# Physics 9th Class Complete Important Question For Examination Preparation

Physics 9th Class Complete Important Question for Examination Preparation

NOTES OF PHYSICS FOR X SCIENCE

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CHAPTER NO 2

MEASUREMENT

Meter

Meter is the unit of length in S.I.system.

Meter is defined as “The distance between the two marks on a Platinum-Iridium bar kept at 0 C in the International Bureau of Weight and Measures in Paris.”

One meter = 100 cm

One meter = 1000 mm

Kilogram

Kilogram is the unit of mass in S.I.system.

“Kilogram is defined as the mass of a platinum cylinder placed in the International Bureau of Weight and Measures in Paris.”

One kilogram = 1000gram

Second

Second is the unit of time in S.I.system.

A second is defined in terms of the time period of Cs-133 atoms.

i.e.” one second is equal to 9,192,631,770 periods of vibrations of Cs-133 atoms.”

60 seconds = one minute

3600 seconds = one hour

Least Count

Minimum measurement that can be made by a measuring device is known as ” LEAST COUNT .”

Least count (vernier callipers) = minimum measurement on main scale / total number of divisions on vernier scale

Least count (screw gauge) = minimum measurement on main scale / total number of divisions on circular scale

Smaller is the magnitude of least count of a measuring instrument, more precise the measuring instrument is.

A measuring instrument can not measure any thing whose dimensions are less than the magnitude of least count.

Least Count of Vernier Callipers = 0.01 cm

Least Count of Micrometer Screw gauge = 00.01 cm

Zero Error

It is a defect in a measuring device (Vernier Callipers & Screw Gauge).

When jaws of a Vernier Callipers or Screw Gauge are closed, zero of main scale must coincides with the zero of vernier scale or circular scale in case of screw gauge.

If they do not coincide then it is said that a zero error is present in the instrument.

Types Of Zero Error

Zero error may be positive or negative.

A positive zero error in the instrument shows a larger measurement than the actual measurement.

In order to get exact measurement, positive zero error is subtracted from the total reading.

.

A negaive zero error in the instrument shows a smaller measurement than the actual measurement.

In order to get exact measurement, negative zero error is addd to the total reading.

Pitch

“Perpendicular distance between two consecutive threads

of the screw gauge or spherometer is called PITCH.”

Pitch = Distance travelled on main scale / total number of rotations

Error

An error is defined as

“The difference between the measured value and actual value.”

If two persons use the same instrument for measurement for finding the same measurement, it is not essential that they may get the same results.There may arises a difference between their measurements.This difference is referred to as an “ERROR”.

Types Of Error

Errors can be divided into three categories:

(1) Personal Error

(2) Systematic Error

(3) Random Error

Personal Error

An error comes into play because of faulty procedure adopted by by the observer is called “PERSONAL ERROR”.

Personal error comes into existence due to making an error in reading a scale.It is due to faulty procedure adopted by the person making measurement.

Systematic Error

The type of error arises due to defect in the measuring device is known as “SYSTEMATIC ERROR”

.Generally it is called “ZERO ERROR”. it may be positive or negative error. Systematic error can be removed by correcting measurement device.

Random Error

The error produced due to sudden change in experimental conditions is called “RANDOM ERROR”.

For example:

During sudden change in temperature, change in humidity, fluctuation in potential difference(voltage).

It is an accidental error and is beyond the control of the person making measurement.

CHAPTER NO 5

FORCE & MOTION

FORCE

“Force is that agent which changes or tends to change the state of rest or of uniform motion of a body.”

In the light of Newton’s 2nd law of motion Force may be defined as :

“Force acting on a body is equal to the product of the mass and acceleration produced in the body.”

i.e.

F = ma

Force can accelerate or decelerate a body.

Force is a vector quantity.

UNITS OF FORCE

(i) NEWTON (N) in S.I system

(ii) DYNE in C.G.S system

(iii) POUND (Lb) in BRITISH ENGINEERING SYSTEM (F.P.S)

NEWTON

Newton is the unit of force and can be defined as:

“The amount of force that produces an acceleration of 1 m/s2

in a body of mass 1-kg is equal to 1 NEWTON.”

1 N = 1 kg x 1m/s2

[ N = kg m/s2]

NEWTON ‘S FIRST LAW OF MOTION

STATEMENT:

Newton ‘s first law of motion states that

“Every body remains at rest or continues to move with uniform

velocity in straight line unless an unbalanced force acts upon it”.

EXPLANATION

First law of motion consists of two parts:

PART NO 1:

The first part states that a body at rest remains at rest unless an unbalanced force acts upon it.

