7. Nuclear Physics: 

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

8. Plasma Physics: 

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

9. Geophysics: 

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

Q-3: What are the types of physical sciences? Define physics also describe importance of physics in daily life. 

TYPES OF PHYSICAL SCIENCES: 

In the nineteenth century, physical sciences were divided into five distinct disciplines: 1. Physics 2. Chemistry 3. Astronomy 4. Geology 5. Meteorology 

The most fundamental of these is physics. The laws and principles of physics help us to understand nature. 

PHYSICS: “Physics is the branch of science that deals with matter, energy and their relationship”. 

Importance of Physics in Daily Life: 

The rapid progress in science during the 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. 

For Example: 

1. Consider the means of transportation such as car and aero-planes is made on the principles of mechanics.

2. Refrigerator is based on the principles of thermodynamics.

3. In our daily life, we hardly find a device where physics is not involved. Consider pulleys that make it easy to lift heavy loads.

4. Electricity is used not only to get light and heat but also mechanical energy that derives fans and electric motors etc.

5. Domestic appliances such as air-conditioners, vacuum cleaners, washing machines and micro ovens etc. are the fruits of hard work of physicist in the field of physics.

6. Similarly the means of communication such as radio, television, telephone and computer are the results of applications of physics. 

Conclusion: 

These devises have made our lives much easier, faster and more comfortable than the past. 

For Example: 

Think of what a mobile phone smaller than our palm can do? It allows us to contact people anywhere in the world and to get latest worldwide information. We can take and save the pictures, send and receive messages of our friends. We can also receive radio transmission and can use it as a calculator as well. 

Drawbacks of Discoveries of Science: 

However, 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. 

Q-4: Define physical quantities? What are its types? 

PHYSICAL QUANTITIES: 

“All measurable quantities are called physical quantities”. 

For Example: 

Such as length, mass, time and temperature etc. 

Explanation: 

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

For Example: 

If the length of a student is 104cm then 104 is its numerical magnitude and centimetre is the unit of measurement. Similarly when a grocer says that each bag contains 5kg sugar, he is describing its numerical magnitude as well as the unit of measurement. It would be meaningless to state 5 or kg only. 

Types of Physical quantities: 

Physical quantities are divided into base quantities and derived quantities. 

Base Quantities: 

“Base quantities are the quantities on the basis of which other quantities are expressed”. 

Explanation: 

There are seven physical quantities which form the foundation for other physical quantities. These physical quantities are called the base quantities. These are length, mass, time, electric current, temperature, intensity of light and the amount of a substance. 

Derived Quantities: 

“The quantities that are expressed in terms of base quantities are derived quantities”. 

Explanation: 

Those physical quantities which are expressed in terms of base quantities are called the derived quantities. These include area, volume, speed, force, work, energy, power, electric charge, electric potential etc. 

Q-5: Define unit? What is international system of units? Also explain base units and derived units? 

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”. 

Explanation: 

Measuring is not simply counting,e.g. If we need milk or sugar, we must also understand how much quantity of milk or sugar we are talking about. Thus there is a need of some standard quantities for measuring or comparing unknown quantities. 

INTERNATIONAL SYSTEM OF UNITS: 

“A worldwide system of measurements is known as international system of units (SI)”. 

Explanation: 

With the developments in the field of science and technology, the need for a commonly acceptable system of units was seriously felt all over the world particularly to exchange scientific and technical information. 

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

Base Units: 

“The units that describe base quantities are called base units”. 

Table: Each base quantity has its SI unit. Table shows seven base quantities, their SI units and theirsymbols. 

Quantity Unit Name Symbol Name Symbol

  • Length L Meter m
  • Mass M Kilogram kg
  • Time T Second s
  • Temperature T Kelvin K
  • Electric current I Ampere A
  • Intensity of light L Candela cd
  • Amount of substance N Mole mol 

Derived Units: 

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

Explanation: 

Derived units are defined in term of base units and are obtained by multiplying or dividing one or more bass units with each other. e.g. The unit of area (meter)2and 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. 

Speed is defined as distance covered in unit time therefore its unit is metre per second. In the same way the unit of density, force, pressure, power etc. can be derived using one or more base units. 

Table: 

Table shows some of derived quantities, their SI units and their 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 kgms–2
  • Pressure P Pascal Pa or Nm–2
  • Density ρ Kilogram per cubic metre kgm–3
  • Charge Q Coulomb C or As 

Q-6: What are prefixes? Explain with examples. 

PREFIXES: 

“The word or letter added before a unit and stand for the multiples or sub-multiples of that unit is known as prefixes”. 

For Example: 

Table shows some multiples and submultiples of prefixes: 

Prefixes Symbol Multiplier:

exa E 1018atto a 10–18
peta P 1015femto f 10–15
tera T 1012pico p 10–12
giga G 109nano n 10–9
mega M 106micro 10–6
kilo k 103milli m 10–3
hecto h 102centi c 10–2
deca da 101deci d 10–1

Explanation: 

Some of the quantities are either very large or very small,e.g. 250,000 mand 0.000,002 g etc. SI units have the advantage that their multiples and sub-multiples can be expressed in terms 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 1000 or 103. Thus 

20,000 g = 20,000 kg = 20 kg 

1000 or 20,000g = 20×103 g = 20 kg 

Let us consider few more examples: 

i. 200000 ms–1 = 200 x 103ms–1 = 200 kms–1 

ii. 4 800 000 W = 4800×103 W = 4800 kW or = 4.8 x 106 = 4.8MW

iii. 3 300 000 000 Hz = 3 300×106 Hz =3300 MHz or = 3.3 x 109 Hz = 3.3GHz

iv. 0.00002 g = 0.02 x 10–3 g = 0.02 mg or = 20 x 10–6 g = 20 μg

v. 0.000 000 0081 m = 0.0081 x 10–6 m = 0.0081 μm or = 8.1 x 10–9 m = 8.1 nm 

Note: 

i. Prefixes are used with both types of units i.e. base and derived units.

ii. Double prefixes are not used,e.g.no prefix is used with kilogram since it already contains the prefix kilo. 

