Physics Project On Physical World, Units and Measurement

MADE BY-
SAMIRAN GHOSH
CLASS- XI “A”

Science is a systematic enterprise
that builds and
organizes knowledge in the form of
testable explanations and
predictions about the universe. In
an older and closely related
meaning, "science" also refers to a
body of knowledge itself, of the
type that can be rationally
explained and reliably applied. A
practitioner of science is known as
a scientist.

- Investigations in physics
generally follow the
scientific method
-Observations + initial data
collection leading to a
question, hypothesis
formulation and testing,
interpret results + revise
hypothesis if necessary,
state conclusions
-Some hypotheses can
be tested by making
observations.
-Others can be tested by
building a model and
relating it to real-life
situations.

- A way of describing the physical world
- Physics is understanding the behavior and structure of
matter
- It deals with how and why matter and energy act as
they do
-Physics comes from the Greek “physis” meaning “nature”
and the
Latin “physica” meaning natural things
- Energy is the conceptual system for explaining how the
universe works and accounting for changes in matter
- Although energy is not a “thing” three ideas about energy are
important
1. It is changed from one form to another (transformed) by
physical events
2. It cannot be created nor destroyed (conservation)
3. When it is transformed some of it usually goes into heat

One large question about scientific theories that excites
philosophical and scientific attention concerns the possibility
of producing a single theory that will encompass the domains
of all the sciences.
Many thinkers are attracted by the idea of a unified science,
or by the view that the sciences form a hierarchy. Chemical
reactions themselves involve the forming and breaking of
bonds, and these are matters of microphysics. A complete
account of those ultimate constituents and their interactions
would thus amount to a “theory of everything.”
Reductionism is a philosophical position which holds that a
complex system is nothing but the sum of its parts, and that
an account of it can be reduced to accounts of individual
constituents. This can be said of objects, phenomena,
explanation, theories, and meanings.

Branch
in
PHYSICS
Thermodynamics
– Heat and
temperature
Mechanics
–Motion and its
causes
Vibrations and
Waves – Periodic
motion
Atomic –
Structure of the
atom, energy
associated with
atomic changes
Nuclear –
Structure of the
nucleus, energy
associated with
nuclear changes
Electromagnetism
– Electricity,
magnetism and
EM waves
Optics – Behavior
of light

Physics - the study of matter, energy and their
interactions - is an international enterprise, which
plays a key role in the future progress of humankind.
The support of physics education and research in all
countries is important because:
1) Physics is an exciting intellectual adventure that
inspires young people and expands the frontiers of
our knowledge about Nature.
2) Physics generates fundamental knowledge needed
for the future technological advances that will
continue to drive the economic engines of the world.
3) Physics contributes to the technological
infrastructure and provides trained personnel
needed to take advantage of scientific advances and
discoveries.

4) Physics is an important element in the education of
chemists, engineers and computer scientists, as well
as practitioners of the other physical and biomedical
sciences.
5) Physics extends and enhances our understanding of
other disciplines, such as the earth, agricultural,
chemical, biological, and environmental sciences, plus
astrophysics and cosmology - subjects of substantial
importance to all peoples of the world.
6) Physics improves our quality of life by providing the
basic understanding necessary for developing new
instrumentation and techniques for medical
applications, such as computer tomography, magnetic
resonance imaging, positron emission tomography,
ultrasonic imaging, and laser surgery.

The Strong Force
A force which can hold a nucleus together against
the enormous forces of repulsion of the protons is
strong indeed. However, it is not an inverse square
force like the electromagnetic force and it has a
very short range. Yukawa modeled the strong force
as an exchange force in which the exchange particles
are pions and other heavier particles. The range of a
particle exchange force is limited by the uncertainty
principle. It is the strongest of the four
fundamental forces.

One of the four fundamental forces, the electromagnetic
force manifests itself through the forces between charges
(Coulomb's Law) and the magnetic force, both of which are
summarized in the Lorentz force law. Fundamentally, both
magnetic and electric forces are manifestations of
an exchange force involving the exchange of photons. The
quantum approach to the electromagnetic force is
called quantum electrodynamics or QED. The electromagnetic
force is a force of infinite range which obeys the inverse
square law, and is of the same form as the gravity force.
The Electromagnetic Force

The Weak Force
One of the four fundamental forces, the weak
interaction involves the exchange of the intermediate
vector bosons, the W and the Z. Since the mass of
these particles is on the order of 80 GeV, the
uncertainty principle dictates a range of about 10-
18 meters which is about .1% of the diameter of a
proton. The weak interaction changes
one flavor of quark into another. For example, in
the neutron decay depicted by the Feynman diagram at
left above, one down quark is changed to an up quark,
transforming the neutron into a proton.