This part is in accordance with our common experience for example, a book lying on a table remains at rest unless it is lifted or pushed by an external force.

PART NO 2 :

Second part states that a body in motion remains in motion with uniform velocity unless an unbalance force acts upon it. This part is not self-evident because a ball pushed once does not continue its motion forever. A little consideration however, shows that there is an opposing force like ground friction and air friction acting in this case. These frictional forces are responsible to stop the ball. If we eliminate these opposing forces, a body in motion will continue its motion forever.

INERTIA

“Tendency of a body by virtue of which the body at rest or

moving with uniform velocity retains its state is called INERTIA.”

OR

“Property of a body by which a body resists a force, applied on it to change its state is called INERTIA.”

INERTIA of a body is directly related to its mass. Heavy bodies have greater inertia while lighter bodies have little inertia.

LAW OF INERTIA AND THE

FIRST LAW OF MOTION

Every body in the universe opposes the force which tends to change its state of rest or of uniform motion. This property INERTIA is a direct consequence of FIRST LAW OF MOTION. As heavy bodies due to greater INERTIA requires forces of large magnitude and bodies of small masses require small forces.

By the above explanation of INERTIA we conclude that the state of rest or motion does not change by its self unless an external force acts upon it, which is according to the FIRST LAW OF MOTION.

Thus the FIRST LAW OF MOTION is also called LAW OF INERTIA.

CHAPTER NO 6

STATICS

Statics

Static deals with the bodies at rest under number of forces, the equilibrium and condition of equilibrium etc.

Equilibrium

A body is said to be in equilibrium if it is at rest or moving with uniform velocity.

In other words if the linear and angular acceleration of a body are zero, the body is said to be in equilibrium.

Or we can say that when two or more forces act on a body such that their resultant or combining effect on the body is Zero and the body retains its state of rest or of uniform motion then the body is said to be in equilibrium.

Example

Book lies on a table, suspended bodies, all stationary bodies , jump by using parachute.

Types of equilibrium

With respect to the state of a body, equilibrium may be divided into two categories:

1. Static equilibrium.

2. Dynamic equilibrium.

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Static equilibrium

If the combined effect of all the forces acting on a body is zero and the body is in the state of rest then its equilibrium is termed as static equilibrium.

For example:All stationary bodies

Dynamic equilibrium

when a body is in state of uniform motion and the resultant of all forces acting upon it is zero then it is said to be in dynamic equilibrium.

For example: Jump by using parachute.

Conditions of equilibrium

There are two conditions of equilibrium are as follows

First condition of equilibrium

The first condition of equilibrium stated as follow:

To maintain the transitional equilibrium in a body the algebraic sum of all the forces acting on the body is equal to zero

i.e. .

In other words we can say that to maintain equilibrium the sum of all the forces acting along X-axis is zero and the sum of all the forces acting along Y-axis is zero.

i.e.

&

Second condition of equilibrium

The second condition of equilibrium stated as follow:

A body will be in rotational equilibrium when the algebraic sum of clock wise torque and anti clock wise torque is zero.

In other words:

A body will be in rotational equilibrium if vector sum of all the torques acting on the body is zero.

CHAPTER NO 7

CIRCULAR MOTION AND GRAVITATION

GRAVITATION

Every object in our universe attracts the other object with certain fore towards its center. This force of attraction is known as GRAVITATIONAL FORCE and the phenomenon is called GRAVITATION. This is gravitational force which is responsible for the uniformity or regularity in our daily astronomical life. The whole system of the universe is in order only due to this force. Due to gravitation, the system of our universe is working uniformly and smoothly.The planets around the earth or around the sun moves in an orderly motion due to gravitation.

NEWTON?S LAW OF GRAVITATION

In order to explain the gravitational force between two bodies, Newton formulated a fundamental law known after his name i.e. “NEWTON’S LAW OF GRAVITATION”

Newton?s law of gravitation states that every object in the universe attracts the other object with a force and :

(1) The gravitational force of attraction between two bodies is directly proportional to the product of their masses.

F a m1 x m2 ——- (1)

(2) The gravitational force of attraction between two bodies is inversely proportional to the square of the distance between their centers.

F a 1/d2 ——— (2)

MATHEMATICAL REPRESENTATION

Combining (1) and (2)

F a m1m2 /d2

F = G m1m2/d2

Where G = universal gravitational constant

Value of G:

G = 6.67 x 10-11 Nm2/kg2

MASS OF THE EARTH

Consider a body of mass ?m? placed on the surface of the earth. Let the mass of the earth is ?Me? and radius of earth is ?Re? .