Q-7: What is meant by scientific notation? Explain with examples. 

SCIENTIFIC NOTATION: 

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

Explanation: 

A simple but scientific way to write large or small numbers is to express them in some power of ten. This saves writing down or interpreting large numbers of zeros. 

For Example: 

The Moon is 384000000 m away from the Earth. Distance of the Moon from the Earth can also be expressed as 3.84 x108 m. This form of expressing a number is called the standard form or scientific notation. 

A number 62750 can be expressed as 62.75×103 or 6.275×104 or 0.6275×105. All these are correct. But the number that has one non-zero digit before the decimal, i.e. 6.275×104 preferably be taken as the scientific notation. Similarly the scientific notation of 0.00045 s is 4.5×10–4 

s. Q-8: What are measuring instruments? Explain. 

MEASURING INTRUMENTS: 

“Measuring instruments are used to measure various physical quantities such as length, mass, time, volume, etc”. 

EXPLANATION: 

Measuring instruments used in the past were not so reliable and accurate as we use today. e.g. sundial, water clock and other time measuring devices used around 1300 AD were quite crude. On the other hand, digital clocks and watches used now a-days are highly reliable and accurate. 

Q-9: What is meter rule and measuring tape? What are their functions and least count? 

METRE RULE: 

“A meter rule is a length measuring instrument”. 

Explanation: 

It is commonly used in the laboratories to measure 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). 

Least Count of Meter Rule: 

“One millimeter is the smallest reading that can be taken using a meter rule and is called its least count of meter rule”. 

Precautions While Using Meter Rule: 

While measuring length or distance, eye must be kept vertically above the reading point. The reading becomes doubtful if the eye is pointed either left or right to the reading point. 

MEASURING TAPE: 

“Measuring tapes are used to measure length in metres and centimeters”. 

Explanation: 

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

Q-10: What is Vernier Callipers? Describe construction, least count, zero error and working of Vernier Callipers? 

VERNIER CALLIPERS: 

“An instrument used to measure small lengths such as internal or external diameter or length of a cylinder etc is called VernierCallipers”. 

Construction: 

A VernierCallipers consists of two jaws. One is a fixed jaw with main scale attached to it. Main scale has centimetre and millimetre marks on it. The other jaw is a moveable jaw. It has vernier scale having 10 divisions over it such that each of its division is 0.9 mm. 

Least Count of VernirCallipers: 

“The difference between one small division on main scale division and one vernier scale division is 0.1 mm. It is called least count (LC) of the VernierCallipers”. 

Least count of the VernierCallipers can also be found as given below: 

Least count of vernier calipers=smallest reading on main scale no. of division on vernier scale = 1 mm 10 div = 0.1 mm = 0.01 cm 

Zero Error and Zero Correction: 

To find the zero error, close the jaws of Vernier Calipers gently. If zero line of the vernier scale coincides with the zero of the main scale then the zero error is zero. Zero error will exist if zero line of the vernier scale is not coinciding with the zero of main scale. 

Positive Zero Error: 

Zero error will be positive if zero line of vernier scale is on the right side of the zero of the main scale.

Negative Zero Error: 

Zero error will be negative if zero line of vernier scale is on the left side of zero of the main scale. 

Taking a Reading on Vernier Calliper: 

Let us find the diameter of a solid cylinder using Vernier Callipers.

1. Place the solid cylinder between jaws of the Vernier Callipers. Close the jaws till they press the opposite sides of the object gently.

2. Note the complete divisions of main scale past the vernier scale zero in a tabular form.

3. Next find the vernier scale division that is coinciding with any division on the main scale multiply it by least count of Vernier Callipers

4. Now add main scale reading and vernier scale reading. This is equal to the diameter of the solid cylinder.

5. Add zero correction (Z.C) to get correct measurement.

6. Repeat the above procedure and record at least three observations with the solid cylinder displaced or rotated each time. 

Digital Vernier Callipers: 

Digital vernier callipers has greater precision than mechanical vernier callipers. Least count of digital vernier callipers is 0.01 mm. 

Q-11: What is screw gauge? Describe construction, least count, zero error and working of screw gauge? 

SCREW GAUGE: 

“A screw gauge is an instrument that is used to measure small lengths with accuracy greater than a vernier callipers. It is also called micro meter screw gauge”. 

Construction: 

A simple screw gauge consists of a U-shaped metal frame with metal stud at its one end. A hollow cylinder (or sleeve) has a millimeter scale over it along a line called index line parallel to its axes. The hollow cylinder acts as a nut. It is fixed at the end of U-shaped frame opposite to the stud. 

Pitch of the Screw Gauge: 

A thimble has threaded spindle inside it. As the thimble completes one rotation, the spindle moves 1 mm along the index line. It is because the distance between consecutive threads on the spindle is 1 mm. This distance is called the pitch of screw on the spindle. 