The Gravitational Force
It is the force of mutual attraction between two
bodies by the virtue of their masses. Related by-
It is a universal attractive force. It obeys inverse
square law. It is the weakest force in nature. It is
conservative, central and long range force. It is
caused due to the exchange of particle called
Graviton.
2
21
r
mm
GF 


Law Of Conservation Of Energy
 Conservation of energy implies that energy can be
neither created nor destroyed, although it can be
changed from one form (mechanical, kinetic, chemical,
etc.) into another. In an isolated system the sum of all
forms of energy therefore remains constant. For
example, a falling body has a constant amount of
energy, but the form of the energy changes from
potential to kinetic. According to the theory
of relativity, energy and mass are equivalent. Thus,
the rest mass of a body may be considered a form of
potential energy, part of which can be converted into
other forms of energy.

Law Of Conservation Of
Linear Momentum
 Conservation of linear momentum expresses the fact that a
body or system of bodies in motion retains its total
momentum, the product of mass and vector velocity, unless
an external force is applied to it. In an isolated system
(such as the universe), there are no external forces, so
momentum is always conserved. Because momentum is
conserved, its components in any direction will also be
conserved. Application of the law of conservation of
momentum is important in the solution of collision
problems. The operation of rockets exemplifies the
conservation of momentum: the increased forward
momentum of the rocket is equal but opposite in sign to the
momentum of the ejected exhaust gases.

Law Of Conservation Of
Angular Momentum
 Conservation of angular momentum of rotating
bodies is analogous to the conservation of linear
momentum. Angular momentum is a vector
quantity whose conservation expresses the law
that a body or system that is rotating continues
to rotate at the same rate unless a twisting force,
called a torque, is applied to it. The angular
momentum of each bit of matter consists of the
product of its mass, its distance from the axis of
rotation, and the component of its velocity
perpendicular to the line from the axis.

Law of Conservation of mass
 Conservation of mass implies that matter can be
neither created nor destroyed—i.e., processes
that change the physical or chemical properties of
substances within an isolated system (such as
conversion of a liquid to a gas) leave the total
mass unchanged. Strictly speaking, mass is not a
conserved quantity. However, except in nuclear
reactions, the conversion of rest mass into other
forms of mass-energy is so small that, to a high
degree of precision, rest mass may be thought of
as conserved.

Law Of Conservation Of Charge
 Conservation of charge states that the total
amount of electric charge in a system does not
change with time. At a subatomic level, charged
particles can be created, but always in pairs with
equal positive and negative charge so that the
total amount of charge always remains constant.
 In particle physics, other conservation laws apply
to certain properties of nuclear particles, such
as baryon number, lepton number, and
strangeness. Such laws apply in addition to those
of mass, energy, and momentum encountered in
everyday life and may be thought of as analogous
to the conservation of electric charge.

Fundamental units
The physical quantities which can be treated as
independent of other physical and are not usually defined
in terms of other physical quantities are called physical
quantities. Such as-
STANDARD
MEASURES

Quantity Unit Symbol
Length meter m
Mass kilogram kg
Temperature kelvin K
Time second s
Amount of
Substance
mole mol
Luminous Intensity candela cd
Electric Current ampere a

Derived units
The physical quantities whose defining operations are based
on other physical quantities are called as derived units. Such
as-
 speed (v) = distance / time * unit: m/s
acceleration (a) = velocity / time * unit: m/s/s = m/s2
force (F) = mass x acceleration *unit: kgm/s2
energy (E) = force x distance *unit: kgm2/s2 = Nm=J
charge (Q) = current x time *unit: As = C

SYSTEM OF UNITS
I. cgs system- Set up in France. It is based on
centimeter, gram and second as the fundamental
units of length, mass and time respectively.
II. fps system- It is a British system based on foot,
pound and second as the fundamental units of
length, mass and time respectively.

III.mks system- It is also a French system based on
meter, kilogram and second as the fundamental
units of length, mass and time respectively.
IV. SI: The international system of units- It is a
metric system of units consisting of seven base
quantities – length, mass, time, electric current,
thermodynamic temperature, amount of
substance, and luminous intensity and two
supplementary units- plane angle and solid
angle

Advantages of SI
1. SI is a coherent system of units i.e system
based on a certain set of fundamental units,
from which all derived units are obtained by
multiplication or division without introducing
numerical factors.
2. SI is a rational system of units as it assigns only
one unit to be a particular physical quantity. For
example, joule is the unit for all types of energy.
This is not so in other systems of units.

