Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

1|Page

Physics Notes Class 11 CHAPTER 2 UNITS
AND MEASUREMENTS
The comparison of any physical quantity with its standard unit is called measurement
...

Units



A definite amount of a physical quantity is taken as its standard unit
...


Fundamental Units
Those physical quantities which are independent to each other are called fundamental
quantities and their units are called fundamental units
...
No
...

Length
metre
2
...

Time
second
4
...
It measures plane angle and
solid angle respectively
...
No
...
ncerthelp
...

e
...
, velocity, acceleration, force, work etc
...

1
...
It is mass of 5
...

2
...
73 wavelength of orange-red light
of Kr-86
...
1 second 1 second is the time in which cesium atom vibrates 9192631770 times in an
atomic clock
...
1 kelvin 1 kelvin is the (1/273
...

5
...

6
...

7
...
012 kg of carbon isotope 6C12
...
The common system of units which is used in mechanics are given below:
1
...

2
...

3
...

4
...

Relationship between Some Mechanical SI Unit and Commonly Used Units
S
...
Physical Quantity
1

Length

2

Mass

Unit
(a) 1 micrometre = 10-6 m
(b) 1 angstrom =10-10 m
(a) 1 metric ton = 103 kg

www
...
com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)

3|Page

(b) 1 pound = 0
...
66 x10-23 kg
Volume
1 litre = 10-32 m3
(a) 1 dyne = 10-5 N
Force
(b) 1 kgf = 9
...
81Nm-2
(b) 1 mm of Hg = 133 Nm-2
Pressure
(c) 1 pascal = 1 Nm-2
(d) 1 atmosphere pressure = 76 cm of Hg = 1
...
81 J
Work and energy
(c) 1 kWh = 3
...
6 x 10-19 J
(d) 1 kgf- ms-1 = 9
...


5
...


7
...

2
...

4
...


1 fermi =10-15 m
1 X-ray unit = 10-13 m
1 astronomical unit = 1
...
46 x 1015 m
1 parsec = 3
...
26 light year

Some Approximate Masses
Object
Kilogram
Our galaxy 2 x 1041
Sun
2 x 1030
Moon
7 x 1022
Asteroid Eros 5 x 1015

Dimensions
Dimensions of any physical quantity are those powers which are raised on fundamental units to
express its unit
...

Dimensional Formula of Some Physical Quantities
Physical

Dimensional

MKS

S
...

Quantity

Formula

Unit

www
...
com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)

4|Page

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

Area
[L2]
metre2
Volume
[L3]
metre3
Velocity
[LT-1]
ms-1
Acceleration
[LT-2]
ms-2
Force
[MLT-2]
newton (N)
2 -2
Work or energy
[ML T ]
joule (J)
2 -3
Power
[ML T ]
J s-1 or watt
Pressure or stress
[ML-1T-2]
Nm-2
Linear momentum or Impulse [MLT-1]
kg ms-1
Density
[ML-3]
kg m-3
Strain
Dimensionless Unitless
Modulus of elasticity
[ML-1T-2]
Nm-2
Surface tension
[MT-2]
Nm-1
Velocity gradient
T-1
second-1
Coefficient of velocity
[ML-1T-1]
kg m-1s-1
Gravitational constant
[M-1L3T-2]
Nm2/kg2
Moment of inertia
[ML2]
kg m2
Angular velocity
[T-1]
rad/s
-2
Angular acceleration
[T ]
rad/S2
Angular momentum
[ML2T-1]
kg m2S-1
Specific heat
L2T-2θ-1
kcal kg-1K-1
Latent heat
[L2T-2]
kcal/kg
2 -1
Planck’s constant
ML T
J-s
Universal gas constant
[ML2T-2θ-1] J/mol-K

Homogeneity Principle
If the dimensions of left hand side of an equation are equal to the dimensions of right hand side
of the equation, then the equation is dimensionally correct
...

Mathematically [LHS] = [RHS]
Applications of Dimensions
1
...

2
...

3
...

Significant Figures
In the measured value of a physical quantity, the number of digits about the correctness of
which we are sure plus the next doubtful digit, are called the significant figures
...
ncerthelp
...
All non-zeros digits are significant figures, e
...
, 4362 m has 4 significant figures
...
All zeros occuring between non-zero digits are significant figures, e
...
, 1005 has 4
significant figures
...
All zeros to the right of the last non-zero digit are not significant, e
...
, 6250 has only 3
significant figures
...
In a digit less than one, all zeros to the right of the decimal point and to the left of a nonzero digit are not significant, e
...
, 0
...

5
...
g
...
4750
has 5 significant figures
...
e
...
,
If l1= 4
...
50 m
Then, l1 + l2 = (4
...
50) m = 5
...
83 m
(ii) In Multiplication or Division In multiplication or division of the numerical values, the final
result should retain the least significant figures as the various numerical values
...
g
...
5 m and breadth b = 4
...

Then, area A = l x b = 12
...
125 = 51
...
6 m2
Rules of Rounding Off Significant Figures
1
...
e
...
,
1
...
5
...
If the digit to be dropped is greater than 5, then the preceding digit is raised by one
...
g
...
49 is rounded off to 2
...

3
...
e
...
, 3
...
6
...
If the digit to be dropped is 5 or 5 followed by zeros, then the preceding digit is raised by
one, if it is odd and left unchanged if it is even
...
g
...
750 is rounded off to 3
...
650 is rounded off to 4
...

www
...
com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)

6|Page

Error
The lack in accuracy in the measurement due to the limit of accuracy of the instrument or due
to any other cause is called an error
...
Absolute Error
The difference between the true value and the measured value of a quantity is called absolute
error
...


The absolute error in measured values is given by
Δa1 = am – a1
Δa2 = am – a1
…………
...
Mean Absolute Error
The arithmetic mean of the magnitude of absolute errors in all the measurement is called mean
absolute error
...
Relative Error The ratio of mean absolute error to the true value is called relative

4
...


www
...
com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)

7|Page

Propagation of Error
(i) Error in Addition or Subtraction Let x = a + b or x = a – b
If the measured values of two quantities a and b are (a ± Δa and (b ± Δb), then maximum
absolute error in their addition or subtraction
...

If the measured values of a and b are (a ± Δa) and (b ± Δb), then maximum relative error

www
...
com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)



---