Least Count of Screw Gauge: 

The thimble has 100 divisions around its one end. It is the circular scale of the screw gauge. As thimble completes one rotation, 100 divisions pass the index line and the thimble moves 1 mm along the main scale. Thus each division of circular scale crossing the index line moves the thimble through 1/100 mm or 0.01 mm on the main scale. 

Least count of a screw gauge can also be found as given below: 

  • Least count = Pitch
  • Number divisions on circular scale = 1mm ——- 100 = 0.01 mm = 0.001 cm Thus least count of the screw gauge is 0.01 mm or 0.001 cm. 

Zero Error of Screw Gauge: 

To find the zero error, close the gap between the spindle and the stud of the screw gauge by rotating the ratchet in the clockwise direction. If zero of circular scale coincides with the index line, then the zero error will be zero. 

Positive Zero Error: 

Zero error will be positive if zero of circular scale is behind the index line. In this case, multiply the number of divisions of the circular scale that has no crossed the index line with the least count of screw gauge to find zero error. 

Negative Zero Error: 

Zero error will be negative if zero of circular scale has crossed the index line. In this case, multiply the number of divisions of the circular scale that has crossed the index line with the least count of screw gauge to find the negative zero error. 

Taking a Reading Using a Screw Gauge: 

The diameter of given wire can be found as follows: 

1. Close the gap between the spindle and the stud of the screw gauge by turning the ratchet in clockwise direction.

2. Note main scale as well as circular scale readings to find the error and hence zero correction of the screw gauge.

3. Open the gap between stud and spindle of the screw gauge by turning the ratchet in anti- clockwise direction. Place the given wire in the gap. Turn the ratchet so that the object is pressed gently between studs and the spindle.

4. Note main scale as well as circular scale readings to find the diameter of the given wire.

5. Apply zero correction to get the correct diameter of the wire.

6. Repeat steps 3, 4 and 5 at different places of the wire to obtain its average diameter. 

Q-12: Explain the construction and working of mass measuring instruments? 

MASS MEASURING INSTRUMENTS: 

Pots were used to measure grain in various part of the world in the ancient times. However, balances were also in use by Greeks and Romans. Today people use many types of mechanical and electronic balances. You might have seen electronic balances in sweet and grocery shops. These are more precise than beam balances and are easy to handle. 

1. Beam Balance: 

Beam balances are still in use at many places. In a beam balance, the unknown mass is placed in one pan. It is balanced by putting known masses in the other pan. 

2. Physical Balance: 

A physical balance is used in the laboratory to measure the mass of various objects by comparison. It consists of a beam resting at the centre on a fulcrum.The beam carries scale pans over the hooks on either side. Unknown mass is placed on the left pan. Find some suitable standard masses that cause the pointer to remain at zero on raising the beam. 

Method to Find Mass with Physical Balance: 

Follow the steps to measure the mass of a given object.

i. Adjusting the leveling screws with the help of plumb line to level the platform of physical balance. ii. Raise the beam gently by turning the arresting knob clockwise. Using balancing screws at the ends of its beam, bring the pointer at zero position. iii. Turn the arresting knob to bring the beam back on its supports. Place the given object (stone) on its left pan. iv. Place suitable standard masses from the weight box on the right pan. Raise the beam. Lower the beam if its pointer is not at zero. v. Repeat adding or removing suitable standard masses in the right pan till the pointer rests at zero on raising the beam. vi. Note the standard masses on the right pan. Their sum is the mass of the object on the left pan. 

3. Lever Balance: 

A lever balance consists of a system of levers. When lever is lifted placing the object in one pan and standard masses on the other pan, the pointer of the lever system moves. The pointer is brought to zero by varying standard masses. 

4. Electronic Balance: 

Electronic balances come in various ranges, milligram ranges, gram ranges and kilogramme ranges. Before measuring the mass of a body, it is switched on and its reading is set to zero. Next place the object to be weighed. The reading on the balance gives you the mass of the body placed over it. 

The Most Accurate Balance: 

The mass of one rupee coin is done using different balances as given below: 

a) Beam Balance: 

Let the balance measures coin’s mass = 3.2 g A sensitive beam balance may be able to detect a change as small as of 0.1 g Or 100 mg. 

b) Physical Balance: 

Let the balance measures coin’s mass = 3.24 g Least count of the physical balance may be as small as 0.01 g or 10 mg. Therefore, its measurement would be more precise than a sensitive beam balance. 

c) Electronic Balance: 

Let the balance measures coin’s mass = 3.247 g Least count of an electronic balance is 0.001 g or 1 mg. Therefore, its measurement would be more precise than a sensitive physical balance. 

Conclusion: 

Thus electronic balance is the most sensitive balance in the above balances. 

Q-13: What is stopwatch? Explain the construction and working of stopwatch? 

STOPWATCH: 

 “A stopwatch is used to measure the time interval of an event”. 

Types of Stop Watch: 

There are two types of stopwatches: i. Mechanical stopwatch ii. Digital stopwatch 

i. Mechanical Stopwatch: 

A mechanical stopwatch can measure a time interval up to a minimum 0.1 second. 