3. SI is an absolute system of units. There are
no gravitational units on the system. This use
factor ‘g’ is thus eliminated.
4. SI is a metric system i.e the multiples and
sub multiples of units are expressed as
power of 10.
5. In current electricity, the absolute units on
the SI, like ampere for current, volt for
potential difference, ohm for resistance,
Henry for inductance, farad for capacity and
so on.

1. Meter (m)
2. Second (s)
3. Kilogram (kg)
4. Kelvin (K)
5. Ampere (A)
6. Candela (cd)
7. Mole (mol) = 6.02 x 1023

Unit of length (meter)
 The meter is the length of the path travelled by
light in vacuum during a time interval of 1/299
792 458 of a second.
 The 1889 definition of the meter, based on the
international prototype of platinum-iridium, was
replaced by the 11th CGPM (1960) using a
definition based on the wavelength of krypton 86
radiation. This change was adopted in order to
improve the accuracy.

Unit of mass (kilogram)
 The kilogram is the unit of mass; it is equal to
the mass of the international prototype of the
kilogram.
 The international prototype of the kilogram,
an artifact made of platinum-iridium, is kept
at the BIPM under the conditions specified by
the 1st CGPM in 1889 (CR, 34-38) when it
sanctioned the prototype and declared:
 This prototype shall henceforth be considered
to be the unit of mass.

Unit of time (second)
 The second is the duration of 9 192 631 770
periods of the radiation corresponding to the
transition between the two hyperfine levels of
the ground state of the cesium 133 atom.
 The unit of time, the second, was at one time
considered to be the fraction 1/86 400
 of the mean solar day. The exact definition of
“mean solar day” was left to the
 astronomers. However measurements showed that
irregularities in the rotation of the
 Earth made this an unsatisfactory definition

Unit of electric current
(ampere)
 The ampere is that constant current which, if
maintained in two straight parallel conductors
of infinite length, of negligible circular cross-
section, and placed 1 meter apart in vacuum,
would produce between these conductors a
force equal to 2 × 10−7 newton per meter of
length.

Unit of thermodynamic
temperature (kelvin)
 The kelvin, unit of thermodynamic temperature, is
the fraction 1/273.16 of the thermodynamic
temperature of the triple point of water.
 Because of the manner in which temperature
scales used to be defined, it remains common
practice to express a thermodynamic
temperature, symbol T, in terms of its difference
from the reference temperature T0 = 273.15 K,
the ice point.

Unit of amount of substance
(mole)
1. The mole is the amount of substance of a
system which contains as many elementary
entities as there are atoms in 0.012 kilogram of
carbon 12; its symbol is “mol.”
2. When the mole is used, the elementary
entities must be specified and may be atoms,
molecules, ions, electrons, other particles, or
specified groups of such particles.

Unit of luminous intensity
(candela)
 The candela is the luminous intensity, in a given
direction, of a source that emits monochromatic
radiation of frequency 540 × 1012 hertz and that
has a radiant intensity in that direction of 1/683
watt per steradian.
 It follows that the spectral luminous efficacy for
monochromatic radiation of frequency of 540 ×
1012 hertz is exactly 683 lumens per watt,
K(λ555) = 683 lm/W = 683 cd sr/W (the
wavelength λ of radiation of this frequency is
about 555 nm).

Determination of Diameter of Moon
 Let moon be the astronomical object of
diameter D. Let E be the point on earth's
surface. A telescope is focused on
moon's surface and its image is observed
as shown in figure is measured. S is the
distance between moon and the Earth's
surface.
 The diameter AB of moon is considered
as a circular arc of radius S.
 Diameter of the moon can be found by
knowing q and S.
 This above formula holds good only if S
is very large and D can be considered as
a small arc of radius S.

Determination of distance of moon from
earth (by parallax method)
 Let the object O be viewed with
our eyes which is at a distance of r,
making an angle between the two
eyes as shown in the diagram.
 The angle q, caused by the two
lines drawn from the position of
the two eyes to the object, is
called angle of parallax.
 If we can consider OA and OB as
radius of a circle and the distance
x (AB) as arc of the circle, then we
have.