How to Use a Mechanical Stopwatch: 

A mechanical stopwatch has a knob that is used to wind the spring that powers the watch. It can also be used as a start-stop and reset button. The watch starts when the knob is pressed once. When pressed second time, it stops the watch while the third press brings the needle back to zero position. 

ii. Digital Stopwatch: 

Digital stopwatches commonly used in laboratories can measure a time interval as small as 1/100 second or 0.01 second. 

How to Use a Digital Stopwatch: 

The digital stopwatch starts to indicate the time lapsed as the start/stop button is pressed. As soon as start/stop button is pressed again, it stops and indicates the time interval recorded by it between start and stop of an event. A reset button restores its initial zero setting. 

Q-14: What is measuring cylinder? Explain the construction and working of measuring cylinder? 

MEASURING CYLINDER: 

“Measuring cylinder is used to measure the volume of a liquid or powdered substance. It is also used to find the volume of an irregular shaped solid insoluble in a liquid by displacement method”. 

Construction: 

A measuring cylinder is a glass or transparent plastic cylinder. It has a scale along its length that indicates the volume in milliliter (mL). Measuring cylinders have different capacities from 100 mL to 2500 mL. 

How to Use a Measuring Cylinder: 

Take a measuring cylinder. Place it vertically on the table. Pour some water into it. Note that the surface of water is curved. The meniscus of the most liquids curve downwards while the meniscus of mercury curves upwards. 

Precautions While Using Measuring Cylinder: 

While using a measuring cylinder, it must be kept vertical on a plane surface.The correct method to note the level of a liquid in the cylinder is to keep the eye at the same level as the meniscus of the liquid. It is incorrect to note the liquid level keeping the eye above the level of liquid. When the eye is above the liquid level, the meniscus appears higher on the scale. Similarly when the eye is below the liquid level, the meniscus appears lower than actual height of the liquid. 

Measuring Volume of an Irregular Shaped Solid: 

Measuring cylinder can be used to find the volume of a small irregular shaped solid that sinks in water. Let us find the volume of a small stone. Take some water in a graduated measuring cylinder. Note the volume Vi of water in the cylinder. Tie the solid with a thread. Lower the solid into the cylinder till it is fully immersed in water. Note the volume Vf of water and the solid. Volume of the solid will be Vf – Vi. 

Q-15: What is meant by significant figure? What are the main points to be kept in mind while determining the significant figures of a measurement? Also explain the rules of rounding the number? 

SIGNIFICANT FIGURES: 

“All the accurately known digits and the first doubtful digit in an expression are called significant figures”.

Explanation: 

The value of a physical quantity is expressed by a number followed by some suitable unit. Every measurement of a quantity is an attempt to find its true value. The accuracy in measuring a physical quantity depends upon various factors: 

➢ the quality of the measuring instrument ➢ the skill of the observer ➢ the number of observations made 

For Example: 

A student measures the length of a book as 18 cm using a measuring tape. The numbers ‘of significant figures in his/her measured value are two. The left digit 1 is the accurately known digit. While the digit 8 is the doubtful digit for which the student may not be sure. 

Another student measures the same book using a ruler and claims its length to be 18.4 cm. In this case all the three figures are significant. The two left digits 1 and 8 are accurately known digits. Next digit 4 is the doubtful digit for which the student may not be sure. 

A third student records the length of the book as 18.425 cm. interestingly, the measurement is made using the same ruler. The numbers of significant figures is again three, consisting of two accurately known digits 1, 8 and the first doubtful digit 4. The digits 2 and 5 are not significant. It is because the reading of these last digits cannot be justified using a ruler. Measurement upto third or even second decimal place is beyond the limit of the measuring instrument. 

An improvement in the quality of measurement by using better instrument increases the significant figures in the measured result. The significant figures are all the digits that are known accurately and the one estimated digit. More significant figure means greater precision. 

Rules to Find the Significant Digits in a Measurement: 

The following rules are helpful in identifying significant figure: 

i. Non-zero digits are always significant e.g. 27 has 2 significant digits and 275 has 3 significant digits. ii. Zeros between two significant figures are also significant e.g. 2705 has 4 significant digits. iii. Final or ending zeros on the right in decimal fraction are significant e.g.275.00 has 5 significant digits. iv. Zeros written on the left side of the decimal point for the purpose of spacing the decimal point are not significant e.g. 0.03 has 1 significant digit and 0.027 has 2 significant digits. v. In whole numbers that end in one or more zeros without a decimal point. These zeros may or may not be significant. In such cases, it is not clear which zeros serve to locate the position value and which are actually parts of the measurement. In such case, express the quantity using scientific notation to find the significant zero e.g. 123000 in scientific notation it can be written as 1.23 x 105has 3 significant digits. 

Rounding the Numbers: 

1. lf the last digit is less than 5 then it is simply dropped. This decreases the number of significant digits in the figure e.g. 1.943 is rounded to 1.94 (3 significant figure) 2. If the last digit is greater than 5, then the digit on its left is increased by one. This also decreases the number of significant digits in the figure e.g. 1.47 is rounded to digits 1.5 (2 significant figure) 3. If the last digit is 5, then it is rounded to get nearest even number e.g. 1.35 is rounded to 1.4 and 1.45 is also rounded to 1.4. 

Q-16: What are laboratory safety rules and what are the laboratory safety equipments? 

LABORATORY SAFETY RULES: 

The students should know what to do in case of an accident. The charts or posters are to be displayed in the laboratory to handle situations arising from any mishap or accident. For your own safety and for the safety of others in the laboratory, follow safety rules given below: 

1. Do not carry out any experiment without the permission of your teacher. 2. Do not eat, drink, play or run in the laboratory. 3. Read the instructions carefully to familiarize yourself with the possible hazards before handling equipment and materials. 4. Handle equipment and materials with care. 5. Do not hesitate to consult your teacher in case of any doubt. 6. Do not temper with the electrical appliances and other fittings in the laboratory. 7. Report any accident or injuries immediately to your teacher. 

LABORATORY SAFETY EQUIPMENTS: 

A school laboratory must have safety equipments such as: 1. Waste-disposal basket 2. Fire extinguisher 3. Fire alarm 4. First Aid Box 5. Sand and water buckets 6. Fire blanket to put off fire 7. Substances and equipments that need extra care must bear proper warning signs such as given in figure. 

PHYSICS CLASS 9TH CHAPTER-1 NOTES

QUICK QUIZ

QUICK QUIZ QUICK QUIZ 1.1: 

1. Why do we study physics?

Ans: We study physics to understand the physical phenomena happening around us. 

2. Name five branches of physics? 

Name of five branches of physics are i. Mechanics ii. Heat iii. Sound iv. Nuclear physics v. Atomic physics 

QUICK QUIZ 1.2: 

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

Base Quantities Derived Quantities Base quantities are the quantities on the The quantities that are expressed in basis of which other quantities are terms of base quantities are derived expressed. quantities. There are seven base quantities. These There are more than seven derived are length, mass, time, electric current, quantities. These include area, volume, temperature, intensity of light and the speed, force, work, energy, power, amount of a substance. electric charge, electric potential etc.

2. Identify the base quantities in the following: 

a) Speed b) Area c) Force d) Distance 

Ans: Here distance is the base quantity. 

3. Identify the following as base or derived quantity: 

Density, force, mass, speed, time, length, temperature and volume Ans: 

Base Quantities Derived Quantities: Mass Density Time Force Length Speed Temperature Volume 

QUICK QUIZ 1.3: 

1. Name five prefixes most commonly used. Ans: 

Prefixes Symbol Multiplier: mega M 106 kilo k 103 centi c 10–2 milli m 10–3 micro 10–6 

2. The Sun is one hundred and fifty million kilometers away from the Earth. Write this a) As an ordinary whole number b) In scientific notation 

Ans: a) As an ordinary whole number: 150 x 106 km as 1 million = 106 150 x 106 x 103 m 1 kilo = 103 150 x 109 m 150,000,000,000 m

b) In scientific notation: 150,000,000,000 m = 1.5 x 1011 m

3. Write the numbers given below in scientific notation? 

a) 3000000000 ms–1 b) 6400000 m c) 0.0000000016 g d) 0.0000548 s Ans: 

Numbers Scientific Notation 3000000000 ms–1 3 x 109ms–1 6400000 m 6.4 x 106 m 0.0000000016 g 1.6 x10–9g 0.0000548 s 5.48 x10–5

QUICK QUIZ 1.4: 

1. What is the least count of vernier callipers?

Ans: The least count of vernier callipers is 0.1 mm or 0.01 cm. 

2. What is the range of vernier callipers used in your physics laboratory?

Ans: The range of vernier callipers used in physics laboratory is from 0.01cm to 12 cm. 

3. How many divisions are there on its vernier scale?

Ans: Vernier scale has 10 divisions over it such that each of its division is 0.9 mm. 

4. Why do we use zero correction?

Ans: To apply zero is known as zero correction. Zero correction is applied to get accurate result. 

PHYSICS CLASS 9TH CHAPTER-1 NOTES

MINI EXERCISE

MINI EXERCISE MINI EXERCISE 1.1: 

1. Express 1 cm3 in millilitres?

Ans: Volume is a derived quantity. As 1 L = 1000 mL Then 1 L = 1 dm= (10 cm)3 = 1000 cm3 1 cm3 = 1 mL

2. Express 1 m3 in litres?

Ans: As 1 L = 1000 cm= 1000 100 x 100 x 100 m3 1 L= 1 1000 m3 1 m3 =1000 L 

MINI EXERCISE 1.2: 

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

1. What is the range of your paper scale?

Ans: The range of my paper scale is from 0.5 cm to 30 cm. 

2. What is its least count?

Ans: The least count of my paper scale is 0.5 cm. 

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

Ans: The measurement of pencil measured by paper scale is 5.5 cm while the measurement of pencil measured by meter ruler is 5.2 cm. 

The measurement of pencil measured by the meter ruler is more accurate because it even can measure the length in millimetres. 

MINI EXERCISE 1.3: 

1. What is the least count of screw gauge?

Ans: The least count of screw gauge is 0.01 mm or 0.001 cm. 

2. What is the pitch of your laboratory screw gauge?

Ans: The pitch of laboratory screw gauge is 1 mm. 

3. What is the range of school laboratory screw gauge?

Ans: The range of laboratory screw gauge is 0.01 mm to 100 mm. 

4. Which one of the two instruments is more precise and why? a) Vernier callipers b) Screw gauge 

Ans: The instrument screw gauge is more precise than verniercallipers because the least count of vernier callipers is 0.01 cm while the least count of screw gauge is 0.001 cm. 

MINI EXERCISE 1.4: 

1. What is the function of balancing screws in a physical balance?

Ans: Balancing screws in a physical balance is used to bring the pointer at zero position. 