 However, if we consider O, referred in the
above diagram to be the moon or a nearby
star, then the angle q is too small in the
view of the large astronomical distance and
the place of observation. Hence, in order to
have a better and valid point of observation,
two points on the surface of the Earth is
taken as the basis for observation instead
of the two eyes. In order to have
simultaneous observation of the moon, we
select a very distant star at O and measure
the angle between O and the two points on
the Earth, as shown in the diagram below

To Determine the Height of an Electric Pole
 Let AB be an electric pole, standing
upright, on the ground. Let the point C
be the observation point i.e., the
observer standing. Therefore, BC is a
horizontal distance on the ground and
angle is subtended between the base
and the top of the electric pole. The
point C is also called as the elevation of
the electric pole and the distance from
BC to the point between the point of
observation and the foot of the electric
pole is x and 'h' is one height of the
electric pole.

 i.e., h = x tan q, where the values of x
and q could be known and the height of the
electric pole be determined. This method is
called Triangulation method.

To Determine the Height using a Sextant
 AB and CD are two mirrors
fixed, as in the diagram, parallel
to each other and facing each
other, i.e., the reflection on CD
is seen on AB. A small telescope
and a vernier travelling over a
scale, graduated in degrees,
constitute the sextant.
 The sextant is fixed firmly to
view the horizon, when the
reading on the scale is zero, i.e.,
the reading when the horizon is
seen through both the mirrors.

 The arm of the sextant is a
rotated until the reflected
image of the sun is seen while
the horizon is still seen
directly, as in figure.
 Then, the angle between the
horizontal and CE is twice the
angle through which the arm is
rotated. Since the graduations
on the scale is double the angle
through which the arm is
rotated, the direct setting
gives the reading straightaway.

To Determine the Height of an
Inaccessible Mountain
 Let PQ be the symbolic representation of the mountain
(h), inaccessible for direct measurement. Let A and B be
two points of elevation subtending angles q1 and q2 of the
top of the mountain at P. Since the distance AB is a
known quantity, - a horizontal entity say x, applying
trigonometry, we have,

 where the values of x, q1 and q2 are known as h is
evaluated.

To Measure the Distance of a Submarine
(Echo Method)
 Ultrasonic waves are transmitted through the ocean and
if on its path any submerged objects are encountered,
then as per law, the waves are reflected back to the
origin. The time of sending the wave and the time of
receiving the reflected wave are worked out and the
distance of the submerged object (submarine in this
case) is worked out by the formula
 where s is the distance between the point
of transmission, v is the velocity of sound waves sent
and t is the total time taken by the waves to travel to
and fro.

 The dimensions of a physical quantity are the
powers to which the fundamental quantities are
raised to represent that physical quantity.
 The equation which expresses a physical quantity
in terms of the fundamental units of mass, length
and time, is called dimensional equation.
 According to this principle of homogeneity a
physical equation will be dimensionally correct if
the dimensions of all the terms in the all the
terms occurring on both sides of the equation are
the same.

Main uses of the dimensional analysis
 There are three main uses of the dimensional
analysis-
 (a) To convert a unit of given physical quantities
from one system of units to another system for
which we use
n2 = n1[M1/M2]a[L1/L2]b[T1/T2]c
 (b) To check the correctness of a given physical
relation.
 (c) To derive a relationship between different
physical quantities.

Advantages of Dimensional Analysis
 Dimensional equations are used to validate the
correctness of a physical equation.
 Dimensional equations are used to derive correct
relationship between different physical
quantities.
 Dimensional equations are used to convert one
system of units to another.
 Dimensional equations are used to find the
dimension of a physical constant.

Limitations of Dimensional Analysis
 Dimensional analysis has no information on dimensionless
constants.
 If a quantity is dependent on trigonometric or exponential
functions, this method cannot be used.
 In some cases, it is difficult to guess the factors while
deriving the relation connecting two or more physical
quantities.
 This method cannot be used in an equation containing two or
more variables with same dimensions.
 It cannot be used if the physical quantity is dependent on
more than three unknown variables.
 This method cannot be used if the physical quantity contains
more than one term, say sum or difference of two terms.

For counting of the significant
figure rule are as:
All non- zero digits are significant figure.
All zero between two non-zero digits are significant figure.
All zeros to the right of a non-zero digit but to the left of
an understood decimal point are not significant. But such
zeros are significant if they come from a measurement.
All zeros to the right of a non-zero digit but to the left of
a decimal point are significant.
All zeros to the right of a decimal point are significant.
All zeros to the right of a decimal point but to the left of
a non-zero digit are not significant. Single zero
conventionally placed to the left of the decimal point is not
significant.
The number of significant figures does not depend on the
system of units.