2. On what pan we place the object?

Ans: We place the object to be measured in the left pan and the varying weights or masses in the right pan. It is due to the reason that we feel convenience to change weights with our right hand when required.

 PHYSICS CLASS 9TH CHAPTER-1 NOTES

DO YOU KNOW

1. What is saying of Lord Kelvin about measurements?

Ans: 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 meager and of unsatisfactory kind. 

2. What is Andromeda?

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

3. How can we produce pollution free electricity?

Ans: Wind turbines are used to produce pollution free electricity. 

4. What is the function of Hubble Telescope?

Ans: Hubble Space Telescope orbits around the earth. It provides information about stars. 

5. Which one of the instruments is more precise and why? a) meter ruler b) Vernier callipers c) Screw gauge

Ans: Least count of ruler is 1 mm. It is 0.1 mm for vernier callipers and 0.01 mm for screw gauge. Thus measurements taken by micrometer screw gauge are the most precise than the other two. 

6. What do you know about more precise balance?

Ans: The precision of a balance in measuring mass of an object is different for different balances. e.g. a sensitive balance cannot measure large masses. Similarly a balance that measures large masses cannot be sensitive. 

Some digital balances measure even smaller difference of the order of 0.0001 g or 0.1 mg. such balances are considered the most precise balance. 

PHYSICS CLASS 9TH CHAPTER-1 NOTES

MULTIPLE CHOICE QUESTIONS

MULTIPLE CHOICE EXERCISE 

Q-1.1: Multiple Choice Questions: 

1. The number of base units in SI are …………………….. a) 3 b) 6 c) 7 d)

2. Which one of the following unit is not a derived unit? a) pascal b) kilogram c) newton d) watt 

3. Amount of substance in terms of numbers is measured in ……………………… a) gram b) kilogramme c) newton d) mole 

4. An interval of 200 s is equivalent to …………………. a) 0.2 s b) 0.02 s c) 2 x 10–4 s d)2 x 10–6

5. Which one of the following is the smallest quantity? a) 0.01 g b) 2 mg c) 100 μg d) 5000 ng 

6. Which instrument is most suitable to measure the internal diameter of a test tube? a) metre rule b) verniercallipers c) measuring tape d) screw gauge 

7. A student claims the diameter of a wire as 1.032 cm using verniercallipers. Upto what extent do you agree with it? 

a) 1 cm b) 1.0 cm c) 1.03 cm d) 1.032 cm 

8. A measuring cylinder is used to measure ……………….. a) mass b) area c) volume d) level of a liquid 

9. A student noted the thickness of a glass sheet using a screw gauge. On the main scale, it reads 3 divisions while 8th division on the circular scale coincides with index line. It thickness is …………………… a) 3.8 cm b) 3.08 mm c) 3.8 mm d)3.08 m 

10. Significant figures in an expression are ………………… a) all the digits b) all the accurately known digits c) all the accurately known digits and the first doubtful digit d) all the accurately known digits and all the doubtful digits 

MCQS ANSWERS 1 2 3 4 5 6 7 8 9 10 c b d c d b c c b c 

PHYSICS CLASS 9TH CHAPTER-1 NOTES

REMAINING EXERCISE 

Q-1.2: What is the difference between base quantities and derived quantities? Give three examples in each case.

Base Quantities Derived Quantities: Base quantities are the quantities on the The quantities that are expressed in basis of which other quantities are terms of base quantities are derived expressed. quantities. There are seven base quantities. These There are more than seven derived are length, mass, time, electric current, quantities. These include area, volume, temperature, intensity of light and the speed, force, work, energy, power, amount of a substance. electric charge, electric potential etc. 

Q-1.3: Pick out the base units in the following: joule, newton, kilograms, hertz, mole, ampere, meter, Kelvin, coulomb and watt.

Ans: Here Kilogram, mole, ampere, meter, and Kelvin are the base units. 

Q-1.4: Find the base quantities involved in each of the following derived quantities? a) speed b) volume c) force d) work

Ans: a) Speed: The formula of speed is Speed = DISTANCE time Unit of speed = unit of distance  unit of time = m s = ms–1

Conclusion: 

Unit of speed shows that speed is derived quantity and it is derived from base quantities length and time. Moreover unit of length is mere and unit of time is second. 

b) Volume: The formula of volume of cube is Volume = length x width x height Unit of volume = unit of length x unit of width x unit of height = m x m x m = m3

Conclusion: Unit of volume shows that volume is derived quantity and it is derived from base quantity length. Moreover unit of length is meter. 

c) Force: The formula of force is Force = mass x acceleration 

Unit of force = unit of mass x unit of acceleration = kg x ms–2 = kgms–2 = N

Conclusion: Unit of force shows that force is derived quantity and it is derived from base quantities mass, length and time. Moreover unit of mass is kilogram unit of length is mere and unit of time is second. 

d) Work: The formula of work is Work = force x distance 

Unit of work = unit of force x unit of distance = kgms–2 x m = kgm2s–2 = J

Conclusion: Unit of work shows that work is derived quantity and it is derived from base quantities mass, length and time. Moreover unit of mass is kilograms unit of length is meter and unit of time is second. 

Q-1.5: Estimate your age in seconds?

Ans: Suppose age of person = 14 years 

Since Total days in one year = 365 Total hours in one day = 24 hours Total minutes in one hour = 60 min Total seconds in minutes = 60 sec Therefore, Age of person in seconds = 14 x 365 x 24 x 60 x 60 = 441,504,000 sec 

Q-1.6: What role SI units have played in the development of science? 

Ans: The SI units have brought consistency and uniformity in measurements, calculations. SI is very helpful to exchange scientific and technical information at the international level. It has also facility to convert one unit into other. 

Q-1.7: What is meant by vernier constant?

Ans: Least count of vernier callipers is also called vernier constant. 

“The difference between one small division on main scale division and one vernier scale division is 0.1 mm. It is called least count (LC) or vernier constant of the VernierCallipers”. 

Least count or vernier constant of the Vernier Callipers can also be found as given below: 

Least count of vernier calipers =smallest reading on main scale no. of division on vernier scale 1mm 10 div = 0.1 mm = 0.01 cm 

Q-1.8: What do you understand by the zero error of measuring instrument?

Ans: Zero error is basically the systematic error which exists in the measuring instrument. This is the error in instrument due to which it shows measurement more than actual measurement or less than actual measurement. This error can be recovered by adding or subtracting from the observed measurement. 

Q-1.9: Why is the use of zero error necessary in measuring instruments?

Ans: Zero error is necessary in measuring instrument to obtain an extreme correct value. 

Q-1.10: What is a stopwatch? What is the least count of a mechanical stopwatch you have used in the laboratories?

Ans: STOPWATCH: “A stopwatch is used to measure the time interval of an event”. A mechanical stopwatch can measure a time interval up to a minimum 0.1 second. 

Q-1.11: Why do we need to measure extremely small interval of times? Ans: We need to measure extremely small interval of times for greater accuracy in obtaining results. 

For Example: Time period of simple pendulum and in free fall experiments time taken in falling the bob etc, these time intervals must be measured with perfect accuracy. 

Q-1.12: What is meant by significant figures of measurement? Ans: SIGNIFICANT FIGURES: 

“All the accurately known digits and the first doubtful digit in an expression are called significant figures”. 

For Example: i. 0.055 has 2 significant digits ii.2.907 has 4 significant digits. 

Q-1.13: How is precision related to the significant figures in a measured quantity?

Ans: More significant means more precision. Thus a measured quantity having more significant figures will be more precise or accurate. 

For Example: If length of rod is measured using ruler and it is 5 cm. When the same length is measured by using vernier callipers it becomes 5.02 cm. In first case significant figure is 1 while in the second case it becomes 3. Since second measurement is more precise because the number of significant figures are increased. Hence greater number of significant figures means greater precision. 

 

EXAMPLES

Example 1.1: Find the diameter of a cylinder placed between the outer jaws of vernier callipers as shown in figure: 

Sol: Zero Correction: 

On closing the jaws of vernier callipers, the position of vernier scale as shown in fig is Vernier division coinciding with main scale = 7 div Zero error (Z.E) = 7 x 0.01 cm = +0.07 cm Zero correction (Z.C) = – 0.07 cm 

Diameter of the Cylinder: Main scale reading Vernier division coinciding with main scale Vernier Scale reading Observed diameter of the cylinder Correct diameter of the cylinder = 2.2 cm = 6 div = 6 x 0.01 cm = 0.06 cm = 2.2 cm + 0.06 cm = 2.26 cm = 2.26 – 0.07 = 2.19 cm Thus the correct diameter of the given cylinder as found by vernier calipers is 2.19 cm. 

Example 1.2: Find the diameter of a wire using screw gauge as shown in figure: 

Sol: Zero Correction: 

On closing the gap of the screw gauge, the position of circular scale is 

Circular division coinciding with index line Zero error (Z.E) 

Zero correction (Z.C) = 24 div = 24 x 0.01 mm = +0.24 mm = –0.24 mm = 1 mm = 85 div = 85 x 0.01 mm = 0.85 mm = 1 mm + 0.85 mm = 1.85 mm = 1.85 – 0.24 = 1.61 mm Thus the correct diameter of the given wire as found by screw gauge is 1.61 mm. 

Example 1.3: Find the mass of a small stone by a physical balance. 

Sol: Follow the steps to measure the mass of a given object. 

i. Adjusting the leveling screws with the help of plumb line to level the platform of physical balance. ii. Raise the beam gently by turning the arresting knob clockwise. Using balancing screws at the ends of its beam, bring the pointer at zero position. iii. Turn the arresting knob to bring the beam back on its supports. Place the given object (stone) on its left pan. iv. Place suitable standard masses from the weight box on the right pan. Raise the beam. Lower the beam if its pointer is not at zero. v. Repeat adding or removing suitable standard masses in the right pan till the pointer rests at zero on raising the beam. vi. Note the standard masses on the right pan. Their sum is the mass of the object on the left pan. 

Example 1.4: Find the number of significant figures in each of the following values. Also express them in scientific notations. 

a) 100.8s b) 0.00580 km c) 210.0 g 

Sol: a) All the four digits are significant. The zeros between the two significant figures 1 and 8 are significant. To write the quantity in scientific notation, we move the decimal point two places to the left, thus 100.8s = 1.008 x102

b) The first two zeros are not significant. They are used to space the decimal point. The digit 5, 8 and the final zero are significant. Thus there are three significant figures. In scientific notation, it can be written as 5.80×10–3 km. 

c) The final zero is significant since it comes after the decimal point. The zero between last zero and 1 is also significant because it comes between the significant figures. Thus the number of significant figures in this case is four. In scientific notation, it can be written as 210.0 g = 2.100 x 102g. Main scale reading Circular division coinciding with index line Circular Scale reading Observed diameter of the wire Correct diameter of the cylinder.