ACCURACY
The accuracy of a measurement is
its relation to the true, nominal, or
accepted value. It is sometimes
expressed as a percentage deviation
from the known value. The known or
true value is often based upon
reproducible measurements.
PRECISSION
A measure of how close a series of
measurements are to one another. A
measure of how exact a
measurement is.

Example:
• Accurate
• Not
Precise
• Not
Accurate
• Precise
• Accurate
and
• Precise

Random Error
 Any factors that randomly affect
measurement of the variable across the
sample.
 For instance, each person’s mood can inflate
or deflate performance on any occasion.
 Random error adds variability to the data but
does not affect average performance for the
group.

Systematic Error
 Any factors that systematically affect
measurement of the variable across the sample.
 Systematic error = bias.
 For instance, asking questions that start “do you
agree with right-wing fascists that...” will tend
to yield a systematic lower agreement rate.
 Systematic error does affect average
performance for the group.

Absolute Error:
 Mean of n measurements
 Absolute error ( Δa ) = amean - a1
 Absolute error is simply the amount of physical error in a
measurement.
 Absolute error is positive , negative or zero.
In plain English: The absolute error is the difference between
the measured value and the actual value. (The absolute error
will have the same unit label as the measured quantity.)

Relative Error:
 Relative error is the ratio of the absolute error
of the measurement to the accepted
measurement. The relative error expresses the
"relative size of the error" of the measurement in
relation to the measurement itself.
 When the accepted or true measurement isknown,
the relative error is found using
which is considered to be a measure of accuracy.

Percentage Error
 It is the relative error measured in percentage.
So,
Percentage Error =
mean absolute value/mean value X 100
=Δamean/amX100

 The relative error expressed in percent is called
percentage error.
 The error is communicated in different
mathematical operations as detailed below:

1 . 1KWH is unit of
1.Time 2. Power
3. Energy 4. Stress
Ans- 3. Energy
2. Unit of Intensity of magnetic induction field is
1.N/Am 2. Tesla
3.Wb/m2 4. All above
Ans- 4. All above

3. Which of the following has no units?
1. Thermal capacity 2. Magnetic
susceptibility
3. Angular acceleration 4. Moment of a magnet
Ans-2. Magnetic susceptibility
4.Which one of the following units is a fundamental
unit?
1. watt 2. joule/sec
3. ampere 4. newton
Ans- 3. ampere

5. kg m/sec is the unit of
1. Impulse 2. Angular acceleration
3 . Capacity of condenser 4. Acceleration.
Ans- Impulse
6. Which of the following is a common unit of a
physical quantity in M.K.S & S.I systems.
1. ampere 2.kelvin
3. mole 4. joule/sec
Ans- 4. joule/sec

7. Which of the following is Unit of length?
1.Lunar Month 2. Kelvin
3. candela 4. Light year
Ans- 4. Light year
8. rad / sec is the unit of
1.Angular displacement 2. Angular velocity
3. Angular acceleration 4. Angular momentum
Ans- 3. Angular acceleration

9. Which of the following is not a unit of power .
1. Watt 2. joule/hr
3. Nm/sec 4.N/sec
Ans- 4.N/sec
10. If the unit of force were 20N,that of power
were 1MW and that of time were 1 millisecond then
the unit of length would be
a) 20m b)50m
c) 100m d) 1000m
Ans-b)50m

11. The physical quantity having units of mass is
1.Density 2.Momentum
3. Inertia 4. Moment of force
Ans- 3. Inertia
12.A force 100N acts on a body.If the units of mass
and length are doubled and unit of time is
halved,then the force in the new system changes to
a)160N b) 1.6 N
c) 16N d) 1600N
Ans-d) 1600N

13. The electric resistance of a conductor is 54
ohm. If the unit of mass and length are tripled,
units of time and electric current are doubled .Then
the value of new electric resistance.
a)540 ohm b) 1080 ohm
c) 1620 ohm d)1944 ohm
Ans-d)1944 ohm
14.Which of the following is a derived unit ?
1. ampere 2. mole
3. candela 4. newton
Ans-4. newton

15) The power of a motor is 150W.If the unit of
force is doubled, unit of velocity is tripled what will
be the new unit of power.
a) 600W b)750W
c) 900W d) 300w
Ans- c) 900W
16. The fundamental unit which is common in F.P.S
and M.K.S systems is
1. foot 2. sec
3.kilo gram 4. pound
Ans- 2. sec

Physics Project On Physical World, Units and Measurement

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