PROBLEMS 

Problem Sol: a)5000 a) b) c)52 d) 1.1: 5000 2000 225 x 10g Express x g 000 –10 10–8 b) kg W s the 2000 following = = = = = 000 5 2 5.2 5.2 2.25 W x x 1010x x quantities x 10 1036c) 10W g 1 x 2 – 1052 x 10 10–10 = = x + –8 5 2 using 103 x kg MW g s 

–10 10= 35.2 prefixes. kg

d) 225 x 10–8 s x 10–6g = 5.2 μg (as (as 10103 6 = = k) M) 

(as 10–6= μ) 

= 2.25 x 102 – 8 s = 2.25 x 10–6s = 2.25 μs (as 10–6= μ) 

Problem 1.2: How do the prefixes micro, nano and pico relate to each other? Sol: As we know 

μ = n = p = Relation of micro with nano: 

1010–6 –9 

10–12 

One n = = = Relation of micro with pico: One p = = = Relation of nano with pico: One p = = = 

10–9 10–3 x 10–6 10–3 μ 

10–12 1010–6 –6 x μ 

10–6 

10–12 10–3 x 10–9 10–3 n Problem 1.3: Your hair grows at the rate of 1 mm per day. Find their growth rate in nms–1. Sol: Given data: 

Growth rate = 1 mm/day Required: 

Growth rate in nms–1= ? As we know 

1 milli 1 nano = = m n = = 1010–3 –9 

In one day = 24 x 60 x 60 = 86400sec Now: 

Growth rate in m/day 

Growth rate in nm/day 

Growth rate in nm/sec 

= 1 x 10–3m/day 1 x 10–3 = 10–9 nm/day 

= 1 1 x x 10106 6 nm/day = nm/sec 

= 0.00001157 x 106 = 11.57 nm/sec 

Problem a) 1168 1.4: Rewrite x 10–27 the b) following 32 x 105 in standard c) 725 x 10form. 

–5d) 0.02 x 10–8 Sol: a) 1168 x 10–27 = 1168 x 10–27 + 3 = 1.168 x 10–24 

b) c) 32 725 x x 10105 –5 = = 32 725 x x 10105 –5 + 1 + 2 = = 7.25 3.2 x x 1010

–3 

d) 0.02 x 10–8 = 0.02 x 10–8 – 2 = 2 x 10–10 

Problem Sol: a) a) b) c) 1.5: 6400 6400 380 300 Write 000 000 km km km 000 the b) msfollowing 380 –1 000 km = =3.8 = quantities 6.4 3 x x 10x 10108 5 msc) 3 km km in –1 300 standard 000 000 form. 

ms–1 d) seconds in a day 

d) seconds in a day = 24 x 60 x 60 s = 86400 s = 8.64 x 104

Problem to its main 1.6: scale On closing such that the 4th jaws division of a Vernier of its vernier callipers, scale zero coincides of the vernier with one scale of the is on main the scale right 

division. Find its zero error and zero correction. Sol: Vernier division coinciding with main scale = 4 div 

Least count of vernier calipers = 0.01 cm Now Zero error (Z.E) = 4 x 0.01 cm 

= +0.04 cm Zero correction (Z.C) = – 0.04 cm 

Problem 1.7: A screw gauge has 50 divisions on its circular scale. The pitch of the screw gauge is 0.5 mm. What is its least count? Sol: No of divisions on circular scale = 50 div 

Pitch of Screw Gauge = 0.5 mm Least count of a screw gauge can be found as given below: 

Least count =

Pitch Number divisionson circular scale 0.5 mm 50 = 0.01 mm = 0.001 cm Thus least count of the screw gauge is 0.01 mm or 0.001 cm. 

Problem 1.8: Which of the following a) 3.0066 m b) 0.00309 kg quantities c) 5.05 have x 10three –27 kg significant d) figures? 

301.0 s Sol: a) 3.0066 m 

The significant figures in this quantity are five. Because the zeros between significant figures are also significant. 

b) 0.00309 kg The significant figures in this quantity are three. Because the zeros used for spacing the decimal point are not significant. 

c) 5.05 x 10–27 kg The significant figures in this quantity are three. Because the zeros between significant figures are also significant. 

d) 301.0 s The significant figures in this quantity are four. Because the zeros after decimal are also significant. 

Hence (b) and (c) have three numbers of significant figures. 

Problem 1.9: What are the significant a) 1.009 mb) 0.00450 kg figures c) 1.66 d) 2001 s in the x 10 following –27 kg measurements? 

Sol: a) 1.009 m The significant figures in this quantity are four. Because the zeros between significant figures are also significant. 

b) 0.00450 kg The significant figures in this quantity are three. Because the zeros used for spacing the decimal point are not significant. 

c) 1.66 x 10–27 kg The significant figures in this quantity are three. Because all the digits before the power of 10 are significant. 

d) 2001 s The significant figures in this quantity are four. Because the zeros between significant figures are also significant. 

Problem 1.10: A chocolate wrapper is 6.7 cm long and 5.4 cm wide. Calculate its area upto reasonable number of significant figures. Sol: Length= 6.7 cm 

Width Area = 5.4 cm = ? Now 

Area = Length x Width 

= 6.7 x 5.4 = 36.18 cm2 = 36 cm2 

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